gated.proto(4) Kernel Interfaces Manual gated.proto(4)
NAME
gated.proto - Gate daemon configuration file (protocol statements)
DESCRIPTION
Routing protocols determine the "best" route to each destination and distribute routing information among the systems on a network. Rout-
ing protocols are divided into two general groups: interior (intra-domain) and exterior (inter-domain) protocols. The gated software com-
bines management of the interior and exterior routing protocols in one software daemon.
Intra-Domain Routing Protocols
Intra-domain (interior) protocols are used to exchange reachability information within an autonomous system (AS). They are referred to as
a class by the acronym IGP. The following interior protocols are supported: The Routing Information Protocol, Version 1 and Version 2, is
the most commonly used interior protocol. RIP selects the route with the lowest metric as the best route. The metric is a hop count rep-
resenting the number of gateways through which data must pass to reach its destination. The longest path that RIP accepts is 15 hops. If
the metric is greater than 15, a destination is considered unreachable and gated discards the route. RIP assumes the best route is the one
that uses the fewest gateways (the shortest path), not taking into account congestion or delay on route.
The RIP version 1 protocol is described in RFC 1058; the RIP version 2 protocol is described in RFC 11723. Open Shortest Path First
(OSPF) is a link-state protocol. OSPF is better suited than RIP for complex networks with many routers. OSPF provides equal cost
multipath routing.
OSPF is described in RFC 2178; OSPF Version 2 is described in RFC 1583. The OSPF Version 2 MIB is defined in RFC 1850. Other
related documents are RFC 1245, RFC 1246, and RFC 1370.
Exterior Routing Protocols
Exterior protocols are used to exchange routing information between autonomous systems. Exterior protocols are only required when an au-
tonomous system must exchange routing information with another autonomous system. Routers within an autonomous system run an interior
routing protocol like RIP. Only those gateways that connect an autonomous system to another autonomous system need to run an exterior
routing protocol. The following exterior protocols are supported by gated: Exterior Gateway Protocol (EGP). Originally EGP reachability
information was passed into ARPANET/MILNET "core" gateways where the best routes were chosen and passed back out to all connected autono-
mous systems. As the Internet moved toward a less hierarchical architecture, EGP, an exterior routing protocol that assumes a hierarchical
structure, became less effective.
The EGP protocol is described in RFC 827 and RFC 904. Border Gateway Protocol (BGP) is replacing EGP as the exterior protocol of
choice. BGP exchanges reachability information between autonomous systems, but provides more capabilities than EGP. BGP uses path
attributes to provide more information about each route as an aid in selecting the best route. Path attributes can include, for
example, administrative preferences based on political, organizational, or security (policy) considerations in the routing decision.
BGP supports nonhierarchical topologies and can be used to implement a network structure of equivalent autonomous systems.
BGP version 1 is described in RFC 1105, version 2 in RFC 1163, version 3 in RFC 1267, and version 4 in RFC 1771. The version 3 MIB
is described in RFC 1269. The documents RFC 1164, RFC 1268, and RFC 1772 describe the application of version 2, 3, and 4 in the
Internet. A protocol analysis of and experience with BGP version 3 are available in RFC 1265 and RFC 1266. RFC 1397 talks about
advertising a default route in BGP version 2 and 3.
The BGP-4 MIB is draft standard, but schedule to go to standard. Other references for BGP are: RFC 1997 for BGP Communities, RFC
1966 for BGP Route Reflection, RFC 1966 for BGP AS Confederations, and RFC 1403 for BGP - OSPF interaction. A useful application
document is RFC 1998, "An Application of the BGP Community Attribute in Multi-home Routing".
Other Routing Protocols
The following routing protocol is also supported: The Router Discovery protocol is used to inform hosts of the availability of hosts it can
send packets to and is used to supplement a statically configured default router. This is the preferred protocol for hosts to run, they are
discouraged from wiretapping routing protocols.
Router Discovery is described in RFC 1256.
Routing Information Protocol (RIP)
One of the most widely used interior gateway protocols is the Routing Information Protocol (RIP). RIP is an implementation of a distance-
vector, or Bellman-Ford routing protocol for local networks. It classifies routers as active and passive (silent). Active routers adver-
tise their routes (reachability information) to others; passive routers listen and update their routes based on advertisements, but do not
advertise. Typically, routers run RIP in active mode, while hosts use passive mode.
A router running RIP in active mode broadcasts updates at set intervals. Each update contains paired values where each pair consists of an
IP network address and an integer distance to that network. RIP uses a hop count metric to measure the distance to a destination. In the
RIP metric, a router advertises directly connected networks at a metric of 1. Networks that are reachable through one other gateway are
two hops, and so on. Thus, the number of hops or hop count along a path from a given source to a given destination refers to the number of
gateways that a datagram encounters along that path. Using hop counts to calculate shortest paths does not always produce optimal results.
For example, a path with hop count 3 that crosses three Ethernets might be substantially faster that a path with a hop count 2 that crosses
two slow-speed serial lines. To compensate for differences in technology many routers advertise artificially high hop counts for slow
links.
As delivered with most UNIX systems, RIP is run by the routing daemon, routed (pronounced route-"d"). A RIP routing daemon dynamically
builds on information received through RIP updates. When started, it issues a REQUEST for routing information and then listens for
responses to the request. If a system configured to supply RIP hears the request, it responds with a RESPONSE packet based on information
in its routing database. The RESPONSE packet contains destination network addresses and the routing metric for each destination.
When a RIP RESPONSE packet is received, the routing daemon takes the information and rebuilds the routing database adding new routes and
better (lower metric) routes to destinations already listed in the database. RIP also deletes routes from the database if the next router
to that destination says the route contains more than 15 hops, or if the route is deleted. All routes through a gateway are deleted if no
updates are received from that gateway for a specified time period. In general, routing updates are issued every 30 seconds. In many
implementations, if a gateway is not heard from for 180 seconds, all routes from that gateway are deleted from the routing database. This
180 second interval also applies to deletion of specific routes.
RIP version 2 (more commonly known as RIP II) adds capabilities to RIP. Some of these capabilities are compatible with RIP I and some are
not. To avoid supplying information to RIP I routes that could be misinterpreted, RIP II can only use non-compatible features when its
packets are multicast. On interfaces that are not capable of IP multicast, RIP I-compatible packets are used that do not contain poten-
tially confusing information.
The following is a list of main RIP II enhancements: The primary ones are the ability to advertise a next hop to use other than the router
supplying the routing update. This is quite useful when advertising a static route to a dumb router that does not run RIP as it avoids
having packets destined through the dumb router from having to cross a network twice.
RIP I routers ignore next hop information in RIP II packets. This might result in packets crossing a network twice, which is
exactly what happens with RIP I. So this information is provided in RIP I-compatible RIP II packets. RIP I assumes that all sub-
networks of a given network have the same network mask. It uses this assumption to calculate the network masks for all routes
received. This assumption prevents subnets with different netmasks from being included in RIP packets. RIP II adds the ability to
explicitly specify the network mask with each network in a packet.
While RIP I routers will ignore the network mask in RIP II packets, their calculation of the network mask will quite possibly be
wrong. For this reason, RIP I-compatible RIP II packets must not contain networks that would be misinterpreted. These network must
only be provided in native RIP II packets that are multicast.
RIP-I derives the network mask of received networks and hosts from the network mask of the interface the packet via which the packet
was received. If a received network or host is on the same natural network as the interface over which it was received and that
network is subnetted (the specified mask is more specific than the natural netmask), the subnet mask is applied to the destination.
If bits outside the mask are set it is assumed to be a host, otherwise it is assumed to be a subnet.
On point-to-point interfaces, the netmask is applied to the remote address. The netmask on these interfaces is ignored if it
matches the natural network of the remote address or is all ones.
Unlike in previous releases, the zero subnet mask (a network that matches the natural network of the interface, but has a more spe-
cific, or longer, network mask) is ignored. If this is not desirable, a route filter can be used to reject it. RIP II packets can
also contain one of two types of authentication string that can be used to verify the validity of the supplied routing data.
Authentication can be used in RIP I-compatible RIP II packets, but be aware that RIP I routers ignore it.
The first method is a simple password in which an authentication key of up to 16 characters is included in the packet. If this does
not match what is expected, the packet will be discarded. This method provides very little security as it is possible to learn the
authentication key by watching RIP packets.
The second method uses the MD5 algorithm to create a crypto-checksum of a RIP packet and an authentication key of up to 16 charac-
ters. The transmitted packet does not contain the authentication key itself, instead it contains a crypto-checksum, called the
digest. The receiving router will perform a calculation using the correct authentication key and discard the packet if the digest
does not match. In addition, a sequence number is maintained to prevent the replay of older packets. This method provides a much
stronger assurance that routing data originated from a router with a valid authentication key.
Two authentication methods can be specified per interface. Packets are always sent using the primary method, but received packets
are checked with both the primary and secondary methods before being discarded. In addition, a separate authentication key is used
for non-router queries.
RIP Syntax
rip yes | no | on | off [ {
broadcast ;
nobroadcast ;
nocheckzero ;
preference preference ;
defaultmetric metric ;
query authentication [none | [[simple|md5] password]] ;
interface interface_list
[noripin] | [ripin]
[noripout] | [ripout]
[metricin metric]
[metricout metric]
[version 1]|[version 2 [multicast|broadcast]]
[[secondary] authentication [none | [[simple|md5] password]] ;
trustedgateways gateway_list ;
sourcegateways gateway_list ;
traceoptions trace_options ; } ] ;
The rip statement enables or disables RIP. If the rip statement is not specified the default is rip on;. If enabled, RIP assumes nobroad-
cast when there is only one interface and broadcast when there is more than one. The following rip options are supported: Specifies that
RIP packets are broadcast regardless of the number of interfaces present. This is useful when propagating static routes or routes learned
from anther protocol into RIP. In some cases, the use of broadcast when only one network interface is present can cause data packets to
traverse a single network twice. Specifies that RIP packets are not broadcast on attached interfaces, even if there are more than one. If
a sourcegateways clause is present, routes are unicast directly to that gateway. Specifies that RIP should not make sure that reserved
fields in incoming version 1 RIP packets are zero. Normally RIP rejects packets when the reserved fields are zero. Sets the preference
for routes learned from RIP. The default preference is 100. This preference can be overridden by a preference specified in import policy.
Defines the metric used when advertising routes via RIP that were learned from other protocols. If not specified, the default value is 16
(unreachable). This choice of values requires you to explicitly specify a metric in order to export routes from other protocols into RIP.
This metric can be overridden by a metric specified in export policy. Specifies the authentication required of query packets that do not
originate from routers. The default is none. Controls various attributes of sending RIP on specific interfaces. See the Interface Lists
section in gated.conf(4) for the description of the interface_list.
Note that if there are multiple interfaces configured on the same subnet, RIP updates are sent from first one on which RIP output is
configured.
The following interface parameters are supported: Specifies that RIP packets received via the specified interface are ignored. The
default is to listen to RIP packets on all non-loopback interfaces. This is the default. This argument might be necessary when
noripin is used on a wild card interface descriptor. Specifies that no RIP packets are sent on the specified interfaces. The
default is to send RIP on all broadcast and non-broadcast interfaces when in broadcast mode. The sending of RIP on point-to-point
interfaces must be manually configured. This is the default. This argument is necessary when it is desired to send RIP on point-
to-point interfaces and might be necessary when noripin is used on a wild card interface descriptor. Specifies the RIP metric to
add to incoming routes before they are installed in the routing table. The default is the kernel interface metric plus 1 (which is
the default RIP hop count). If this value is specified, it is used as the absolute value, the kernel metric is not added. This
option is used to make this router prefer RIP routes learned via the specified interface(s) less than RIP routes from other inter-
faces. Specifies the RIP metric to be added to routes that are send via the specified interface(s). The default is zero. This
option is used to make other routers prefer other sources of RIP routes over this router. Specifies that RIP packets sent via the
specified interface(s) are version 1 packets. This is the default. Specifies that RIP version 2 packets are sent on the specified
interfaces(s). If IP multicast support is available on this interface, the default is to send full version 2 packets. If it is not
available, version 1 compatible version 2 packets are sent. Specifies that RIP version 2 packets should be multicast on this inter-
face. This is the default. Specifies that RIP version 1-compatible version 2 packets should be broadcast on this interface, even
if IP multicast is available. Defines the authentication type to use. It applies only to RIP version 2 and is ignored for RIP-1
packets. The default authentication type is none. If a password is specified, the authentication type defaults to simple. The
password should be a quoted string with between 0 and 16 characters.
If secondary is specified, this defines the secondary authentication. If omitted, the primary authentication is specified. The
default is primary authentication of none and no secondary authentication. Defines the list of gateways from which RIP will accept
updates. The gateway_list is a list of host names or IP addresses. By default, all routers on the shared network are trusted to
supply routing information. But if the trustedgateways clause is specified, only updates from the gateways in the list are
accepted. Defines a list of routers to which RIP sends packets directly, not through multicast or broadcast. This can be used to
send different routing information to specific gateways. Updates to gateways in this list are not affected by noripout on the
interface. Specifies the tracing options for RIP. (See the Trace Options Statement section in gated.conf(4) and the RIP-specific
tracing options that follow.)
RIP Tracing options
The policy option logs info whenever a new route is announced, the metric being announced changes, or a route goes or leaves holddown. The
following packet tracing options, which can be modified with detail, send, or recv, are supported: All RIP packets. RIP information
request packets, such as REQUEST, POLL and POLLENTRY RIP RESPONSE packets, which is the type of packet that actually contains routing
information. Any other type of packet. The only valid ones are TRACE_ON and TRACE_OFF both of which are ignored.
The OSPF Protocol
Open Shortest Path Routing (OSPF) is a shortest path first (SPF) or link-state protocol. OSPF is an interior gateway protocol that dis-
tributes routing information between routers in a single autonomous system. OSPF chooses the least cost path as the best path. Suitable
for complex networks with a large number of routers, OSPF provides equal cost multipath routing where packets to a single destination can
be sent via more than one interface simultaneously.
In a link-state protocol, each router maintains a database describing the entire AS topology, which it builds out of the collected link
state advertisements of all routers. Each participating router distributes its local state (the router's usable interfaces and reachable
neighbors) throughout the AS by flooding. Each multiaccess network that has at least two attached routers has a designated router and a
backup designated router. The designated router floods a link state advertisement for the multiaccess network and has other special
responsibilities. The designated router concept reduces the number of adjacencies required on a multiaccess network.
OSPF allows networks to be grouped into areas. Routing information passed between areas is abstracted, potentially allowing a significant
reduction in routing traffic. OSPF uses four different types of routes, listed in order of preference: intra-area, inter-area, type 1
external and type 2 external. Intra-area paths have destinations within the same area, inter-area paths have destinations in other OSPF
areas and Autonomous System External (ASE) routes are routes to destinations external to the AS. Routes imported into OSPF as type 1
routes are supposed to be from igps whose external metrics are directly comparable to OSPF metrics. When a routing decision is being made,
OSPF adds the internal cost to the AS Border router to the external metric. Type 2 ASEs are used for egps whose metrics are not comparable
to OSPF metrics. In this case, only the internal OSPF cost to the AS Border router is used in the routing decision.
From the topology database, each router constructs a tree of the shortest paths with itself as the root. This shortest-path tree gives the
route to each destination in the AS. Externally derived routing information appears on the tree as leaves. The link-state advertisement
format distinguishes between information acquired from external sources and information acquired from internal routers, so there is no
ambiguity about the source or reliability of routes. Externally derived routing information (for example, routes learned from EGP or BGP)
is passed transparently through the autonomous system and is kept separate from OSPF's internally derived data. Each external route can
also be tagged by the advertising router, enabling a passing of additional information between routers on the borders of the autonomous
system.
OSPF optionally includes type of service (TOS) routing and allows administrators to install multiple routes to a given destination for each
type of service (for example, low delay or high throughput). A router running OSPF uses the destination address and the type of service to
choose the best route to the destination.
OSPF intra- and inter-area routes are always imported into the gated routing database with a preference of 10. It would be a violation of
the protocol if an OSPF router did not participate fully in the area's OSPF, so it is not possible to override this. Although it is possi-
ble to give other routes lower preference values explicitly, it is ill-advised to do so.
Hardware multicast capabilities are also used where possible to deliver link-status messages. OSPF areas are connected by the backbone
area, the area with identifier 0.0.0.0. All areas must be logically contiguous and the backbone is no exception. To permit maximum flexi-
bility, OSPF allows the configuration of virtual links enable the backbone area to appear contiguous despite the physical reality.
All routers in an area must agree on that area's parameters. A separate copy of the link-state algorithm is run for each area. Because of
this, most configuration parameters are defined on a per area basis. All routers belonging to an area must agree on that area's configura-
tion. Misconfiguration will lead to adjacencies not forming between neighbors, and routing information might not flow, or even loop.
Authentication
All OSPF protocol exchanges can be authenticated. Authentication guarantees that routing information is only imported from trusted
routers, to protect the Internet and its users. A variety of authentication schemes can be used but a single scheme must be configured for
each interface. This enables some interfaces to use much stricter authentication than others. The following authentication schemes are
available: No authentication. To use no authentication, add the following line to the appropriate OSPF interface statements: auth none ;
Simple authentication key. Use this to prevent certain routers from exchanging OSPF packets. The interfaces that the packets are to be
sent on still need to be trusted because the key will be placed in the packets and can be seen by anyone with access to the network.
To specify simple authentication, add the following line to your OSPF interface statements: auth simple auth_key; In the preceding
line, auth_key is a string of up to 8 characters, and is standardized. MD5 authentication. Use this when you do not trust other
users of your network. This system works by using shared secret keys. Because the keys are used to sign the packets with an MD5
checksum, they cannot be forged or tampered with. Because the keys are not included in the packet, snooping the key is not possi-
ble. Users of the network can still snoop the contents of packets, however, because the packets are not encrypted.
MD5 authentication is compliant with the OSPF specification in RFC 2178. This specification uses the MD5 algorithm and an authenti-
cation key of up to 16 characters. RFC 2178 allows multiple MD5 keys per interface. Each key has two associated time ranges.
To specify a single MD5 key on an interface, add the following to the appropriate OSPF interface statements: auth md5 md5-key where
md5-key is: key your-key id id-number [ {
[ start-generate date-time ; ]
[ stop-generate date-time ; ]
[ start-accept date-time ; ]
[ stop-accept date-time ; ] } ] ; Where id-number is an integer with a value between 1 and 255 and date-time is in the format
YYYY/MM/DD HH:MM (If any time fields are used, all are required).
If no value is given for the time ranges, the default values are: key is always generated key is always accepted
Thus, if you always want your key to be accepted, simply specify a sequence such as: auth md5 key "mikeyone" id 1; To specify multi-
ple MD5 keys on an interface, add the following to the appropriate OSPF interface statements: auth md5 {
md5-key
md5-key
.
.
.
md5-key } ; For example, two routers may start out generating key 1 and want to switch to key 2 at 6:00 GMT. In order to make
the transition between keys easier, the routers agree to stop generating key 1 at 6:00 GMT, but accept key 1 until 6:10 GMT. Key 2
is accepted 10 minutes before the planned switch time (5:50 GMT). These overlapping ranges allow the clocks on the routers to be
slightly out of syncronization. You can specify this sequence of keys as follows: auth md5 {
key "mikeyone" id 1 {
stop-generate 1999/05/01 06:00;
stop-accept 1999/05/01 06:10;
};
key "mikeytwo" id 2 {
start-generate 1999/05/01 06:00;
start-accept 1999/05/01 05:50;
}; };
OSPF Syntax
ospf yes | no | on | off [ {
defaults {
preference preference ;
cost cost ;
tag [as] tag ;
type 1 | 2 ;
inherit-metric ;
} ;
exportlimit routes ;
exportinterval time ;
traceoptions trace_options ;
syslog [first pktcnt][ every every_pktcnt] ;
monitorauthkey authkey ;
area area | backbone {
stub [cost cost] ;
networks {
network [restrict] ;
network mask mask [restrict] ;
network masklen number [restrict] ;
host host [restrict] ;
} ;
stubhosts {
host cost cost ;
} ;
interface interface_list; [cost cost] [ {
enable | disable ;
interface_parameters
} ] ;
interface interface_list nonbroadcast [cost cost] [ {
pollinterval time ;
routers {
gateway [eligible] ;
} ;
interface_parameters
} ] ;
Backbone only:
virtuallink neighborid router_id transitarea area {
interface_parameters
} ;
} ; } ] ; Specify the defaults used when importing OSPF Autonomous System External (ASE) routes into the gated routing table and
exporting routes from the gated routing table into OSPF ASEs. The preference is used to determine how OSPF routes compete with routes from
other protocols in the gated routing table. The default value is 150. The cost is used when exporting a non-OSPF route from the gated
routing table into OSPF as an ASE. The default value is 1. This can be explicitly overridden in export policy. OSPF ASE routes have a
32-bit tag field that is not used by the OSPF protocol, but might be used by export policy to filter routes. When OSPF is interacting with
an EGP, the tag field can be used to propagate AS path information, in which case the as keyword is specified and the tag is limited to 12
bits of information. If not specified, the tag is set to zero. Routes exported from the gated routing table into OSPF default to becoming
type 1 ASEs. This default can be explicitly changed here and overridden in export policy. Enables an OSPF ASE route to inherit the metric
of the external route when no metric is specified on the export. This option maintains compatibility with all the current export functions:
A metric specified on the export will take precedence. The cost specified in the default will be used if inherit-metric is not specified.
Because of the nature of OSPF, the rate at which ASEs are flooded must be limited. The following two parameters can be used to adjust
those rate limits: Specifies how often a batch of ASE link state advertisements are generated and flooded into OSPF. The default is once
per second. Specifies how many ASEs are generated and flooded in each batch. The default is 100. Specifies the tracing options for OSPF.
(See gated.conf(4) and the OSPF tracing options section.) Specifies the tracing options for logging OSPF packets. The log will contain the
first pkcnt packets for every type of OSPF packet. After the first pckcnt packets, the syslog will only save one message per every
every_pktcnt packets. OSPF state can be queried using the ospf_monitor (This should be a hyperlink) utility. This utility sends non-stan-
dard OSPF packets that generate a text response from OSPF. By default, these requests are not authenticated; if an authentication key is
configured, the incoming requests must match the specified authentication key. No OSPF state can be changed by these packets, but the act
of querying OSPF can utilize system resources. Each OSPF router must be configured into at least one OSPF area. If more than one area is
configured, at least one must the be backbone. The backbone can only be configured using the backbone keyword, it cannot be specified as
area 0. The backbone interface can be a virtuallink. A stub area is one in which there are no ASE routes. If a cost is specified, this
injects a default route into the area with the specified cost. The networks list describes the scope of an area. Intra-area LSAs that
fall within the specified ranges are not advertised into other areas as inter-area routes. Instead, the specified ranges are advertised as
summary network LSAs. If restrict is specified, the summary network LSAs are not advertised. Intra-area LSAs that do not fall into any
range are also advertised as summary network LSAs. This option is very useful on well designed networks in reducing the amount of routing
information propagated between areas. The entries in this list are either networks or a subnetwork/mask pair. See the section on "Route
Filtering" in gated.control(4) for more detail about specifying ranges. Specifies directly attached hosts that should be advertised as
reachable from this router and the costs they should be advertised with. Point-to-point interfaces on which it is not desirable to run
OSPF should be specified here.
It is also useful to assign an additional address to the loopback interface (one not on the 127 network) and advertise it as a stub
host. If this address is the same one used as the router-id, it enables routing to OSPF routers by router-id instead of by inter-
face address. This is more reliable than routing to one of the router's interface addresses, which might not always be reachable.
This form of the interface clause is used to configure a broadcast (which requires IP multicast support) or a point-to-point inter-
face. See the "Interfaces Statement" section in gated.conf(4) for the description of the interface_list parameters.
Each interface has a cost. The costs of all interfaces a packet must cross to reach a destination are summed to get the cost to
that destination. The default cost is one, but another non-zero value can be specified.
This form has one unique parameter: Enables or disables the interface. See the "Interface Parameters" section for a list of parame-
ters common to all interface types. This form of the interface clause is used to specify a nonbroadcast interface on a non-broad-
cast multi-access (NBMA) medium. Because an OSPF broadcast medium must support IP multicasting, a broadcast-capable medium that
does not support IP multicasting must be configured as a non-broadcast interface.
A non-broadcast interface supports any of the standard interface clauses listed previously and the following two that are specific
to non-broadcast interfaces: Before adjacency is established with a neighbor, OSPF packets are sent periodically at the specified
poll interval. By definition, it is not possible to send broadcast packets to discover OSPF neighbors on a non-broadcast, so all
neighbors must be configured. The list includes one or more neighbors and an indication of their eligibility to become a designated
router. See the "Interface Parameters" section for a list of parameters common to all interface types. Virtual links are used to
establish or increase connectivity of the backbone area. The neighborid is the router_id of the other end of the virtual link. The
transit area specified must also configured on this system. All standard interface parameters defined by the interface clause can
be specified on a virtual link.
See the "Interface Parameters" section for a list of parameters common to all interface types.
Interface Parameters
The following interface parameters are common to all types of interfaces: The number of seconds between link state advertisement retrans-
missions for adjacencies belonging to this interface. The estimated number of seconds required to transmit a link state update over this
interface. The transitdelay parameter takes into account transmission and propagation delays and must be greater than 0. A number between
0 and 255 specifying the priority for becoming the designated router on this interface. When two routers attached to a network both
attempt to become designated router, the one with the highest priority wins. A router whose router priority is set to 0 is ineligible to
become designated router. The length of time, in seconds, between Hello packets that the router sends on the interface. The length of
time, in seconds, a router's neighbors wait to hear a router's Hello packets before the they declare the router down. Do not send or
receive packets on this interface. This has the effect of originating a stub link to this interface into the domain. Used by OSPF authen-
tication to generate and verify the authentication field in the OSPF header. The authentication key can be configured on a per interface
basis. It is specified by one to eight decimal digits separated by periods, a one- to eight-byte hexadecimal string preceded by 0x, or a
one to eight character string in double quotes. See the "Authentication" section for additional information.
Specify MD5 authentication with the md5-key, which is specified as: key auth-key id id-number [ {
[start-generate date-time;]
[stop-generate date-time;]
[start-accept date-time;]
[stop-accept date-time;] }]; Where auth-key is a one-to-eight character string, id-number is an integer with a value between 1
and 255, and date-time is in the format YYYY/MM/DD HH:MM. If any time fields are used, all are required.
See the "Authentication" section for additional information. Used by OSPF authentication to generate and verify the secondary
authentication field in the OSPF header. The authentication key can be configured on a per-interface basis. It is specified by one
to eight decimal digits separated by periods, a one-to-eight byte hexadecimal string preceded by 0x, or a one-to-eight character
string in double quotes. See the "Authentication" section for more information.
Point-to-point interfaces also support the following parameter: By default, OSPF packets to neighbors on point-to-point interfaces
are sent via the IP multicast mechanism. Some implementations of IP multicasting for UNIX, however, have a bug that precludes the
use of IP multicasting on these interfaces. The gated daemon detects this condition and falls back to using sending unicast OSPF
packets to this point-to-point neighbor.
If the use of IP multicasting is not desired because the remote neighbor does not support it, the nomulticast parameter can be spec-
ified to force the use of unicast OSPF packets. You can also use this option to eliminate warnings when gated detects the previ-
ously described bug.
OSPF Tracing options
In addition to the following OSPF specific trace flags, OSPF supports the state that traces interface and neighbor state machine transi-
tions. Creates the Link State Advertisement Traces the link state packets transmitted Traces the link state packets received Traces the
Shortest Path First (SPF) calculations Traces OSPF at the debugging level of detail The following packet tracing options, which can be mod-
ified with detail, send, and recv, are supported: OSPF HELLO packets, which are used to determine neighbor reachability. OSPF Database
Description packets, which are used in synchronizing OSPF databases. OSPF Link State Request packets, which are used in synchronizing OSPF
databases. OSPF Link State Update packets, which are used in synchronizing OSPF databases. OSPF Link State Ack packets, which are used in
synchronizing OSPF databases.
The Exterior Gateway Protocol (EGP)
The Exterior Gateway Protocol (EGP) is an exterior routing protocol used for exchanging routing information with gateways in other autono-
mous systems. Unlike interior protocols, EGP propagates only reachability indications, not true metrics. EGP updates contain metrics,
called distances, that range from 0 to 255. The gated daemon compares EGP distances learned from the same AS.
Before EGP sends routing information to a remote router, it must establish an adjacency with that router. This is accomplished by an
exchange of Hello (not to be confused with the HELLO protocol or OSPF HELLO messages) and I Heard You (I-H-U) messages with that router.
Computers communicating via EGP are called EGP neighbors, and the exchange of HELLO and I-H-U messages is referred to as acquiring a neigh-
bor.
Once the neighbor is acquired, the system polls the neighbor for routing information. The neighbor responds by sending an update contain-
ing routing information. If the system receives a poll from its neighbor, it responds with its own update packet. When the system
receives an update, it includes routes from the update into its routing database. If the neighbor fails to respond to three consecutive
polls, gated assumes that the neighbor is down and removes the neighbor's routes from its database.
EGP Syntax
egp yes | no | on | off [ {
preference preference ;
defaultmetric metric ;
packetsize number ;
traceoptions trace_options ;
group
[peeras autonomous_system]
[localas autonomous_system]
[maxup number]
{
neighbor host
[preference preference]
[preference2 preference]
[metricout metric]
[nogendefault]
[importdefault]
[exportdefault]
[gateway gateway]
[lcladdr local_address]
[sourcenet network]
[minhello | p1 time]
[minpoll | p2 time]
[ttl ttl]
[traceoptions trace_options]
;
} ; } ] ;
Sets the preference for routes learned from RIP. The default preference is 200. This preference can be overridden by a preference speci-
fied on the group or neighbor statements or by import policy. Defines the metric used when advertising routes via EGP. If not specified,
the default value is 255, which some systems can consider unreachable. This choice of values requires you to explicitly specify a metric
when exporting routes to EGP neighbors. This metric can be overridden by a metric specified on the neighbor or group statements or in
export policy. Defines the expected maximum size of a packet that EGP expects to receive from this neighbor. If a packet larger than this
value is received, it is incomplete and is discarded. The length of this packet is noted and the expected size is increased to be able to
receive a packet of this size. Specifying the parameter here prevents the first packet from being dropped. If not specified, the default
size is 8192 bytes. All packet sizes are rounded up to a multiple of the system page size. Specifies the tracing options for EGP. By
default these are inherited from the global trace options. These values can be overridden on a group or neighbor basis. (See the Trace
Options Statement section in gated.conf(4) and the EGP-specific tracing options that follow.) EGP neighbors must be specified as members
of a group. A group is usually used to group all neighbors in one autonomous system. Parameters specified on the group clause apply to
all of the subsidiary neighbors unless explicitly overridden on a neighbor clause. Any number of group clauses can specify any number of
neighbor clauses.
Any parameters from the neighbor subclause can be specified on the group clause to provide defaults for the whole group (which can
be overridden for individual neighbors). In addition, the group clause is the only place to set the following attributes: Identi-
fies the autonomous system number expected from peers in the group. If not specified, it is learned dynamically. Identifies the
autonomous system that gated is representing to the group. The default is that which has been set globally in the autonomoussystem
statement. This option is usually only used when masquerading as another autonomous system and its use is discouraged. Specifies
the number of neighbors gated should acquire from this group. The default is to acquire all of the neighbors in the group. The
gated daemon attempts to acquire the first maxup neighbors in the order listed. If one of the first neighbors is not available, it
acquires one farther down the list. If after start-up gated does manage to acquire the more desirable neighbor, it drops the less
desirable one. Each neighbor subclause defines one EGP neighbor within a group. The only part of the subclause that is required is
the neighbor_address argument, which is the symbolic host name or IP address of the neighbor. The following parameters are
optional: Specifies the preference used for routes learned from these neighbors. This can differ from the default EGP preference
set in the egp statement, so that gated can prefer routes from one neighbor, or group of neighbors, over another. This preference
can be explicitly overriden by import policy. In the case of a preference tie, the second preference, preference2, can be used to
break the tie. The default value is 0. Defines a metric to be used for all routes sent to this neighbor. The value overrides the
default metric set in the egp statement and any metrics specified by export policy, but only for this specific neighbor or group of
neighbors. Prevents gated from generating a default route when EGP receives a valid update from its neighbor. The default route is
generated only when the gendefault option is enabled. Enables gated to accept the default route (0.0.0.0) if it is included in a
received EGP update. If not specified, the default route contained in an EGP update is ignored. For efficiency, some networks have
external routers announce a default route to avoid sending large EGP update packets. Enables gated to include the default route
(0.0.0.0) in EGP updates sent to this EGP neighbor. This allows the system to advertise the default route via EGP. Normally a
default route is not included in EGP updates. If a network is not shared with a neighbor, gateway specifies a router on an attached
network to be used as the next hop router for routes received from this neighbor. This option is rarely used. Specifies the
address used on the local end of the connection with the neighbor. The local address must be on an interface that is shared with
the neighbor or with the neighbor's gateway when the gateway parameter is used. A session is opened only when an interface with the
appropriate local address (through which the neighbor or gateway address is directly reachable) is operating. Specifies the network
queried in the EGP Poll packets. By default this is the network shared with neighbors address specified. If there is no network
shared with the neighbor, specify one of the networks to which the neighbor is attached. You can also use this parameter to specify
a network shared with the neighbor other than the one on which the EGP packets are sent. This parameter is normally not needed.
Sets the minimum acceptable interval between the transmission of EGP HELLO packets. The default hello interval is 30 seconds. If
the neighbor fails to respond to three hello packets, gated stops trying to acquire the neighbor. Setting a larger interval gives
the neighbor a better chance to respond. The minhello parameter is an alias for the P1 value defined in the EGP specification.
Sets the time interval between polls to the neighbor. The default is 120 seconds. If three polls are sent without a response, the
neighbor is declared down and all routes learned from that neighbor are removed from the routing database. A longer polling inter-
val supports a more stable routing database, but is not as responsive to routing changes. The minpoll parameter is an alias for the
P2 value defined in the EGP specification. By default, gated sets the IP TTL for local neighbors to one and the TTL for non-local
neighbors to 255. This option is provided when attempting to communicate with improperly functioning routers that ignore packets
sent with a TTL of one. Specifies the tracing options for this EGP neighbor. By default these are inherited from group or EGP
global trace options. (See the Trace Options Statement section in gated.conf(4) and the EGP tracing options that follow.)
EGP Tracing options
The state and policy options work with EGP. The following packet tracing options, which can be modified with detail, send, and recv, are
supported for the EGP protocol: Traces all EGP packets Traces EGP HELLO/I-HEARD-U packets, which are used to determine neighbor reachabil-
ity. Traces EGP ACQUIRE/CEASE packets, which are used to initiate and terminate EGP sessions. Traces EGP POLL/UPDATE packets, which are
used to request and receive reachability updates.
The BGP Protocol Statement
The Border Gateway Protocol (BGP) is an exterior routing protocol used for exchanging routing information between autonomous systems. BGP
is used for exchange of routing information between multiple transit autonomous systems as well as between transit and stub autonomous sys-
tems. BGP is related to EGP, but operates with more capability, greater flexibility, and less required bandwidth.
BGP uses path attributes to provide more information about each route, and in particular maintain an AS path, which includes the AS number
of each autonomous system the route has transited, providing information sufficient to prevent routing loops in an arbitrary topology.
Path attributes can also be used to distinguish between groups of routes to determine administrative preferences, allowing greater flexi-
bility in determining route preference to achieve a variety of administrative ends.
BGP supports two basic types of sessions between neighbours, internal (sometimes referred to as IBGP) and external. Internal sessions are
run between routers in the same autonomous system, while external sessions run between routers in different autonomous systems. When send-
ing routes to an external peer the local AS number is prepended to the AS path, hence routes received from an external peer are guaranteed
to have the AS number of that peer at the start of the path. Routes received from an internal neighbour will not in general have the local
AS number prepended to the AS path, and hence will in general have the same AS path that the route had when the originating internal neigh-
bour received the route from an external peer. Routes with no AS numbers in the path can be legitimately received from internal neigh-
bours; these indicate that the received route should be considered internal to your own AS.
The BGP implementation supports three versions of the BGP protocol, versions 2, 3 and 4. BGP versions 2 and 3 are quite similar in capa-
bility and function. They propagate only classed network routes, and the AS path is a simple array of AS numbers. BGP 4 propagates fully
general address-and-mask routes, and the AS path has some structure to represent the results of aggregating dissimilar routes.
External BGP sessions may or may not include a single metric, which BGP calls the Multi-Exit Discriminator (MED), in the path attributes.
For BGP versions 2 and 3, this metric is a 16-bit unsigned integer; for BGP version 4 it is a 32-bit unsigned integer. In either case,
smaller values of the metric are preferred. Currently this metric is only used to break ties between routes with equal preference from the
same neighbour AS.
Internal BGP sessions carry at least one metric in the path attributes, which BGP calls the LocalPref. The size of the metric is identical
to the MED. For BGP versions 2 and 3, this metric is considered better when its value is smaller; for version 4 it is better when it is
larger. BGP version 4 sessions can optionally carry a second metric on internal sessions, this being an internal version of the Multi-Exit
Discriminator. The use of these metrics is dependent on the type of internal protocol processing that is specified.
BGP collapses routes with similar path attributes into a single update for advertisement. Routes that are received in a single update are
readvertised in a single update. The churn caused by the loss of a neighbor is minimized and the initial advertisement sent during peer
establishment is maximally compressed. BGP does not read information from the kernel message-by-message, but fills the input buffer. It
processes all complete messages in the buffer before reading again. BGP also does multiple reads to clear all incoming data queued on the
socket. This feature might cause other protocols to be blocked for prolonged intervals by a busy peer connection.
All unreachable messages are collected into a single message and sent prior to reachable routes during a flash update. For these unreach-
able announcements, the next hop is set to the local address on the connection, no metric is sent and the path origin is set to incomplete.
On external connections, the AS path in unreachable announcements is set to the local AS; on internal connections, the AS path is set to
zero length.
The BGP implementation expects external peers to be directly attached to a shared subnet, and expects those peers to advertise next hops
that are host addresses on that subnet (though this constraint can be relaxed by configuration for testing). For groups of internal peers,
however, you can select one of the following group types: Type internal groups expect all peers to be directly attached to a shared subnet
so that, like external peers, the next hops received in BGP advertisements can be used directly for forwarding. Type routing groups deter-
mine the immediate next hops for routes by using the next hop received with a route from a peer as a forwarding address, and using this to
look up an immediate next hop in an IGP's routes. Such groups support distant peers, but need to be informed of the IGP whose routes they
are using to determine immediate next hops.
For internal BGP group types (and for test groups), where possible a single outgoing message is built for all group peers based on the com-
mon policy. A copy of the message is sent to every peer in the group, with possible adjustments to the next hop field as appropriate to
each peer. This minimizes the computational load of running large numbers of peers in these types of groups. BGP allows unconfigured
peers to connect if an appropriate group has been configured with an allow clause.
BGP Syntax
At the top of your configuration file, you must specify the AS and routerid in order for BGP to operate. bgp yes | no | on | off [ {
preference preference ;
defaultmetric metric ;
traceoptions trace_options ;
[clusterid host ; ]
group type (external peeras autonomous_system)
| (internal peeras autonomous_system)
| (igp peeras autonomous_system proto proto)
| (routing peeras autonomous_system proto proto
interface interface_list)
| (test peeras autonomous_system)
{
allow {
network
network mask mask
network masklen number
all
host host
} ;
peer host
[authcheck]
[gateway gateway]
[holdtime time]
[ignorefirstashop]
[keep [all | none]]
[keepalivesalways]
[lcladdr local_address]
[logupdown]
[med]
[metricout metric]
[nexthopself]
[noaggregatorid]
[nogendefault]
[nov4asloop]
[passive]
[preference preference]
[preference2 preference]
[recvbuffer number]
[sendbuffer number]
[showwarnings]
[traceoptions trace_options]
[ttl ttl]
[v3asloopokay]
[version number]
;
} ; } ] ; external | internal | igp | test
The bgp statement enables or disables BGP. By default BGP is disabled. The default metric for announcing routes via BGP is to not send a
metric.
The following options are supported: Sets the preference for routes learned from RIP. The default preference is 170. This preference can
be overridden by a preference specified on the group or peer statements or by import policy. Defines the metric used when advertising
routes via BGP. If not specified, no metric is propagated. This metric can be overridden by a metric specified on the neighbor or group
statements or in export policy. Specifies the tracing options for BGP. By default, these are inherited from the global trace options.
These values can be overridden on a group or neighbor basis. (See the Trace Options Statement section in gated.conf(4) and the BGP tracing
options that follow.) Specifies the route reflection cluster ID for BGP. The cluster ID defaults to be the same as the router ID. If a
router is to be a route reflector, you should select and configure a single cluster ID on all route reflectors in the cluster. Use the fol-
lowing guidelines in choosing a cluster ID: IDs of clusters within an AS must be unique within that AS The cluster ID must not be 0.0.0.0.
Choosing the cluster ID to be the router ID of one router in the cluster will always fulfill these criteria. If there is only one route
reflector in the cluster, the clusterid setting may be omitted because the default will suffice.
BGP Groups
BGP peers are grouped by type and the autonomous system of the peers. Any number of groups can be specified, but each must have a unique
combination of type and peer autonomous system. The following four group types are supported: In the classic external BGP group, full pol-
icy checking is applied to all incoming and outgoing advertisements. The external neighbors must be directly reachable through one of the
machine's local interfaces. By default, no metric is included in external advertisements, and the next hop is computed with respect to the
shared interface. An internal group operating where there is no IP-level IGP, for example an SMDS network or MILNET. All peers in this
group are required to be directly reachable via a single interface. All next hop information is computed with respect to this interface.
Import and export policy can be applied to group advertisements. Routes received from external BGP or EGP peers are by default readver-
tised with the received metric.
The lcladdr, outdelay, and metricout options must be set in the group clause, not on a per-peer basis, for the group types internal
and routing. If these options are set on the peer subclause, they must equal the values set on the corresponding group clause. An
internal group to which the router is not connected. The proto keyword names the interior protocol to be used to resolve BGP route
next hops, and might be the name of any IGP in the configuration, including static. An internal group that uses the routes of an
interior protocol to resolve forwarding addresses. A type routing group propagates external routes between routers that are not
directly connected, and computes immediate next hops for these routes by using the BGP next hop that arrived with the route as a
forwarding address to be resolved via an internal protocol's routing information. In essence, internal BGP is used to carry AS
external routes, while the IGP is expected to only carry AS internal routes, and the latter is used to find immediate next hops for
the former.
The proto names the interior protocol to be used to resolve BGP route next hops, and can be the name of any IGP in the configura-
tion. By default, the next hop in BGP routes advertised to type routing peers is set to the local address on the BGP connection to
those peers, as it is assumed a route to this address will be propagated via the IGP. The interface_list can optionally provide a
list interfaces whose routes are carried via the IGP for which third party next hops can be used instead.
The lcladdr, outdelay, and metricout options must be set in the group clause, not on a per-peer basis, for the group types internal
and routing. If these options are set on the peer subclause, they must equal the values set on the corresponding group clause. An
extension to external BGP that implements a fixed policy using test peers. Fixed policy and special case code make test peers rela-
tively inexpensive to maintain. Test peers do not need to be on a directly attached network. If gated and the peer are on the same
(directly attached) subnet, the advertised next hop is computed with respect to that network, otherwise the next hop is the local
machine's current next hop. All routing information advertised by and received from a test peer is discarded, and all BGP routes
that can be advertised are sent back to the test peer. Metrics from EGP- and BGP-derived routes are forwarded in the advertisement;
otherwise no metric is included.
BGP Group parameters
The BGP statement has group clauses and peer subclauses. Any number of peer subclauses can be specified within a group. A group clause
usually defines default parameters for a group of peers; these parameters apply to all subsidiary peer subclauses. Most parameters from
the peer subclause can be specified on the group clause to provide defaults for the whole group, which can be overridden for individual
peers.
The following optional parameters apply to both groups and peers: [External groups only] Describes the number of times that this router
will insert its own AS number when it sends the AS path to an external peer. The default is 1. Higher values are typically used to bias
upstream peers' route selection. (Most routers will prefer to use routes with shorter AS Paths. Using ascount, the AS Path this router
sends can be artificially lengthened.)
Note: ascount supersedes the nov4asloop option. Regardless of whether nov4asloop is set, this router will send multiple copies of
its own AS if the ascount option is set to something greater than 1. Also, if the value of ascount is changed and gated is recon-
figured, routes will not be sent to reflect the new setting. If you want these routes to be sent, restart the peer session by com-
menting out the group ascount, reconfiguring, and then uncommenting and reconfiguring again, or by restarting gated. If a network
is not shared with a peer, gateway specifies a router on an attached network to be used as the next hop router for routes received
from this neighbor. This parameter is usually not needed. Specifies the BGP holdtime value, in seconds, to use when negotiating
the connection with this peer. According to BGP, if gated does not receive a keepalive, update, or notification message within the
period specified in the Hold Time field of the BGP Open message, the BGP connection is closed. The value must be either 0 (no
keepalives will be sent) or at least 3. Some routers, known as route servers, are capable of propagating routes without appending
their own AS to the AS Path. By default, gated drops such routes. Specifying ignorefirstashop on the group clause allows gated to
keep these routes. Use this option only if you are sure that the peers in this group are route servers and not normal routers.
Causes gated to always send keepalives, even when an update could have correctly substituted for one. This allows interoperability
with routers that do not completely obey the protocol specifications on this point. The all parameter retains routes learned from a
peer even if the routes' AS paths contain one of our exported AS numbers. The none parameter (the default) causes gated to disregard
routes containing the router's own AS numbers. Specifies the address to be used on the local end of the TCP connection with the
peer. For external peers, the local address must be on an interface that is shared with the peer or with the peer's gateway when
the gateway parameter is used. A session with an external peer is opened only when an interface with the appropriate local address
(through which the peer or gateway address is directly reachable) is operating.
For other types of peers, a peer session is maintained when any interface with the specified local address is operating. In either
case, incoming connections are recognized as matching a configured peer if they are addressed to the configured local address.
Identifies the autonomous system that gated is representing to this group of peers. The default is that which has been set globally
in the autonomoussystem statement. [Routing groups only] Causes messages to be logged via the syslog mechanism whenever a BGP group
enters or leaves the ESTABLISHED state. By default, any metric (Multi Exit Discriminator) received on a BGP connection is ignored.
If MEDs are used in routing computations, the med option must be specified on the group. By default, MEDs are not sent on external
connections. To send MEDs, use the metric option of the export statement or the metricout option to the peer or group parameter.
If specified, this metric is used as the primary metric on all routes sent to the specified peer(s). This metric overrides the
default metric, a metric specified on the group, and any metric specified by export policy. [Internal and external groups only]
Sets this group's next hops to the router's own address even if it would normally be possible to send a third-party next hop. Using
this option, may cause inefficient routes to be followed, but it may be needed in some cases to deal with broken bridged intercon-
nect media (in cases where the routers on the shared medium do not really have full connectivity to each other) or when other situa-
tions cause broken links. Causes gated to specify the routerid in the aggregator attribute as zero (instead of its routerid) in
order to prevent different routers in an AS from creating aggregate routes with different AS paths. Prevents gated from generating
a default route when EGP receives a valid update from its neighbor. The default route is only generated when the gendefault option
is enabled. Prevents routes with looped AS paths from being advertised to version 4 external peers. This can be useful to avoid
advertising such routes to peer that would incorrectly forward the routes on to version 3 neighbours. Specifies that active OPENs
to this peer should not be attempted. The gated daemon should wait for the peer to issue an open. By default, all explicitly con-
figured peers are active; they periodically send OPEN messages until the peer responds. Specifies the preference used for routes
learned from these peers. This can differ from the default BGP preference set in the bgp statement, so that gated can prefer routes
from one peer, or group of peers, over others. This preference can be explicitly overriden by import policy. In the case of a
preference tie, the second preference, preference2 can be used to break the tie. The default value is 0. Control the amount of
receive and send buffering required of the kernel. The maximum supported is 65535 bytes, although many kernels have a lower limit.
By default, gated configures the maximum supported. These parameters are not needed on normally functioning systems. Forces gated
to issue warning messages when receiving questionable BGP updates, such as duplicate routes or deletions of non-existing routes.
Typically these events are silently ignored. [Routing groups only] Specifies the tracing options for this BGP neighbor. By default
these are inherited from group or BGP global trace options. (See the Trace Options Statement section in gated.conf(4) and the BGP
specific tracing options that follow.) [Routing groups only] By default, gated sets the IP TTL for local peers to one and the TTL
for non-local peers to 255. This option is provided for communicating with improperly functioning routers that ignore packets sent
with a TTL of one. Not all kernels allow the TTL to be specified for TCP connections. By default, gated does not advertise routes
whose AS path is looped (an AS appearing more than once in the path) to version 3 external peers. Setting this flag removes this
constraint. Ignored when set on internal groups or peers. Specifies the version of the BGP protocol to use with this peer. If not
specified, the highest supported version is used first and version negotiation is attempted. If it is specified, only the specified
version is offered during negotiation. Currently supported version are 2, 3, and 4.
The following parameters apply to groups only: Originates the specified AS path attributes. If the attributes are already present, they
may be augmented (as with communities) or possibly replaced (with other attributes that may be supported in the future). Specifies the
amount of time a BGP route must be present before it is accepted into the gated routing database. The default value is 0, meaning that
this feature is disabled. [Routing groups only] Provides a list of interfaces whose routes are carried via the IGP for which third-party
next hops may be used. Specifies the amount of time a route must be present in the gated routing database before it is exported to BGP.
The default value is 0, meaning that this feature is disabled. [Internal, IGP, and routing groups only] Specifies that gated will act as a
route reflector for this group. The no-client-reflect option specifies that gated will not act as an intra-group reflector. [IGP and
routing groups only] Allows BGP's Local_Pref attribute to be used to set the gated preference on reception, and allows gated preference to
set the Local_Pref on transmission. The setpref metric works as a lower limit, below which the imported Local_Pref may not set the gated
preference.
Specifying peers
Within a group, BGP peers can be configured in either of the following ways: explicitly with a peer statement or implicitly with the allow
statement. A description of each is as follows: Configures an individual peer. Each peer inherits all parameters specified on a group as
defaults. Those default can be overridden by parameters explicitly specified on the peer subclause. Allows for peer connections from any
addresses in the specified range of network and mask pairs. All parameters for these peers must be configured on the group clause. The
internal peer structures are created when an incoming open request is received and destroyed when the connection is broken. For more
detail on specifying the network/mask pairs, see the section on Route Filtering in gated.control(4).
Within each group clause, individual peers can be specified or a group of potential peers can be specified using allow. The allow state-
ment is used to specify a set of address masks. If gated receives a BGP connection request from any address in the set specified, it
accepts it and sets up a peer relationship.
BGP Peer parameters
The BGP peer subclause allows the following optional parameters, which can also be specified on the group clause: Normally gated verifies
that incoming packets have an authentication field of all ones. This option can be used to allow communication with an implementation that
uses some other form of authentication.
BGP Tracing options
Note that the state option works with BGP, but does not provide true state transition information.
The following packet tracing options, which can be modified with detail, send, and recv, are supported: Traces all BGP packets. Traces BGP
OPEN packets, which are used to establish a peer relationship. Traces BGP UPDATE packets, which are used to pass network reachability
information. Traces BGP KEEPALIVE packets, which are used to verify peer reachability. traces additions, changes, and deletions to the
gated routing table.
The ICMP Statement
On systems without the BSD routing socket, gated listens to ICMP messages received by the system. Currently, gated processes only ICMP re-
direct packets, but might process additional ICMP messages, such as router discovery messages, in the future. Processing of ICMP redirect
messages is handled by the redirect statement.
Currently, the only reason to specify the icmp statement is to trace the ICMP messages that gated receives.
ICMP Syntax
icmp {
traceoptions trace_options ; } Specifies the tracing options for ICMP. (See the Trace Options Statement section in gated.conf(4) and
the ICMP tracing options that follow.)
ICMP Tracing options
The following packet tracing options, which can be modified with detail and recv, are supported: Traces all ICMP packets received. Traces
only ICMP REDIRECT packets received. Traces only ICMP ROUTER DISCOVERY packets received. Traces only ICMP informational packets, which
include mask request/response, info request/response, echo request/response and time stamp request/response. Traces only ICMP error pack-
ets, which include time exceeded, parameter problem, unreachable and source quench.
Redirect Statement
The redirect code is passed ICMP or ISO redirects learned by monitoring ICMP messages, or via the routing socket on systems that support
it. It processes the redirect request and decides whether to accept the redirect. If the redirect is accepted, a route is installed in
the gated routing table with the protocol redirect. Redirects are deleted from the routing table after 3 minutes.
If gated determines that a redirect is not acceptable, it verifies whether the kernel forwarding table has been modified. On systems where
ICMP messages are monitored, this is accomplished by guessing what the kernel would have done with the redirect. On systems with the rout-
ing socket, the kernel provides an indication of whether the redirect was accepted; gated ignores redirects that were not processed.
If gated has determined that the state of the kernel forwarding table has changed, the necessary requests to the kernel are made to restore
the correct state.
Note: On currently available systems, it is not possible to disable the processing of ICMP redirects, even when the system is functioning
as a router. To ignore the effects of redirects, gated must process each one and actively restore any changes it made to the kernel's
state. Because of the mechanism's involved, there will be windows where the effects of redirects are present in the kernel.
By default, gated removes redirects when actively participating in an interior gateway protocol (RIP or OSPF). It is impossible to enable
redirects once they have been automatically disabled. Listening to RIP in nobroadcast mode does not cause redirects to be ignored, nor
does the use of EGP and BGP. Redirects must be manually configured off in these cases.
Note: In accordance with the latest IETF Router Requirements document, gated insures that all ICMP net redirects are processed as host
redirects. When an ICMP net redirect is accepted, gated issues the requests to the kernel to make sure that the kernel forwarding table is
updated to reflect a host redirect instead of a net redirect.
The redirect statement does not prevent the system from sending redirects, only from listening to them.
Redirect Syntax
redirect yes | no | on | off [{
preference preference ;
interface interface_list
[noredirects] | [redirects] ;
trustedgateways gateway_list ;
traceoptions trace_options ; }] ; Sets the preference for a route learned from a redirect. The default is 30. The interface statement
allows the enabling and disabling of redirects on an interface-by-interface basis. See the Interface List section in gated.conf(4) for the
description of the interface_list. The following parameters are supported: Specifies that redirects received via the specified interface
are ignored. The default is to accept redirects on all interfaces. This is the default. This argument might be necessary when noredirects
is used on a wild card interface descriptor. Defines the list of gateways from which redirects are accepted. The gateway_list is simply a
list of host names or addresses. By default, all routers on the shared network(s) are trusted to supply redirects. But if the trust-
edgateways clause is specified, only redirects from the gateways in the list are accepted. There are no redirect-specific tracing options.
All non-error messages are traced under the normal class.
Redirect Tracing options
There are no redirect-specific tracing options. All non-error messages are traced under the normal class.
The Router Discovery Protocol
The Router Discovery Protocol is an IETF standard protocol used to inform hosts of the existence of routers. It is intended to be used
instead of having hosts wiretap routing protocols such as RIP. It is used in place of, or in addition to, statically configured default
routes in hosts.
The protocol is split into two portions: the server portion, which runs on routers, and the client portion, which runs on hosts. The gated
daemon treats these as two separate protocols, only one of which can be enabled at a time.
The Router Discovery Server
The Router Discovery Server runs on routers and announces their existence to hosts. It does this by periodically multicasting or broad-
casting a Router Advertisement to each interface on which it is enabled. These Router Advertisements contain a list of all the routers
addresses on a given interface and their preference for use as a default router.
Initially these Router Advertisements occur every few seconds, then fall back to every few minutes. In addition, a host might send a
Router Solicitation to which the router responds with a unicast Router Advertisement (unless a multicast or broadcast advertisement is due
momentarily).
Each Router Advertisement contains a Advertisement Lifetime field indicating for how long the advertised addresses are valid. This life-
time is configured such that another Router Advertisement is sent before the lifetime has expired. A lifetime of zero indicates that one
or more addresses are no longer valid.
On systems supporting IP multicasting, the Router Advertisements are by default sent to the all-hosts multicast address 224.0.0.1. How-
ever, the use of broadcast can be specified. When Router Advertisements are sent to the all-hosts multicast address, or an interface is
configured for the limited-broadcast address 255.255.255.255, all IP addresses configured on the physical interface are included in the
Router Advertisement. When the Router advertisements are being sent to a net or subnet broadcast, only the address associated with that
net or subnet is included.
Router Discovery Server Syntax
routerdiscovery server yes | no | on | off [{
traceoptions trace_options ;
interface interface_list
[minadvinterval time]
[maxadvinterval time]
[lifetime time]
;
address interface_list
[advertise] | [ignore]
[broadcast] | [multicast]
[ineligible] | [preference preference]
; }] ; Specifies the Router Discovery tracing options. (See Trace Options Statement section in gated.conf(4) and the Router Dis-
covery specific tracing options.) Specifies the parameters that apply to physical interfaces. Note a slight difference in convention from
the rest of gated: interface specifies just physical interfaces (such as le0, ef0 and en1), while address specifies protocol (in this case,
IP) addresses.
The following interface parameters are supported: The maximum time allowed between sending broadcast or multicast Router Advertise-
ments from the interface. Must be no less than 4 and no more than 30:00 (30 minutes or 1800 seconds). The default is 10:00 (10
minutes or 600 seconds). The minimum time allowed between sending unsolicited broadcast or multicast Router Advertisements from the
interface. Must be no less than 3 seconds and no greater than maxadvinterval. The default is 0.75 * maxadvinterval. The lifetime
of addresses in a Router Advertisement. Must be no less than maxadvinterval and no greater than 2:30:00 (two hours, thirty minutes
or 9000 seconds). The default is 3 * maxadvinterval. Specifies the parameters that apply to the specified set of addresses on
these physical interfaces. Note a slight difference in convention from the rest of gated: interface specifies just physical inter-
faces (such as le0, ef0 and en1), while address specifies protocol (in this case, IP) addresses. Specifies that the specified
address(es) are included in Router Advertisements. This is the default. Specifies that the specified address(es) are not included
in Router Advertisements. Specifies that the given address(es) are included in a broadcast Router Advertisement because this system
does not support IP multicasting, or some hosts on attached network do not support IP multicasting. It is possible to mix addresses
on a physical interface such that some are included in a broadcast Router Advertisement and some are included in a multicast Router
Advertisement. This is the default if the router does not support IP multicasting. Specifies that the given address(es) are
included in a multicast Router Advertisement. If the system does not support IP multicasting, the address(es) are not included. By
default, if the system and given interface support IP multicasting, the address(es) are included in a multicast Router Advertise-
ment. If the interface does not support IP multicasting, the address(es) are included in a broadcast Router Advertisement. The
preferability of the address(es) as a default router address, relative to other router addresses on the same subnet. A 32-bit,
signed, twos-complement integer, with higher values meaning more preferable. Note: hex 80000000 can only be specified as ineligi-
ble. The default is 0. Specifies that the given address(es) are assigned a preference of (hex 80000000), which means that it is
not eligible to be the default route for any hosts.
This is useful when the address(es) should not be used as a default route, but are given as the next hop in an ICMP redirect. This
allows the hosts to verify that the given addresses are up and available.
The Router Discovery Client
A host listens for Router Advertisements via the all-hosts multicast address (224.0.0.2), if IP multicasting is available and enabled, or
on the interface's broadcast address. When starting up, or when reconfigured, a host can send a few Router Solicitations to the all-
routers multicast address, 224.0.0.2, or the interface's broadcast address.
When a Router Advertisement with non-zero lifetime is received, the host installs a default route to each of the advertised addresses. If
the preference is ineligible, or the address is not on an attached interface, the route is marked unusable but retained. If the preference
is usable, the metric is set as a function of the preference such that the route with the best preference is used. If more than one
address with the same preference is received, the one with the lowest IP address will be used. These default routes are not exportable to
other protocols.
When a Router Advertisement with a zero lifetime is received, the host deletes all routes with next-hop addresses learned from that router.
In addition, any routers learned from ICMP redirects pointing to these addresses are deleted. The same happens when a Router Advertisement
is not received to refresh these routes before the lifetime expires.
Router Discovery Client Syntax
routerdiscovery client yes | no | on | off [{
traceoptions trace_options ;
preference preference ;
interface interface_list
[enable] | [disable]
[broadcast] | [multicast]
[quiet] | [solicit]
; }] ; Specifies the tracing options for OSPF. (See the Trace Options Statement section in gated.conf(4) and the OSPF-specific tracing
options that follow.) Specifies the preference of all Router Discovery default routes. The default is 55. Specifies the parameters that
apply to physical interfaces. Note a slight difference in convention from the rest of gated: interface specifies just physical interfaces
(such as le0, ef0 and en1). The Router Discovery Client has no parameters that apply only to interface addresses. Specifies that Router
Discovery should be performed on the specified interface(s). This is the default. Specifies that Router Discovery should not be performed
on the specified interface(s). Specifies that Router Solicitations should be broadcast on the specified interface(s). This is the
default, if IP multicast support is not available on this host or interface. Specifies that Router Solicitations should be multicast on
the specified interface(s). If IP multicast is not available on this host and interface, no solicitation is performed. The default is to
multicast Router Solicitations if the host and interface support it; otherwise, Router Solicitations are broadcast. Specifies that no
Router Solicitations are sent on this interface, even though Router Discovery is performed. Specifies that initial Router Solicitations
are sent on this interface. This is the default.
Router Discovery Tracing options
The Router Discovery Client and Server support the state trace flag, which traces various protocol occurrences. Traces state transitions
The Router Discovery Client and Server do not directly support any packet tracing options; tracing of router discovery packets is enabled
via the ICMP Statement.
The SNMP Statement
The Simple Network Management Protocol (SNMP) is a not a routing protocol but a network management protocol. The snmp statement controls
whether gated tries to contact the SNMP Multiplexing daemon to register supported variables. The SNMP daemon (usually smuxd) must be run
independently. The snmp statement only controls whether gated keeps the management software apprised of its status.
The gated daemon communicates with the SNMP daemon via the SMUX protocol that is described in RFC 1227.
SNMP Syntax
snmp yes | no | on | off [{
port port ;
debug ;
traceoptions traceoptions ; }] ;
Reporting is enabled by specifying yes or on and disabled with no or off. The default is on. Specifies that gated try to contact the SMUX
daemon on a port other than the default port. By default, the SMUX daemon listens for requests on port 199. Enables debugging of the
ISODE SMUX code. The default is debugging disabled. Specifies the tracing options for SMUX. (See the Trace Options Statement section in
gated.conf(4) and the SMUX tracing options that follow.)
SNMP Tracing options
There are no SNMP-specific trace options. SNMP requests received via the SMUX protocol from the SNMP daemon are not handles quite like
packets and are currently handled differently. The detail, send, and recv options are not supported. SNMP requests received from the SMUX
daemon and the associated responses. Protocol requests to register variables. Protocol requests to resolve variable names. SNMP trap
requests from protocols.
The Kernel Statement
While the kernel interface is not technically a routing protocol, it has many characteristics of one, and gated treats it like a routing
protocol. The routes gated chooses to install in the kernel forwarding table are those that are used by the kernel to forward packets.
The add, delete and change operations gated must use to update the typical kernel forwarding table take a significant amount of time. This
does not present a problem for older routing protocols (for example, RIP and EGP), which are not particularly time critical and do not eas-
ily handle very large numbers of routes. The newer routing protocols (for example, OSPF and BGP) have stricter timing requirements and are
often used to process many more routes. The speed of the kernel interface becomes critical when these protocols are used.
To prevent gated from locking up for significant periods of time installing large numbers of routes (up to a minute or more has been
observed on real networks), the processing of these routes is now done in batches. The size of these batches can be controlled by the tun-
ing parameters described below, but normally the default parameters will provide the proper functionality.
During normal shutdown processing, gated normally deletes all the routes it has installed in the kernel forwarding table, except for those
marked with retain. Optionally, gated can leave all routes in the kernel forwarding table by not deleting any routes. In this case,
changes are made to insure that routes with a retain indication are installed in the table. This is useful on systems with large numbers
of routes as it prevents the need to reinstall the routes when gated restarts. This can greatly reduce the time it takes to recover from a
restart.
Forwarding tables and Routing tables
The table in the kernel that controls the forwarding of packets is a forwarding table (referred to in ISO as a forwarding information base,
or FIB). The table that gated uses internally to store routing information it learns from routing protocols is a routing table (referred
to in ISO as a routing information base, or RIB). The routing table is used to collect and store routes from various protocols. For each
unique combination of network and mask, an active route is chosen; this route is the one with the best (numerically smallest) preference.
All the active routes are installed in the kernel forwarding table. The entries in this table are what the kernel actually uses to forward
packets.
Updating the Forwarding Table
There are two main methods of updating the kernel FIB: the ioctl() interface and the routing socket interface. Their various characteris-
tics are described as follows:
Updating the Forwarding Table with the ioctl interface
The ioctl interface to the forwarding table was introduced in BSD 4.3 and widely distributed in BSD 4.3. This is a one-way interface; it
allows gated to update the kernel forwarding table only. It has the following limitations: The BSD 4.3 networking code assumed that all
subnets of a given network had the same subnet mask. This limitation is enforced by the kernel. The network mask is not stored in the
kernel forwarding table, but determined when a packet is forwarded by searching for interfaces on the same network. The gated daemon is
able to update the kernel forwarding table, but it is not aware of other modifications of the forwarding table. The gated daemon is able
to listen to ICMP messages and determine how the kernel has updated the forwarding table in response to ICMP redirects. The gated daemon
is not able to detect changes to the forwarding table resulting from the use of the the route command by the system administrator. Use of
the route command on systems that use the ioctl() interface is strongly discouraged while gated is running. In all known implementations,
there is no change operation supported. To change a route that exists in the kernel, the route must be deleted and a new one added.
Updating the Forwarding Table with the routing socket interface
The routing socket interface to the kernel forwarding table was introduced in BSD 4.3 Reno, widely distributed in BSD 4.3 Net/2 and
improved in BSD 4.4. This interface is simply a socket, similar to a UDP socket, on which the kernel and gated exchange messages. It has
the following advantages over the ioctl() interface: The network mask is passed to the kernel explicitly. This allows different masks to
be used on subnets of the same network. It also allows routes with masks that are more general than the natural mask to be used. This is
known as classless routing. Not only is gated able to change the kernel forwarding table with this interface, but the kernel can also
report changes to the forwarding table to gated. The most interesting of these is an indication that a redirect has modified the kernel
forwarding table; this means that gated no longer needs to monitor ICMP messages to learn about redirects. Plus, there is an indication of
whether the kernel processed the redirect; gated can safely ignore redirect messages that the kernel did not process. Changes to the rout-
ing table by other processes, including the route command are received via the routing socket. This allows gated to insure that the kernel
forwarding table is synchronized with the routing table. Plus it allows the system administrator the ability to do some operations with
the route command while gated is running. There is a functioning change message that allows routes in the kernel to be atomically changed.
Some early versions of the routing socket code had bugs in the change message processing. There are compilation time and configuration
time options that cause delete and add sequences to be used in lieu of change messages. New levels of kernel/gated communications can be
added by adding new message types.
Reading the Forwarding Table
When gated starts up, it reads the kernel forwarding table and installs corresponding routes in the routing table. These routes are called
remnants, and are timed out after a configured interval (which defaults to 3 minutes), or as soon as a more attractive route is learned.
This allows forwarding to occur during the time it takes the routing protocols to start learning routes.
The following methods are used for reading the forwarding table from the kernel:
Reading forwarding table via kmem
On Tru64 UNIX systems, gated reads the forwarding table via kmem at boot time. After the system is booted, gated uses the Routing Socket
interface to receive updates from the kernel.
Reading the forwarding table via OS specific methods
Some operating systems define their own method of reading the kernel forwarding table.
Reading the interface list
The kernel support subsystem of gated is responsible for reading the status of the kernel's physical and protocol interfaces periodically.
The gated daemon detects changes in the interface list and notifies the protocols so they can start or stop instances or peers. The inter-
face list is read in the following ways:
Reading the interface list with SIOCGIFCONF
On systems based on BSD 4.3, 4.3 Reno, and 4.3 Net/2, the SIOCGIFCONF ioctl interface is used to read the kernel interface list. Using
this method, a list of interfaces and some basic information about them is returned by the SIOCGIFCONF call. Other information must be
learned by issuing other ioctls to learn the interface network mask, flags, MTU, metric, destination address (for point-to-point inter-
faces) and broadcast address (for broadcast capable interfaces).
The gated daemon rereads this list every 15 second looking for changes. When the routing socket is in use, the daemon also rereads it
whenever a message is received indicating a change in routing configuration. Receipt of a SIGUSR2 signal also causes gated to reread the
list. This interval can be explicitly configured in the interface configuration.
Reading the interface list with sysctl
BSD 4.4 added the ability to read the kernel interface list via the sysctl system call. The interface status is returned atomically as a
list of routing socket messages that gated parses for the required information.
BSD 4.4 also added routing socket messages to report interface status changes immediately. This allows gated to react quickly to changes
in interface configuration.
When this method is used, gated rereads the interface list only once a minute. It also rereads the list on routing table change indica-
tions and when a SIGUSR2 is received. This interval can be explicitly configured in the interface configuration.
Reading interface physical addresses
Later versions of the getkerninfo() and sysctl() interfaces return the interface physical addresses as part of the interface information.
On most systems where this information is not returned, gated scans the kernel physical interface list for this information for interfaces
with IFF_BROADCAST set, assuming that their drivers are handled the same as Ethernet drivers. On some systems, system specific interfaces
are used to learn this information.
The interface physical addresses are useful for IS-IS. For IP protocols, they are not currently used, but might be in the future.
Reading kernel variables
At startup, gated reads some special variables out of the kernel. This is usually done with the nlist (or kvm_nlist) system call, but some
systems use different methods.
The variables read include the status of UDP checksum creation and generation, IP forwarding, and kernel version (for informational pur-
poses). On systems where the routing table is read directly from kernel memory, the root of the hash table or radix tree routing table is
read. On systems where interface physical addresses are not supplied by other means, the root of the interface list is read.
Special route flags
The later BSD-based kernels support the following special route flags: Instead of forwarding a packet like a normal route, routes with
RTF_REJECT cause packets to be dropped and unreachable messages to be sent to the packet originators. This flag is valid only on routes
pointing at the loopback interface. Like the RTF_REJECT flag, routes with RTF_BLACKHOLE cause packets to be dropped, but unreachable mes-
sages are not sent. This flag is valid only on routes pointing at the loopback interface. When gated starts, it reads all the routes cur-
rently in the kernel forwarding table. Besides interface routes, it usually marks everything else as a remnant from a previous run of
gated and deletes it after a few minutes. This means that routes added with the route command are not retained after gated has started.
To fix this, the RTF_STATIC flag was added. When the route command is used to install a route that is not an interface route, it
sets the RTF_STATIC flag. This signals gated that said route was added by the system administrator and should be retained.
Kernel Syntax
kernel {
options
[nochange]
[noflushatexit]
;
routes number ;
flash
[limit number]
[type interface | interior | all]
;
background
[limit number]
[priority flash | higher | lower]
;
traceoptions trace_options ; } ; Configures kernel options. The following options are valid: On systems supporting the routing socket,
this insures that changes operations are not performed, only deletes and adds. This is useful on early versions of the routing socket code
where the change operation was broken. During normal shutdown processing, gated deletes all routes from the kernel forwarding table that
do not have a retain indication. The noflushatexit option prevents route deletions at shutdown. Instead, routes are changed and added to
make sure that all the routes marked with retain get installed.
This is handy on systems with thousands of routes. Upon startup, gated notices which routes are in the kernel forwarding table and
does not add them back. On some systems, kernel memory is scarce. This parameter limits the maximum number of routes gated
installs in the kernel. Normally, gated adds, changes, or deletes routes in interface, internal, or external order; that is, it
queues interface routes first, followed by internal routes, followed by external routes, and processes the queue from the beginning.
If this parameter is specified and the limit is hit, gated does two scans of the list instead. On the first scan it does deletes,
and also deletes all changed routes, turning the queued changes into adds. It then rescans the list, adding routes in inter-
face/internal/external order until it hits the limit again. This tends to favor internal routes over external routes. The default
is to not limit the number of routes in the kernel forwarding table. When routes change, the process of notifying the protocols is
called a flash update. The kernel forwarding table interface is the first to be notified. Normally a maximum of 20 interface
routes can be processed during one flash update. The flash command allows tuning of the following parameters: Specifies the maximum
number of routes that can be processed during one flash update. The default is 20. A value of -1 causes all pending route changes
of the specified type to be processed during the flash update. Specifies the type of routes that are processed during a flash
update. Interior specifies that interior routes (See the definition of interior gateway protocols) are also installed. The all
parameter specifies the inclusion of exterior routes (See the definition of exterior gateway protocols) as well. The default is
interface, which specifies that only interface routes is installed during a flash update.
Specifying flash limit -1 all causes all routes to be installed during the flash update; this mimics the behavior of previous ver-
sions of gated. Since only interface routes are normally installed during a flash update, the remaining routes are processed in
batches in the background, that is, when no routing protocol traffic is being received. Normally, 120 routes are installed at a
time to allow other tasks to be performed and this background processing is done at lower priority than flash updates. The follow-
ing parameters allow tuning of these parameters: Specifies the number of routes that can be processed at during one batch. The
default is 120. Specifies the priority of the processing of batches of kernel updates in relationship to the flash update process-
ing. The default is lower, which means that flash updates are processed first. To process kernel updates at the same priority as
flash updates, specify flash; to process them at a lower priority, use lower.
Kernel Interface Tracing options
While the kernel interface is not a routing protocol, in many cases it is handled as one. The following two symbols make sense when
entered from the command line since the code that uses them is executed before the trace file is parsed.
Symbols read from the kernel, by nlist(), or similar interface. Interface list scan. This option is useful when entered from the command
line as the first interface list scan is performed before the configuration file is parsed.
The following tracing options can only be specified in the configuration file. They are not valid from the command line. Traces routes
read from the kernel when gated starts. Traces requests by gated to Add/Delete/Change routes in the kernel forwarding table.
The following general option and packet-tracing options only apply on systems that use the routing socket to exchange routing information
with the kernel. They do not apply on systems that use the old BSD4.3 ioctl() interface to the kernel. Informational messages received
from the routing socket, such as TCP loss, routing lookup failure, and route resolution requests. The gated daemon does not currently do
processing on these messages, just logs the information if requested.
The following packet tracing options, which can be modified with detail, send, and recv, are supported: Routes exchanged with the kernel,
including Add/Delete/Change messages and Add/Delete/Change messages received from other processes. Redirect messages received from the
kernel. Interface status messages received from the kernel. These are only supported on systems with networking code derived from BSD
4.4. Other messages received from the kernel, including those mentioned in the info type above.
Static Routes Statements
The static statements define the static routes used by gated. A single static statement can specify any number routes. The static state-
ments occur after protocol statements and before control statements in the gated.conf file. Any number of static statements can be speci-
fied, each containing any number of static route definitions. These routes can be overridden by routes with better preference values.
Static Syntax
static {
(host host) | default |
(network [(mask mask) | (masklen number)])
gateway gateway_list
[interface interface_list]
[preference preference]
[retain]
[reject]
[blackhole]
[noinstall] ;
(network [(mask mask) | (masklen number)])
interface interface
[preference preference]
[retain]
[reject]
[blackhole]
[noinstall] ; } ; This is the most general form of the static statement. It defines a static route through one or more gateways.
Static routes are installed when one or more of the gateways listed are available on directly attached interfaces. If more than one eligi-
ble gateways are available, they are limited by the number of multipath destinations supported (this compile time parameter is currently
almost always one on Unix).
The following parameters for static routes are supported: When this parameter is specified, gateways are only considered valid when
they are on one of these interfaces. See the section on interface list specification for the description of the interface_list.
Selects the preference of this static route. The preference controls how this route competes with routes from other protocols. The
default preference is 60. Prevents specific static routes from being removed. Normally, gated removes all routes except interface
routes from the kernel forwarding table during a graceful shutdown. This is useful to insure that some routing is available when
gated is not running. Installs this route as a reject route. Instead of forwarding a packet like a normal route, reject routes
cause packets to be dropped and unreachable messages to be sent to the packet originators. Not all kernel forwarding engines sup-
port reject routes. A blackhole route is the same as a reject route except that unreachable messages are not supported. Normally,
the route with the lowest preference is installed in the kernel forwarding table and is the route exported to other protocols. When
noinstall is specified on a route, it is not installed in the kernel forwarding table when it is active, but it will still be eligi-
ble to be exported to other protocols. This form defines a static interface route that is used for primitive support of multiple
network addresses on one interface. The preference, retain, reject, blackhole, and noinstall options are the same as described pre-
viously.
RELATED INFORMATION
Daemons: gated(8).
Files: gated.conf(4), gated.control(4).
Networking: gated_intro(7).
RFC 827, Exterior Gateway Protocol EGP, E. Rosen.
RFC 891, DCN local-network protocols, D. Mills.
RFC 904, Exterior Gateway Protocol Formal Specification, D. Mills.
RFC 1058, Routing Information Protocol, C. Hedrick.
RFC 1105, Border Gateway Protocol BGP, K. Lougheed, Y. Rekhter.
RFC 1163, A Border Gateway Protocol (BGP), K. Lougheed, Y. Rekhter.
RFC 1164, Application of the Border Gateway Protocol in the Internet, J. Honig, D. Katz, M. Mathis, Y. Rekhter, J. Yu.
RFC 1227, SNMP MUX Protocol and MIB, M. Rose.
RFC 1245, OSPF Protocol Analysis, J. Moy.
RFC 1246, Experience with the OSPF Protocol, J. Moy.
RFC 1253, OSPF Version 2 Management Information Base, F. Baker, R. Coltun.
RFC 1256, ICMP Router Discovery Messages, S. Deering.
RFC 1265, BGP Protocol Analysis, Y. Rekhter.
RFC 1266, Experience with the BGP Protocol, Y. Rekhter.
RFC 1267, A Border Gateway Protocol 3 (BGP-3), K. Lougheed, Y. Rekhter.
RFC 1268, Application of the Border Gateway Protocol in the Internet, P. Gross, Y. Rekhter.
RFC 1269, Definitions of Managed Objects for the Border Gateway Protocol (Version 3), J. Burruss, S. Willis.
RFC 1321, The MD5 Message-Digest Algorithm, R. Rivest.
RFC 1370, Internet Architecture Board Applicability Statement for OSPF
RFC 1388, RIP Version 2 Carrying Additional Information, G. Malkin.
RFC 1397, Default Route Advertisement In BGP2 And BGP3 Versions Of The Border Gateway Protocol, D. Haskin.
RFC 1403, BGP OSPF Interaction, K. Varadhan.
RFC 1583, OSPF Version 2, J. Moy. delim off
gated.proto(4)