routed - network routing daemon
routed [ -d ] [ -g ] [ -s ] [ -q ] [ -t ] [ logfile ]
Routed is invoked at boot time to manage the network routing tables. The routing daemon
uses a variant of the Xerox NS Routing Information Protocol in maintaining up to date ker-
nel routing table entries. It used a generalized protocol capable of use with multiple
address types, but is currently used only for Internet routing within a cluster of net-
In normal operation routed listens on the udp(4) socket for the route service (see ser-
vices(5)) for routing information packets. If the host is an internetwork router, it
periodically supplies copies of its routing tables to any directly connected hosts and
When routed is started, it uses the SIOCGIFCONF ioctl to find those directly connected
interfaces configured into the system and marked ``up'' (the software loopback interface
is ignored). If multiple interfaces are present, it is assumed that the host will forward
packets between networks. Routed then transmits a request packet on each interface (using
a broadcast packet if the interface supports it) and enters a loop, listening for request
and response packets from other hosts.
When a request packet is received, routed formulates a reply based on the information
maintained in its internal tables. The response packet generated contains a list of known
routes, each marked with a ``hop count'' metric (a count of 16, or greater, is considered
``infinite''). The metric associated with each route returned provides a metric relative
to the sender.
Response packets received by routed are used to update the routing tables if one of the
following conditions is satisfied:
(1) No routing table entry exists for the destination network or host, and the metric
indicates the destination is ``reachable'' (i.e. the hop count is not infinite).
(2) The source host of the packet is the same as the router in the existing routing ta-
ble entry. That is, updated information is being received from the very internet-
work router through which packets for the destination are being routed.
(3) The existing entry in the routing table has not been updated for some time (defined
to be 90 seconds) and the route is at least as cost effective as the current route.
(4) The new route describes a shorter route to the destination than the one currently
stored in the routing tables; the metric of the new route is compared against the
one stored in the table to decide this.
When an update is applied, routed records the change in its internal tables and updates
the kernel routing table. The change is reflected in the next response packet sent.
In addition to processing incoming packets, routed also periodically checks the routing
table entries. If an entry has not been updated for 3 minutes, the entry's metric is set
to infinity and marked for deletion. Deletions are delayed an additional 60 seconds to
insure the invalidation is propagated throughout the local internet.
Hosts acting as internetwork routers gratuitously supply their routing tables every 30
seconds to all directly connected hosts and networks. The response is sent to the broad-
cast address on nets capable of that function, to the destination address on point-to-
point links, and to the router's own address on other networks. The normal routing tables
are bypassed when sending gratuitous responses. The reception of responses on each net-
work is used to determine that the network and interface are functioning correctly. If no
response is received on an interface, another route may be chosen to route around the
interface, or the route may be dropped if no alternative is available.
Routed supports several options:
-d Enable additional debugging information to be logged, such as bad packets received.
-g This flag is used on internetwork routers to offer a route to the ``default'' des-
tination. This is typically used on a gateway to the Internet, or on a gateway
that uses another routing protocol whose routes are not reported to other local
-s Supplying this option forces routed to supply routing information whether it is
acting as an internetwork router or not. This is the default if multiple network
interfaces are present, or if a point-to-point link is in use.
-q This is the opposite of the -s option.
-t If the -t option is specified, all packets sent or received are printed on the
standard output. In addition, routed will not divorce itself from the controlling
terminal so that interrupts from the keyboard will kill the process.
Any other argument supplied is interpreted as the name of file in which routed's actions
should be logged. This log contains information about any changes to the routing tables
and, if not tracing all packets, a history of recent messages sent and received which are
related to the changed route.
In addition to the facilities described above, routed supports the notion of ``distant''
passive and active gateways. When routed is started up, it reads the file /etc/gateways
to find gateways which may not be located using only information from the SIOGIFCONF
ioctl. Gateways specified in this manner should be marked passive if they are not
expected to exchange routing information, while gateways marked active should be willing
to exchange routing information (i.e. they should have a routed process running on the
machine). Passive gateways are maintained in the routing tables forever and information
regarding their existence is included in any routing information transmitted. Active
gateways are treated equally to network interfaces. Routing information is distributed to
the gateway and if no routing information is received for a period of the time, the asso-
ciated route is deleted. External gateways are also passive, but are not placed in the
kernel routing table nor are they included in routing updates. The function of external
entries is to inform routed that another routing process will install such a route, and
that alternate routes to that destination should not be installed. Such entries are only
required when both routers may learn of routes to the same destination.
The /etc/gateways is comprised of a series of lines, each in the following format:
< net | host > name1 gateway name2 metric value < passive | active | external >
The net or host keyword indicates if the route is to a network or specific host.
Name1 is the name of the destination network or host. This may be a symbolic name located
in /etc/networks or /etc/hosts (or, if started after named(8), known to the name server),
or an Internet address specified in ``dot'' notation; see inet(3).
Name2 is the name or address of the gateway to which messages should be forwarded.
Value is a metric indicating the hop count to the destination host or network.
One of the keywords passive, active or external indicates if the gateway should be treated
as passive or active (as described above), or whether the gateway is external to the scope
of the routed protocol.
Internetwork routers that are directly attached to the Arpanet or Milnet should use the
Exterior Gateway Protocol (EGP) to gather routing information rather then using a static
routing table of passive gateways. EGP is required in order to provide routes for local
networks to the rest of the Internet system. Sites needing assistance with such configu-
rations should contact the Computer Systems Research Group at Berkeley.
/etc/gateways for distant gateways
``Internet Transport Protocols'', XSIS 028112, Xerox System Integration Standard.
udp(4), XNSrouted(8), htable(8)
The kernel's routing tables may not correspond to those of routed when redirects change or
add routes. The only remedy for this is to place the routing process in the kernel.
Routed should incorporate other routing protocols, such as Xerox NS (XNSrouted(8)) and
EGP. Using separate processes for each requires configuration options to avoid redundant
or competing routes.
Routed should listen to intelligent interfaces, such as an IMP, and to error protocols,
such as ICMP, to gather more information. It does not always detect unidirectional fail-
ures in network interfaces (e.g., when the output side fails).
4.2 Berkeley Distribution November 17, 1996 ROUTED(8)