ROUTED(8) BSD System Manager's Manual ROUTED(8)
routed -- network routing daemon
routed [-d] [-g] [-q] [-s] [-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 kernel
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 networks.
In normal operation routed listens on the udp(4) socket for the route(8) service (see
services(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 net-
When routed is started, it uses the SIOCGIFCONF ioctl(2) 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 main-
tained 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
Response packets received by routed are used to update the routing tables if one of the fol-
lowing conditions is satisfied:
1. No routing table entry exists for the destination network or host, and the metric indi-
cates 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 table
entry. That is, updated information is being received from the very internetwork
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 ta-
ble 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 sec-
onds to all directly connected hosts and networks. The response is sent to the broadcast
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 network 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.
Options supported by routed:
-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'' desti-
nation. 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 routers.
-s Supplying this option forces routed to supply routing information whether it is act-
ing 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 stan-
dard output. In addition, routed will not divorce itself from the controlling ter-
minal 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(2).
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).
Routes through passive gateways are installed in the kernel's routing tables once upon
startup. Such routes are not included in any routing information transmitted. Active gate-
ways are treated equally to network interfaces. Routing information is distributed to the
gateway and if no routing information is received for a period of time, the associated route
is deleted. Gateways marked external 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.
/etc/gateways for distant gateways
Internet Transport Protocols, XSIS 028112, Xerox System Integration Standard.
routed is of dubious value. Consider using gated(8) or zebra(8).
The kernel's routing tables may not correspond to those of routed when redirects change or
add routes. Routed should note any redirects received by reading the ICMP packets received
via a raw socket.
Routed should incorporate other routing protocols. Using separate processes for each
requires configuration options to avoid redundant or competing routes.
Routed should listen to intelligent interfaces, such as an IMP, to gather more information.
It does not always detect unidirectional failures in network interfaces (e.g., when the out-
put side fails).
The routed command appeared in 4.2BSD.
Linux NetKit (0.17) December 11, 1993 Linux NetKit (0.17)