routed - network routing daemon
/etc/routed [ -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 kernel routing table entries.
In normal operation routed listens on udp(4P) socket 520 (decimal) for
routing information packets. If the host is an internetwork router, it
periodically supplies copies of its routing tables to any directly con-
nected hosts and networks.
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 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
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 rela-
tive 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 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
When an update is applied, routed records the change in its internal
tables and generates a response packet to all directly connected hosts
and networks. Routed waits a short period of time (no more than 30
seconds) before modifying the kernel's routing tables to allow possible
unstable situations to settle.
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 dele-
tion. Deletions are delayed an additional 60 seconds to insure the
invalidation is propagated throughout the internet.
Hosts acting as internetwork routers gratuitously supply their routing
tables every 30 seconds to all directly connected hosts and networks.
Supplying the -s option forces routed to supply routing information
whether it is acting as an internetwork router or not. The -q option
is the opposite of the -s option. If the -t option is specified, all
packets sent or received are printed on the standard output. In addi-
tion, 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 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 identified using 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 main-
tained 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 informa-
tion is distributed to the gateway and if no routing information is
received for a period of the time, the associated route is deleted.
The /etc/gateways is comprised of a series of lines, each in the fol-
< net | host > name1 gateway name2 metric value < passive | active >
The net or host keyword indicates if the route is to a network or spe-
Name1 is the name of the destination network or host. This may be a
symbolic name located in /etc/networks or /etc/hosts, or an Internet
address specified in ``dot'' notation; see inet(3N).
Name2 is the name or address of the gateway to which messages should be
Value is a metric indicating the hop count to the destination host or
The keyword passive or active indicates if the gateway should be
treated as passive or active (as described above).
/etc/gateways for distant gateways
``Internet Transport Protocols'', XSIS 028112, Xerox System Integration
The kernel's routing tables may not correspond to those of routed for
short periods of time while processes utilizing existing routes exit;
the only remedy for this is to place the routing process in the kernel.
Routed should listen to intelligent interfaces, such as an IMP, and to
error protocols, such as ICMP, to gather more information.
4th Berkeley Distribution 3 February 1983 ROUTED(8C)