routed(1M) UNIX System V(Internet Utilities) routed(1M)
NAME
routed - network routing daemon
SYNOPSIS
in.routed [ -qstv ] [ logfile ]
DESCRIPTION
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
connected hosts and networks.
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 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.
request 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 (that is, 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.
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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 deletion.
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
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 a history of recent messages sent and
received which are related to the changed route. The -v option allows a
logfile to be created showing the changes made to the routing tables with
a timestamp.
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 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 (that is, 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 associated
route is deleted.
The gateways is comprised of a series of lines, each in the following
format:
< net | host > filename1 gateway filename2 metric value < passive |
active >
The net or host keyword indicates if the route is to a network or
specific host.
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routed(1M) UNIX System V(Internet Utilities) routed(1M)
filename1 is the name of the destination network or host. This may be a
symbolic name located in networks or hosts, or an Internet address
specified in dot notation; see inet(3N).
filename2 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.
The keyword passive or active indicates if the gateway should be treated
as passive or active (as described above).
FILES
/etc/gateways for distant gateways
/etc/networks
/etc/hosts
SEE ALSO
ioctl(2), inet(7), udp(7)
NOTES
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.
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