routed [-d] [-g] [-q] [-s] [-t] [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 Proto
col 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 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 inter
faces are present, it is assumed that the host will forward packets be
tween 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 gen
erated contains a list of known routes, each marked with a ``hop count''
metric (a count of 16, or greater, is considered ``infinite''). The met
ric 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 ex
isting 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 ta
bles 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
on each network is used to determine that the network and interface are
functioning correctly. If no response is received on an interface, an
other 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'' destination. 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 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 di
vorce 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 his
tory 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 ex
change routing information, while gateways marked active should be will
ing to exchange routing information (i.e. they should have a routed pro
cess running on the machine). Routes through passive gateways are in
stalled in the kernel's routing tables once upon startup. Such routes
are not included in any routing information transmitted. Active gateways
are treated equally to network interfaces. Routing information is dis
tributed 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 en
tries is to inform routed that another routing process will install such
a route, and that alternate routes to that destination should not be in
stalled. 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 follow
ing format:
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 informa
tion 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.
FILES
/etc/gateways for distant gateways
SEE ALSO
udp(7), icmp(7)
Internet Transport Protocols, XSIS 028112, Xerox System Integration
Standard.
BUGS
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 re
ceived by reading the ICMP packets received via a raw socket.
Routed should incorporate other routing protocols. Using separate pro
cesses for each requires configuration options to avoid redundant or com
peting 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 output side fails).
HISTORY
The routed command appeared in 4.2BSD.
Linux NetKit (0.17) December 11, 1993 3
Man(1) output converted with
man2html