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 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
between networks. Routed then transmits a request packet on each inter-
face (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
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 decide
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 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
-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
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 his-
tory of recent messages sent and received which are related to the
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 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
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 follow-
<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 sym-
bolic 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
Value is a metric indicating the hop count to the destination host or
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.
/etc/gateways for distant gateways
Internet Transport Protocols, XSIS 028112, Xerox System Integration
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 pro-
cesses for each requires configuration options to avoid redundant or com-
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).
The routed command appeared in 4.2BSD.
Linux NetKit (0.17) December 11, 1993 Linux NetKit (0.17)
Man(1) output converted with