NAME
routed - network routing daemon

SYNOPSIS
/etc/routed [ -d ] [ -g ] [ -s ] [ -q ] [ -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 Protocol in maintaining up to date kernel routing table
entries. It uses 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(4P) socket for the
route 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 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 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.

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 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 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.

Routed supports several options:

-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 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 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. 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
distributed to the gateway and if no routing information is
received for a period of the 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.

FILES
/etc/gateways for distant gateways

SEE ALSO
"Internet Transport Protocols", XSIS 028112, Xerox System
Integration Standard.
udp(4), icmp(4)

BUGS
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, such as EGP.
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 output side fails).