ROUTED(8) MachTen Programmer’s Manual ROUTED(8)

NAME
routed - network routing daemon

SYNOPSIS
routed [ -d ] [ -g ] [ -s ] [ -q ] [ -t ] [ logfile ]

DESCRIPTION
Routed is invoked at boot time to manage the network rout-
ing tables. The routing daemon uses a variant of the
Xerox NS Routing Information Protocol 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 clus-
ter of networks.

In normal operation routed listens on the udp(4) socket
for the route service (see services(5)) for routing infor-
mation 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 inter-
face is ignored). If multiple interfaces are present, it
is assumed that the host will forward packets between net-
works. Routed then transmits a request packet on each
interface (using a broadcast packet if the interface sup-
ports 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 met-
ric relative to the sender.

Response packets received by routed are used to update the
routing tables if one of the following conditions is sat-
isfied:

(1) No routing table entry exists for the destination
network or host, and the metric indicates the des-
tination 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 sec-
onds) 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 com-
pared 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 met-
ric is set to infinity and marked for deletion. Deletions
are delayed an additional 60 seconds to insure the invali-
dation is propagated throughout the local internet.

Hosts acting as internetwork routers gratuitously supply
their routing tables every 30 seconds to all directly con-
nected 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 rout-
ing 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 avail-
able.

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 rout-
ing information whether it is acting as an inter-
network router or not. This is the default if mul-
tiple 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 sup-
ports the notion of ‘‘distant’’ passive and active gate-
ways. 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. Gate-
ways 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 pro-
cess 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 exter-
nal entries is to inform routed that another routing pro-
cess 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 mes-
sages should be forwarded.

Value is a metric indicating the hop count to the destina-
tion 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. Sites needing assistance with
such configurations should contact the Computer Systems
Research Group at Berkeley.

FILES
/etc/gateways for distant gateways

SEE ALSO
‘‘Internet Transport Protocols’’, XSIS 028112, Xerox Sys-
tem Integration Standard.
udp(4), icmp(4), XNSrouted(8), htable(8)

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
Xerox NS (XNSrouted(8)) and 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).

MachTen June 24, 1990 4