ROUTED(8) BSD System Manager's Manual ROUTED(8)
NAME
routed -- network RIP and router discovery routing daemon
SYNOPSIS
routed [-sqdghmpAt] [-T tracefile] [-F net[/mask[,metric]]]
DESCRIPTION
Routed is a daemon invoked at boot time to manage the network routing tables. It uses Routing Informa-tion Information
tion Protocol, RIPv1 (RFC 1058), RIPv2 (RFC 1723), and Internet Router Discovery Protocol (RFC 1256) to
maintain the kernel routing table. The RIPv1 protocol is based on the reference 4.3BSD daemon.
It listens on the udp(4) socket for the route(8) service (see services(5)) for Routing Information Pro-tocol Protocol
tocol packets. It also sends and receives multicast Router Discovery ICMP messages. If the host is a
router, routed periodically supplies copies of its routing tables to any directly connected hosts and
networks. It also advertise or solicits default routes using Router Discovery ICMP messages.
When started (or when a network interface is later turned on), routed uses an AF_ROUTE address family
facility to find those directly connected interfaces configured into the system and marked "up". It
adds necessary routes for the interfaces to the kernel routing table. Soon after being first started,
and provided there is at least one interface on which RIP has not been disabled, routed deletes all
pre-existing non-static routes in kernel table. Static routes in the kernel table are preserved and
included in RIP responses if they have a valid RIP metric (see route(8) ).
If more than one interface is present (not counting the loopback interface), it is assumed that the
host should forward packets among the connected networks. After transmitting a RIP request and Router
Discovery Advertisements or Solicitations on a new interface, the daemon enters a loop, listening for
RIP request and response and Router Discover 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"). Advertised metrics reflect the
metric associated with interface (see ifconfig(8) ), so setting the metric on an interface is an effec-tive effective
tive way to steer traffic.
Responses do not contain routes with a first hop on the requesting network to implement in part
split-horizon.
The routing table maintained by the daemon includes space for several gateways for each destination to
speed recovery from a failing router. RIP response packets received are used to update the routing
tables provided they are from one of the several currently recognized gateways or advertise a better
metric than at least one of the existing gateways.
When an update is applied, routed records the change in its own tables and updates the kernel routing
table if the best route to the destination changes. The change in the kernel routing table is
reflected in the next batch of response packets sent. If the next response is not scheduled for a
while, a flash update response containing only recently changed routes is 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 until the route has been advertised with an infinite metric to insure
the invalidation is propagated throughout the local internet. This is a form of poison reverse.
Routes in the kernel table that are added or changed as a result of ICMP Redirect messages are deleted
after a while to minimize black-holes. When a TCP connection suffers a timeout, the kernel tells
routed, which deletes all redirected routes through the gateway involved, advances the age of all RIP
routes through the gateway to allow an alternate to be chosen, and advances of the age of any relevant
Router Discovery Protocol default routes.
Hosts acting as internetwork routers gratuitously supply their routing tables every 30 seconds to all
directly connected hosts and networks. These RIP responses are sent to the broadcast address on nets
that support broadcasting, to the destination address on point-to-point links, and to the router's own
address on other networks. If RIPv2 is enabled, multicast packets are sent on interfaces that support
multicasting.
If no response is received on a remote interface, if there are errors while sending responses, or if
there are more errors than input or output (see netstat(8) ), then the cable or some other part of the
interface is assumed to be disconnected or broken, and routes are adjusted appropriately.
The Internet Router Discovery Protocol is handled similarly. When the daemon is supplying RIP routes,
it also listens for Router Discovery Solicitations and sends Advertisements. When it is quiet and only
listening to other RIP routers, it sends Solicitations and listens for Advertisements. If it receives
a good Advertisement, it stops listening for broadcast or multicast RIP responses. It tracks several
advertising routers to speed recovery when the currently chosen router dies. If all discovered routers
disappear, the daemon resumes listening to RIP responses.
While using Router Discovery (which happens by default when the system has a single network interface
and a Router Discover Advertisement is received), there is a single default route and a variable number
of redirected host routes in the kernel table.
The Router Discover standard requires that advertisements have a default "lifetime" of 30 minutes.
That means should something happen, a client can be without a good route for 30 minutes. It is a good
idea to reduce the default to 45 seconds using -P rdisc_interval=45 on the command line or
rdisc_interval=45 in the /etc/gateways file.
See the pm_rdisc facility described below to support "legacy" systems that can handle neither RIPv2 nor
Router Discovery.
By default, neither Router Discovery advertisements nor solicitations are sent over point to point
links (e.g. PPP).
Options supported by routed:
-s this option forces routed to supply routing information. This is the default if multiple net-work network
work interfaces are present on which RIP or Router Discovery have not been disabled, and if the
kernel switch ipforwarding=1.
-q is the opposite of the -s option.
-d Do not run in the background. This option is meant for interactive use.
-g This flag is used on internetwork routers to offer a route to the "default" destination. It is
equivalent to -F 0/0,1 and is present mostly for historical reasons. A better choice is -P
pm_rdisc on the command line or pm_rdisc in the /etc/gateways file. since a larger metric will
be used, reducing the spread of the potentially dangerous default route. 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. Notice that because a metric of 1 is used,
this feature is dangerous. It is more commonly accidently used to create chaos with routing
loop than to solve problems.
-h This causes host or point-to-point routes to not be advertised, provided there is a network
route going the same direction. That is a limited kind of aggregation. This option is useful
on gateways to ethernets that have other gateway machines connected with point-to-point links
such as SLIP.
-m This causes the machine to advertise a host or point-to-point route to its primary interface.
It is useful on multi-homed machines such as NFS servers. This option should not be used
except when the cost of the host routes it generates is justified by the popularity of the
server. It is effective only when the machine is supplying routing information, because there
is more than one interface. The -m option overrides the -q option to the limited extent of
advertising the host route.
-A do not ignore RIPv2 authentication if we do not care about RIPv2 authentication. This option
is required for conformance with RFC 1723. However, it makes no sense and breaks using RIP as
a discovery protocol to ignore all RIPv2 packets that carry authentication when this machine
does not care about authentication.
-T tracefile
increases the debugging level to at least 1 and causes debugging information to be appended to
the trace file. Note that because of security concerns, it is wisest to not run routed rou-tinely routinely
tinely with tracing directed to a file.
-t increases the debugging level, which causes more information to be logged on the tracefile
specified with -T or standard out. The debugging level can be increased or decreased with the
SIGUSR1 or SIGUSR2 signals.
-F net[/mask][,metric]
minimize routes in transmissions via interfaces with addresses that match net/mask, and synthe-sizes synthesizes
sizes a default route to this machine with the metric. The intent is to reduce RIP traffic on
slow, point-to-point links such as PPP links by replacing many large UDP packets of RIP infor-mation information
mation with a single, small packet containing a "fake" default route. If metric is absent, a
value of 14 is assumed to limit the spread of the "fake" default route. This is a dangerous
feature that when used carelessly can cause routing loops. Notice also that more than one
interface can match the specified network number and mask. See also -g.
-P parms
is equivalent to adding the parameter line parms to the /etc/gateways file.
Any other argument supplied is interpreted as the name of a file in which the actions of routed should
be logged. It is better to use -T instead of appending the name of the trace file to the command.
routed also supports the notion of "distant" passive or active gateways. When routed is started, it
reads the file /etc/gateways to find such distant gateways which may not be located using only informa-tion information
tion from a routing socket, to discover if some of the local gateways are passive, and to obtain other
parameters. 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 RIP packets.
Routes through passive gateways are installed in the kernel's routing tables once upon startup and are
not included in transmitted RIP responses.
Distant active gateways are treated like network interfaces. RIP responses are sent to the distant
active gateway. If no responses are received, the associated route is deleted from the kernel table
and RIP responses advertised via other interfaces. If the distant gateway resumes sending RIP
responses, the associated route is restored.
Such gateways can be useful on media that do not support broadcasts or multicasts but otherwise act
like classic shared media like Ethernets such as some ATM networks. One can list all RIP routers
reachable on the ATM network in /etc/gateways with a series of "host" lines.
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 indicate that another routing
process will install such a route if necessary, and that alternate routes to that destination should
not be installed by routed. Such entries are only required when both routers may learn of routes to
the same destination.
The /etc/gateways file is comprised of a series of lines, each in one of the following formats or con-sist consist
sist of parameters described below:
net Nname[/mask] gateway Gname metric value <passive | active | extern>
host Hname gateway Gname metric value <passive | active | extern>
Nname or Hname is the name of the destination network or host. It may be a symbolic network name or an
Internet address specified in "dot" notation (see inet(3) ). (If it is a name, then it must either be
defined in /etc/networks or /etc/hosts, or named(8), must have been started before routed.)
mask is an optional number between 1 and 32 indicating the netmask associated with Nname.
Gname is the name or address of the gateway to which RIP responses should be forwarded.
Value is the hop count to the destination host or network. host hname is equivalent to net
nname/32 .
One of the keywords passive, active or external must be present to indicate whether the gateway should
be treated as passive or active (as described above), or whether the gateway is external to the scope
of the RIP protocol.
Lines that start with neither "net" nor "host" must consist of one or more of the following parameter
settings, separated by commas or blanks:
if=ifname
indicates that the other parameters on the line apply to the interface name ifname.
subnet=nname[/mask][,metric]
advertises a route to network nname with mask mask and the supplied metric (default 1). This
is useful for filling "holes" in CIDR allocations. This parameter must appear by itself on a
line.
Do not use this feature unless necessary. It is dangerous.
passwd=XXX
specifies a RIPv2 password that will be included on all RIPv2 responses sent and checked on all
RIPv2 responses received. The password must not contain any blanks, tab characters, commas or
'#' characters.
no_ag turns off aggregation of subnets in RIPv1 and RIPv2 responses.
no_super_ag
turns off aggregation of networks into supernets in RIPv2 responses.
passive
is equivalent no_rip no_rdisc.
no_rip disables all RIP processing on the specified interface. If no interfaces are allowed to
process RIP packets, routed acts purely as a router discovery daemon. No_rip is equivalent to
no_ripv1_in no_ripv2_in no_ripv1_out no_ripv2_out.
Note that turning off RIP without explicitly turning on router discovery advertisements with
rdisc_adv or -s causes routed to act as a client router discovery daemon, not advertising.
no_ripv1_in
causes RIPv1 received responses to be ignored.
no_ripv2_in
causes RIPv2 received responses to be ignored.
ripv2_out
turns off RIPv1 output and causes RIPv2 advertisements to be multicast when possible.
no_rdisc
disables the Internet Router Discovery Protocol.
no_solicit
disables the transmission of Router Discovery Solicitations.
send_solicit
specifies that Router Discovery solicitations should be sent, even on point-to-point links,
which by default only listen to Router Discovery messages.
no_rdisc_adv
disables the transmission of Router Discovery Advertisements
rdisc_adv
specifies that Router Discovery advertisements should be sent, even on point-to-point links,
which by default only listen to Router Discovery messages
bcast_rdisc
specifies that Router Discovery packets should be broadcast instead of multicast.
rdisc_pref=N
sets the preference in Router Discovery Advertisements to the integer N.
rdisc_interval=N
sets the nominal interval with which Router Discovery Advertisements are transmitted to N sec-onds seconds
onds and their lifetime to 3*N.
fake_default=metric
has an identical effect to -F net[/mask][,metric] with the network and mask coming from the
specified interface.
pm_rdisc
is similar to fake_default. When RIPv2 routes are multicast, so that RIPv1 listeners cannot
receive them, this feature causes a RIPv1 default route to be broadcast to RIPv1 listeners.
Unless modified with fake_default, the default route is broadcast with a metric of 14. That
serves as a "poor man's router discovery" protocol.
Note that the netmask associated with point-to-point links (such as SLIP or PPP, with the IFF_POINTO-POINT IFF_POINTOPOINT
POINT flag) is used by routed to infer the netmask used by the remote system when RIPv1 is used.
FILES
/etc/gateways for distant gateways
SEE ALSO
udp(4), icmp(4).
Internet Transport Protocols, XSIS 028112, Xerox System Integration Standard.
BUGS
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.
4.4BSD June 1, 1996 4.4BSD
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