ROUTED(8) BSD System Manager's Manual ROUTED(8)NAMErouted - network RIP and router discovery routing daemon
SYNOPSISrouted [-Adghmqst] [-F net[/mask][,metric]] [-P parms] [-T tracefile]
DESCRIPTIONrouted is a daemon invoked at boot time to manage the network routing
tables. It uses Routing Information Protocol Version 1 (RFC 1058), RIPv2
(RFC 1723), and Internet Router Discovery Protocol (RFC 1256) to maintain
the kernel routing table.
It listens on a udp(4) socket for the route(8) service (see services(5))
for Routing Information Protocol packets. It also sends and receives mul-
ticast Router Discovery ICMP messages. If the host is a router, routed
periodically supplies copies of its routing tables to any directly con-
nected hosts and networks. It also advertises 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 the kernel table, except those marked with either the RTF_PROTO1 or
RTF_PROTO2 flag (see route(4)), i.e. routes that have been inserted by
bgpd(8) or ospfd(8). 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 inter-
face), it is assumed that the host should forward packets among the con-
nected 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 gen-
erated 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 an interface (see
ifconfig(8)), so setting the metric on an interface is an effective way
to steer traffic.
Responses do not contain routes with a first hop on the requesting net-
work to implement in part split-horizon. Requests from query programs
such as rtquery(8) are answered with the complete table.
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 pro-
vided 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 infin-
ite metric to ensure 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 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 sup-
port 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(1)), then the cable or some other part of the interface is
assumed to be disconnected or broken, and routes are adjusted appropri-
ately.
The Internet Router Discovery Protocol is handled similarly. When the
daemon is supplying RIP routes, it also listens for Router Discovery Sol-
icitations and sends Advertisements. When it is quiet and only listening
to other RIP routers, it sends Solicitations and listens for Advertise-
ments. If it receives a good Advertisement, it stops listening for broad-
cast 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 re-
ceived), 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).
The options are as follows:
-A Drop all RIPv2 packets carrying authentication information. This
option is required for conformance with RFC 1723, even though it
breaks RIP as a discovery protocol.
-d Do not run in the background. This option is meant for interac-
tive use.
-F net[/mask][,metric]
Minimize routes in transmissions via interfaces with addresses
that match net/mask, and synthesizes 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 information 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.
-g 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 potential-
ly dangerous default route. This is typically used on a gateway
to the Internet, or on a gateway that uses another routing proto-
col 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 accidentally used to create chaos with a routing
loop than to solve problems.
-h Causes host or point-to-point routes to not be advertised, pro-
vided 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 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 popular-
ity of the server. It is effective only when the machine is sup-
plying routing information, because there is more than one inter-
face. The -m option overrides the -q option to the limited extent
of advertising the host route.
-P parms
Equivalent to adding the parameter line parms to the
/etc/gateways file.
-q Opposite of the -s option.
-s Forces routed to supply routing information. This is the default
if multiple network interfaces are present on which RIP or Router
Discovery have not been disabled, and if the kernel sysctl(8)
net.inet.ip.forwarding=1.
-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 routinely
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 or with the rtquery(8) command.
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 dis-
tant gateways which may not be located using only information 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 informa-
tion, 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 re-
ceived, 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 ker-
nel routing table nor are they included in routing updates. The function
of external entries is to indicate that another routing process will in-
stall such a route if necessary, and that alternate routes to that desti-
nation 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 consist 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" nota-
tion (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 asso-
ciated 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 indi-
cate 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 in-
terface name ifname. This typically is the first entry in all
lines in /etc/gateways.
subnet=nname[/mask][,metric]
Advertises a route to network nname with mask mask and the sup-
plied 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
Equivalent to no_rip no_rdisc.
no_rip Disables all RIP processing on the specified interface (no RIP
will be transmitted, and any received RIP packets will be ig-
nored). If no interfaces are allowed to process RIP packets,
routed acts purely as a router discovery daemon. Note that turn-
ing off RIP without explicitly turning on router discovery adver-
tisements 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 mul-
ticast 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 in-
stead of multicast.
rdisc_pref=N
Sets the preference in Router Discovery Advertisements to the in-
teger N.
rdisc_interval=N
Sets the nominal interval with which Router Discovery Advertise-
ments are transmitted to N seconds and their lifetime to 3*N.
fake_default=metric
Has an identical effect to -F net[/mask][,metric] with the net-
work and mask coming from the specified interface.
pm_rdisc
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_POINTOPOINT 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 ALSOnetstat(1), icmp(4), route(4), udp(4), bgpd(8), ifconfig(8), ospfd(8),
route(8), rtquery(8)
Internet Transport Protocols, XSIS 028112, Xerox System Integration
Standard.
HISTORY
The routed command appeared in 4.2BSD.
BUGS
It does not always detect unidirectional failures in network interfaces
(e.g. when the output side fails).
MirOS BSD #10-current June 1, 1996 5
