network RIP and router discovery routing daemon
utility is a daemon invoked at
boot time to manage the network routing tables. It uses Routing Information
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
It listens on the
socket for the
for Routing Information Protocol packets. It also sends and receives multicast
Router Discovery ICMP messages. If the host is a router,
periodically supplies copies of its
routing tables to any directly connected 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),
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,
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 -hopcount (see
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
Discovery Advertisements or Solicitations on a new interface, the daemon
enters a loop, listening for RIP request and response and Router Discovery
packets from other hosts.
When a request
packet is received,
formulates a reply based on the
information maintained in its internal tables. The
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 advertised metric for a
route reflects the metrics associated with interfaces (see
though which it is received and sent, so setting the metric on an interface is
an effective way to steer traffic. See also
Responses do not include routes with a first hop on the requesting network to
implement in part split-horizon
. Requests from
query programs such as
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
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
When an update is applied,
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
sent. If the next response is not scheduled for a while, a
response containing only recently
changed routes is sent.
In addition to processing incoming packets,
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 ensure the
invalidation is propagated throughout the local internet. This is a form of
Routes in the kernel table that are added or changed as a result of ICMP
Redirect messages are deleted after a while to minimize
. When a TCP connection suffers a
timeout, the kernel tells
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
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
similarly. When the daemon is supplying RIP routes, it also listens for Router
Discovery Solicitations and sends Advertisements. When it is quiet and
listening to other RIP routers, it sends Solicitations and listens for
Advertisements. If it receives a good Advertisement and it is not multi-homed,
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. It continues listening to RIP while using Router Discovery if
multi-homed to ensure all interfaces are used.
The Router Discovery 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
on the command line or
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. On a host with more than one network interface,
this default route will be via only one of the interfaces. Thus, multi-homed
hosts running with
facility described below to
support "legacy" systems that can handle neither RIPv2 nor Router
By default, neither Router Discovery advertisements nor solicitations are sent
over point to point links (e.g. PPP). The netmask associated with
point-to-point links (such as SLIP or PPP, with the IFF_POINTOPOINT flag) is
to infer the netmask used by
the remote system when RIPv1 is used.
The following options are available:
routed to accept a RIP request
from non-router node. When specified once,
routed replies to a route information
query from neighbor nodes. When specified twice, it replies to a query
from remote nodes in addition.
utility can be used to send a request.
This feature is disabled by default because of a risk of reflection attack
though it is useful for debugging purpose.
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 switch ipforwarding=1.
- is the opposite of the
-s option. This
is the default when only one interface is present. With this explicit
option, the daemon is always in "quiet-mode" for RIP and does
not supply routing information to other computers.
- do not run in the background. This option is meant for interactive
- used on internetwork routers to offer a route to the "default"
destination. It is equivalent to
0/0,1 and is present mostly for
historical reasons. A better choice is
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 accidentally used to create
chaos with a routing loop than to solve problems.
- cause 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
- cause 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.
- 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.
- increase the debugging level, which causes more information to be logged
on the tracefile specified with
standard out. The debugging level can be increased or decreased with the
SIGUSR2 signals or with the
- 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.
- display and logs the version of daemon.
- 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
- is equivalent to adding the parameter line
parms to the
Any other argument supplied is interpreted as the name of a file in which the
should be logged. It is
better to use
instead of appending the
name of the trace file to the command.
utility also supports the notion
of "distant" passive
is started, it reads the file
to find such distant gateways
which may not be located using only information from a routing socket, to
discover if some of the local gateways are
, 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 HIPPI or ATM
network in /etc/gateways
with a series of
"host" lines. Note that it is usually desirable to use RIPv2 in such
situations to avoid generating lists of inferred host routes.
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 other routes to that
destination should not be installed by
. Such entries are only required when
both routers may learn of routes to the same destination.
file is comprised of a
series of lines, each in one of the following two formats or consist of
parameters described later. Blank lines and lines starting with '#' are
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
(If it is a name, then it must either be defined in
must have been started before
is an optional number between 1 and 32
indicating the netmask associated with Nname
is the name or address of the gateway to
which RIP responses should be forwarded.
is the hop count to the destination host
is equivalent to
One of the keywords
must be present to indicate
whether the gateway should be treated as
(as described above), or whether the
to the scope of the RIP
As can be seen when debugging is turned on with
, such lines create pseudo-interfaces. To
set parameters for remote or external interfaces, a line starting with
, etc. should be used.
Lines that start with neither "net" nor "host" must consist
of one or more of the following parameter settings, separated by commas or
- indicates that the other parameters on the line apply to the interface
- 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. The network
number must specify a full, 32-bit value, as in 192.0.2.0 instead of
Do not use this feature unless necessary. It is dangerous.
- specifies that netmask of the network of which
is a subnet should be mask2. For example,
192.0.2.16/28 as a subnet of 192.0.2.0/27 instead of 192.0.2.0/24. It is
better to turn on RIPv2 instead of using this facility, for example with
- specifies a RIPv2 cleartext password that will be included on all RIPv2
responses sent, and checked on all RIPv2 responses received. Any blanks,
tab characters, commas, or '#', '|', or NULL characters in the password
must be escaped with a backslash (\). The common escape sequences \n, \r,
\t, \b, and \xxx have their usual meanings. The
KeyID must be unique but is ignored for
cleartext passwords. If present,
stop are timestamps in the form
year/month/day@hour:minute. They specify when the password is valid. The
valid password with the most future is used on output packets, unless all
passwords have expired, in which case the password that expired most
recently is used, or unless no passwords are valid yet, in which case no
password is output. Incoming packets can carry any password that is valid,
will be valid within the next 24 hours, or that was valid within the
preceding 24 hours. To protect the secrets, the passwd settings are valid
only in the /etc/gateways file and only
when that file is readable only by UID 0.
- specifies a RIPv2 MD5 password. Except that a
KeyID is required, this keyword is
- turns off aggregation of subnets in RIPv1 and RIPv2 responses.
- turns off aggregation of networks into supernets in RIPv2 responses.
- marks the interface to not be advertised in updates sent via other
interfaces, and turns off all RIP and router discovery through the
- disables all RIP processing on the specified interface. If no interfaces
are allowed to process RIP packets,
routed acts purely as a router
Note that turning off RIP without explicitly turning on router discovery
routed to act as a client router
discovery daemon, not advertising.
- causes RIPv2 packets to be broadcast instead of multicast.
- causes no RIP updates to be sent.
- causes RIPv1 received responses to be ignored.
- causes RIPv2 received responses to be ignored.
- turns on RIPv2 output and causes RIPv2 advertisements to be multicast when
- is equivalent to
no_ripv1_out. This enables RIPv2.
- disables the Internet Router Discovery Protocol.
- disables the transmission of Router Discovery Solicitations.
- specifies that Router Discovery solicitations should be sent, even on
point-to-point links, which by default only listen to Router Discovery
- disables the transmission of Router Discovery Advertisements.
- specifies that Router Discovery Advertisements should be sent, even on
point-to-point links, which by default only listen to Router Discovery
- specifies that Router Discovery packets should be broadcast instead of
- sets the preference in Router Discovery Advertisements to the optionally
signed integer N. The default preference
is 0. Default routes with smaller or more negative preferences are
preferred by clients.
- sets the nominal interval with which Router Discovery Advertisements are
transmitted to N seconds and their lifetime to 3*N.
- has an identical effect to
net[/mask][=metric] with the network and
mask coming from the specified interface.
- 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
default route is broadcast with a metric of 14. That serves as a
"poor man's router discovery" protocol.
- adjusts the hop count or metric of received RIP routes by
delta. The metric of every received RIP
route is increased by the sum of two values associated with the interface.
One is the adj_inmetric value and the other is the interface metric set
- adjusts the hop count or metric of advertised RIP routes by
delta. The metric of every received RIP
route is increased by the metric associated with the interface by which it
was received, or by 1 if the interface does not have a non-zero metric.
The metric of the received route is then increased by the adj_outmetric
associated with the interface. Every advertised route is increased by a
total of four values, the metric set for the interface by which it was
delta of the receiving interface, the
metric set for the interface by which it is transmitted with
delta of the transmitting interface.
- causes RIP packets from router rname and
other routers named in other
trust_gateway keywords to be accepted,
and packets from other routers to be ignored. If networks are specified,
then routes to other networks will be ignored from that router.
- allows the kernel to listen ICMP Redirect messages when the system is
acting as a router and forwarding packets. Otherwise, ICMP Redirect
messages are overridden and deleted when the system is acting as a
- for distant gateways
Protocols, XSIS 028112,
Xerox System Integration Standard.
utility appeared in
It does not always detect unidirectional failures in network interfaces, for
example, when the output side fails.