RIP

RIP – Routing Information Protocol is widely deployed interior gateway protocol. RIP was developed in the 1970s at Xerox Labs as part of the XNS routing protocol. RIP is a distance-vector protocol and is based on the Bellman-Ford algorithms. As a distance-vector protocol, RIP router send updates to its neighbors periodically, thus allowing the convergence to a known topology. In each update, the distance to any given network will be broadcast to its neighboring router.

ripd supports RIP version 2 as described in RFC2453 and RIP version 1 as described in RFC1058.

Starting and Stopping ripd

The default configuration file name of ripd’s is ripd.conf. When invocation ripd searches directory /etc/frr. If ripd.conf is not there next search current directory.

RIP uses UDP port 520 to send and receive RIP packets. So the user must have the capability to bind the port, generally this means that the user must have superuser privileges. RIP protocol requires interface information maintained by zebra daemon. So running zebra is mandatory to run ripd. Thus minimum sequence for running RIP is like below:

# zebra -d
# ripd -d

Please note that zebra must be invoked before ripd.

To stop ripd. Please use::
kill cat /var/run/ripd.pid

Certain signals have special meanings to ripd.

Signal Action
SIGHUP Reload configuration file ripd.conf. All configurations are reset. All routes learned so far are cleared and removed from routing table.
SIGUSR1 Rotate the ripd logfile.
SIGINT SIGTERM Sweep all installed routes and gracefully terminate.

ripd invocation options. Common options that can be specified (Common Invocation Options).

RIP netmask

The netmask features of ripd support both version 1 and version 2 of RIP. Version 1 of RIP originally contained no netmask information. In RIP version 1, network classes were originally used to determine the size of the netmask. Class A networks use 8 bits of mask, Class B networks use 16 bits of masks, while Class C networks use 24 bits of mask. Today, the most widely used method of a network mask is assigned to the packet on the basis of the interface that received the packet. Version 2 of RIP supports a variable length subnet mask (VLSM). By extending the subnet mask, the mask can be divided and reused. Each subnet can be used for different purposes such as large to middle size LANs and WAN links. FRR ripd does not support the non-sequential netmasks that are included in RIP Version 2.

In a case of similar information with the same prefix and metric, the old information will be suppressed. Ripd does not currently support equal cost multipath routing.

RIP Configuration

router rip

The router rip command is necessary to enable RIP. To disable RIP, use the no router rip command. RIP must be enabled before carrying out any of the RIP commands.

Disable RIP.

network NETWORK

Set the RIP enable interface by NETWORK. The interfaces which have addresses matching with NETWORK are enabled.

This group of commands either enables or disables RIP interfaces between certain numbers of a specified network address. For example, if the network for 10.0.0.0/24 is RIP enabled, this would result in all the addresses from 10.0.0.0 to 10.0.0.255 being enabled for RIP. The no network command will disable RIP for the specified network.

network IFNAME

Set a RIP enabled interface by IFNAME. Both the sending and receiving of RIP packets will be enabled on the port specified in the network ifname command. The no network ifname command will disable RIP on the specified interface.

neighbor A.B.C.D

Specify RIP neighbor. When a neighbor doesn’t understand multicast, this command is used to specify neighbors. In some cases, not all routers will be able to understand multicasting, where packets are sent to a network or a group of addresses. In a situation where a neighbor cannot process multicast packets, it is necessary to establish a direct link between routers. The neighbor command allows the network administrator to specify a router as a RIP neighbor. The no neighbor a.b.c.d command will disable the RIP neighbor.

Below is very simple RIP configuration. Interface eth0 and interface which address match to 10.0.0.0/8 are RIP enabled.

!
router rip
 network 10.0.0.0/8
 network eth0
!
passive-interface (IFNAME|default)

This command sets the specified interface to passive mode. On passive mode interface, all receiving packets are processed as normal and ripd does not send either multicast or unicast RIP packets except to RIP neighbors specified with neighbor command. The interface may be specified as default to make ripd default to passive on all interfaces.

The default is to be passive on all interfaces.

ip split-horizon

Control split-horizon on the interface. Default is ip split-horizon. If you don’t perform split-horizon on the interface, please specify no ip split-horizon.

RIP Version Control

RIP can be configured to send either Version 1 or Version 2 packets. The default is to send RIPv2 while accepting both RIPv1 and RIPv2 (and replying with packets of the appropriate version for REQUESTS / triggered updates). The version to receive and send can be specified globally, and further overridden on a per-interface basis if needs be for send and receive separately (see below).

It is important to note that RIPv1 cannot be authenticated. Further, if RIPv1 is enabled then RIP will reply to REQUEST packets, sending the state of its RIP routing table to any remote routers that ask on demand. For a more detailed discussion on the security implications of RIPv1 see RIP Authentication.

version VERSION

Set RIP version to accept for reads and send. VERSION can be either 1 or 1.

Disabling RIPv1 by specifying version 2 is STRONGLY encouraged, RIP Authentication. This may become the default in a future release.

Default: Send Version 2, and accept either version.

ip rip send version VERSION

VERSION can be 1, 2, or 1 2.

This interface command overrides the global rip version setting, and selects which version of RIP to send packets with, for this interface specifically. Choice of RIP Version 1, RIP Version 2, or both versions. In the latter case, where 1 2 is specified, packets will be both broadcast and multicast.

Default: Send packets according to the global version (version 2)

ip rip receive version VERSION

VERSION can be 1, 2, or 1 2.

This interface command overrides the global rip version setting, and selects which versions of RIP packets will be accepted on this interface. Choice of RIP Version 1, RIP Version 2, or both.

Default: Accept packets according to the global setting (both 1 and 2).

How to Announce RIP route

redistribute <babel|bgp|connected|eigrp|isis|kernel|openfabric|ospf|sharp|static|table> [metric (0-16)] [route-map WORD]

Redistribute routes from other sources into RIP.

If you want to specify RIP only static routes:

default-information originate
route A.B.C.D/M

This command is specific to FRR. The route command makes a static route only inside RIP. This command should be used only by advanced users who are particularly knowledgeable about the RIP protocol. In most cases, we recommend creating a static route in FRR and redistributing it in RIP using redistribute static.

Filtering RIP Routes

RIP routes can be filtered by a distribute-list.

distribute-list ACCESS_LIST DIRECT IFNAME

You can apply access lists to the interface with a distribute-list command. ACCESS_LIST is the access list name. DIRECT is in or out. If DIRECT is in the access list is applied to input packets.

The distribute-list command can be used to filter the RIP path. distribute-list can apply access-lists to a chosen interface. First, one should specify the access-list. Next, the name of the access-list is used in the distribute-list command. For example, in the following configuration eth0 will permit only the paths that match the route 10.0.0.0/8

!
router rip
 distribute-list private in eth0
!
access-list private permit 10 10.0.0.0/8
access-list private deny any
!

distribute-list can be applied to both incoming and outgoing data.

distribute-list prefix PREFIX_LIST (in|out) IFNAME

You can apply prefix lists to the interface with a distribute-list command. PREFIX_LIST is the prefix list name. Next is the direction of in or out. If DIRECT is in the access list is applied to input packets.

RIP Metric Manipulation

RIP metric is a value for distance for the network. Usually ripd increment the metric when the network information is received. Redistributed routes’ metric is set to 1.

default-metric (1-16)

This command modifies the default metric value for redistributed routes. The default value is 1. This command does not affect connected route even if it is redistributed by redistribute connected. To modify connected route’s metric value, please use redistribute connected metric or route-map. offset-list also affects connected routes.

offset-list ACCESS-LIST (in|out)
offset-list ACCESS-LIST (in|out) IFNAME

RIP distance

Distance value is used in zebra daemon. Default RIP distance is 120.

distance (1-255)

Set default RIP distance to specified value.

distance (1-255) A.B.C.D/M

Set default RIP distance to specified value when the route’s source IP address matches the specified prefix.

distance (1-255) A.B.C.D/M ACCESS-LIST

Set default RIP distance to specified value when the route’s source IP address matches the specified prefix and the specified access-list.

RIP route-map

Usage of ripd’s route-map support.

Optional argument route-map MAP_NAME can be added to each redistribute statement.

redistribute static [route-map MAP_NAME]
redistribute connected [route-map MAP_NAME]
.....

Cisco applies route-map _before_ routes will exported to rip route table. In current FRR’s test implementation, ripd applies route-map after routes are listed in the route table and before routes will be announced to an interface (something like output filter). I think it is not so clear, but it is draft and it may be changed at future.

Route-map statement (Route Maps) is needed to use route-map functionality.

match interface WORD

This command match to incoming interface. Notation of this match is different from Cisco. Cisco uses a list of interfaces - NAME1 NAME2 … NAMEN. Ripd allows only one name (maybe will change in the future). Next - Cisco means interface which includes next-hop of routes (it is somewhat similar to “ip next-hop” statement). Ripd means interface where this route will be sent. This difference is because “next-hop” of same routes which sends to different interfaces must be different. Maybe it’d be better to made new matches - say “match interface-out NAME” or something like that.

match ip address WORD
match ip address prefix-list WORD

Match if route destination is permitted by access-list.

match ip next-hop WORD
match ip next-hop prefix-list WORD

Match if route next-hop (meaning next-hop listed in the rip route-table as displayed by “show ip rip”) is permitted by access-list.

match metric (0-4294967295)

This command match to the metric value of RIP updates. For other protocol compatibility metric range is shown as (0-4294967295). But for RIP protocol only the value range (0-16) make sense.

set ip next-hop A.B.C.D

This command set next hop value in RIPv2 protocol. This command does not affect RIPv1 because there is no next hop field in the packet.

set metric (0-4294967295)

Set a metric for matched route when sending announcement. The metric value range is very large for compatibility with other protocols. For RIP, valid metric values are from 1 to 16.

RIP Authentication

RIPv2 allows packets to be authenticated via either an insecure plain text password, included with the packet, or via a more secure MD5 based HMAC, RIPv1 can not be authenticated at all, thus when authentication is configured ripd will discard routing updates received via RIPv1 packets.

However, unless RIPv1 reception is disabled entirely, RIP Version Control, RIPv1 REQUEST packets which are received, which query the router for routing information, will still be honoured by ripd, and ripd WILL reply to such packets. This allows ripd to honour such REQUESTs (which sometimes is used by old equipment and very simple devices to bootstrap their default route), while still providing security for route updates which are received.

In short: Enabling authentication prevents routes being updated by unauthenticated remote routers, but still can allow routes (I.e. the entire RIP routing table) to be queried remotely, potentially by anyone on the internet, via RIPv1.

To prevent such unauthenticated querying of routes disable RIPv1, RIP Version Control.

ip rip authentication mode md5

Set the interface with RIPv2 MD5 authentication.

ip rip authentication mode text

Set the interface with RIPv2 simple password authentication.

ip rip authentication string STRING

RIP version 2 has simple text authentication. This command sets authentication string. The string must be shorter than 16 characters.

ip rip authentication key-chain KEY-CHAIN

Specify Keyed MD5 chain.

!
key chain test
 key 1
  key-string test
!
interface eth1
 ip rip authentication mode md5
 ip rip authentication key-chain test
!

RIP Timers

timers basic UPDATE TIMEOUT GARBAGE

RIP protocol has several timers. User can configure those timers’ values by timers basic command.

The default settings for the timers are as follows:

  • The update timer is 30 seconds. Every update timer seconds, the RIP process is awakened to send an unsolicited Response message containing the complete routing table to all neighboring RIP routers.
  • The timeout timer is 180 seconds. Upon expiration of the timeout, the route is no longer valid; however, it is retained in the routing table for a short time so that neighbors can be notified that the route has been dropped.
  • The garbage collect timer is 120 seconds. Upon expiration of the garbage-collection timer, the route is finally removed from the routing table.

The timers basic command allows the the default values of the timers listed above to be changed.

Show RIP Information

To display RIP routes.

show ip rip

Show RIP routes.

The command displays all RIP routes. For routes that are received through RIP, this command will display the time the packet was sent and the tag information. This command will also display this information for routes redistributed into RIP.

show ip rip status

The command displays current RIP status. It includes RIP timer, filtering, version, RIP enabled interface and RIP peer information.

ripd> **show ip rip status**
Routing Protocol is "rip"
  Sending updates every 30 seconds with +/-50%, next due in 35 seconds
  Timeout after 180 seconds, garbage collect after 120 seconds
  Outgoing update filter list for all interface is not set
  Incoming update filter list for all interface is not set
  Default redistribution metric is 1
  Redistributing: kernel connected
  Default version control: send version 2, receive version 2
    Interface  Send  Recv
  Routing for Networks:
    eth0
    eth1
    1.1.1.1
    203.181.89.241
  Routing Information Sources:
    Gateway    BadPackets BadRoutes  Distance Last Update

RIP Debug Commands

Debug for RIP protocol.

debug rip events

Shows RIP events. Sending and receiving packets, timers, and changes in interfaces are events shown with ripd.

debug rip packet

Shows display detailed information about the RIP packets. The origin and port number of the packet as well as a packet dump is shown.

debug rip zebra

This command will show the communication between ripd and zebra. The main information will include addition and deletion of paths to the kernel and the sending and receiving of interface information.

show debugging rip

Shows all information currently set for ripd debug.