Routing Information Protocol - RIP

Routing Information Protocol - RIP  is an Interior Gateway Protocol that is designed to support routing in small private networks. It is an Application layer protocol that runs on top of UDP well-known port 520.

Routing Information Protocol Versions

Routing Information Protocol operates using two versions:  RIP Version1 and RIP Version2

Routing Information Protocol Protocol Type

Distance Vector. The term 'Distance' means how many hops away the destination subnet is located and 'Vector' is technical name for direction, means, through which next-hop or exit interface the destination prefix is located.

Routing Information Protocol Default AD

RIP has default AD value of 120 (for both version 1 and version 2). Can be changed using "distance x" router configuration command.

Routing Information Protocol Mertic

RIP considers Hop Count as its metric. Maximum Hop count allowed is 15. A destination that is 16 hops away is considered unreachable. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from source to destination.

Routing Information Protocol Algorithm

RIP uses Bellman-Ford algorithm to compute the metric.

Routing Information Protocol Timers

RIP does not have any way of reliability therefore the updates are sent periodically every 30 seconds. RIPv1 Broadcast address are used at both Layer 2 (FF:FF:FF:FF:FF:FF) and Layer 3 (255.255.255.255).  RIPv2 uses Multicast addresses at both Layer 2 (01:00:5e:00:00:09) and Layer 3(224.0.0.9).  Below is brief description of RIP timers. Kindly read the article RIP Timers for more details.

• Update: The time between each update interval. This value is set to 30 seconds, by default, and is configurable.
• Invalid:  The time after which a suspect route becomes invalid. This is set to 180 seconds, by default.
• Hold-down: The time used to suppress the possibility of defective routes being installed in the routing table. The default time is 180 seconds.
• Flush: The time after which a route is removed from the routing table. This is set to 240 seconds, by default.

Routing Information Protocol Authentication

RIPv1 does not support Authentication. Only RIPv2 supports Authentication.

A router can be configured to run RIPv1 as well as RIPv2 at same time. In a topology R1--R2--R3, R2 is running RIPv2, however, it can also be configured to run RIPv1 with R1(if R1 doesn't support v2 due to IOS constraints) and R2 can run RIPv2 with R3.  Below is interface level command where R2 is configured to run Version1 with R1 (R2's f1/0 is interface connected to R1).

R2(config-router)#int f1/0
R2(config-if)#ip rip send version 1

Routing Information Protocol Commands

R1#show ip protocols
Routing Protocol is "rip"
  Outgoing update filter list for all interfaces is not set
  Incoming update filter list for all interfaces is not set
  Sending updates every 30 seconds, next due in 27 seconds
  Invalid after 180 seconds, hold down 180, flushed after 240
  Redistributing: rip
  Default version control: send version 2, receive version 2
    Interface                Send  Recv  Triggered RIP  Key-chain
    FastEthernet1/0       1     2
    FastEthernet1/1        2     2
    Loopback0                2     2
  Automatic network summarization is not in effect
  Maximum path: 4
  Routing for Networks:
    10.0.0.0
  Routing Information Sources:
    Gateway         Distance      Last Update
    10.10.12.1           120      00:02:38
    10.10.23.3           120      00:00:09
  Distance: (default is 120)

RIP stores all the updates received its peers first in the database (control plane). The best routes from the database are moved to the routing table.

R2#show ip rip database
10.0.0.0/8    auto-summary
10.10.0.0/24    directly connected, Loopback0
10.10.0.1/32
    [1] via 10.10.12.1, 00:00:19, FastEthernet1/0
10.10.12.0/24    directly connected, FastEthernet1/0
10.10.23.0/24    directly connected, FastEthernet1/1

 

R2#Show ip route rip
Gateway of last resort is not set
          10.0.0.0/8 is variably subnetted, 8 subnets, 2 masks
R        10.10.25.0/24 [120/1] via 10.10.12.2, 00:00:05, FastEthernet1/0
R        10.10.35.0/24 [120/2] via 10.10.14.4, 00:00:06, FastEthernet2/0
           192.9.1.0/32 is subnetted, 1 subnets
R        192.9.1.5 [120/2] via 10.10.14.4, 00:00:06, FastEthernet2/0

RIP routes are denoted by 'R' in the Routing table.

We can also use RIP debugging for troubleshooting routing issues related to RIP.

 

R1#debug ip rip
RIP protocol debugging is on
R1#
*Sep  3 20:31:09.755: RIP: sending v2 update to 224.0.0.9 via FastEthernet2/0 (10.10.14.1)
*Sep  3 20:31:09.759: RIP: build update entries
*Sep  3 20:31:09.763:   10.10.12.0/24 via 0.0.0.0, metric 1, tag 0
*Sep  3 20:31:09.767:   10.10.13.0/24 via 0.0.0.0, metric 1, tag 0
*Sep  3 20:31:09.767:   10.10.25.0/24 via 0.0.0.0, metric 2, tag 0
R1#

Click Here for other useful RIP articles

 

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