Routing Information Protocol (RIP): Latest Essentials and Grateful Guide


Routing Information Protocol or RIP is one of the oldest routing protocols. Bellman-Ford developed it in 1980. It passed through certain revisions which are version 1, version 2 for IPv4, and RIPng for IPv6. Moreover, it is a distance routing protocol that uses hop count as a metric. It is used in small as well as in medium-sized networks due to its simplicity and configuration. RIP v1 uses broadcasting to send its updates at regular intervals of time known as routing updates. This update consists of source and destination destination networks, IPs, and the number of hops required to reach the desired destination. It uses this information to make its routing table which enables it for forwarding decisions. However, RIPv2 and RIPng use multicast for its routing updates.

It uses hop count as a metric to reach to destination. All the routers that come in the RIP’s path are considered as hop count. The limitation of the hop count is 15. Hop count number 16 is considered unreachable. It is an IGP protocol.

It is developed for smaller networks because it requires fewer resources such as RAM and Processors. Routing Information protocol uses UDP port 520 for its updates. It is an open standard protocol.

 It sends its update to its neighbor periodically. Those updates are sent every 30 seconds. The updates include full updates instead of sending triggered or any change in routing information.


There are three versions which are version 1 and version 2 used by IPv4 while RIPng is used by IPv6.

  1. RIP v1     
  2. RIP v2                 
  3. RIP-ng

RIP v1 and V2

RIP v1 was developed in around 1980 while version 2 was standardized in 1998. Both versions support UDP port 520. RIP v1 uses broadcast while RIP v2 supports multicast for its routing updates. The objectives of both the version are the same.


RIPng stands for Routing Information Protocol Next Generation. It is an extension of RIP v2. However, It is designed, to support IPv6. It uses UDP port 521 for its routing updates. Similarly, It uses multicast address ff02::9, to share information with other RIP-ng-speaking routers.

Address FamilyIPv4IPv4IPv6
Subnet Mask SupportNoYesYes
Support VLSMNoYesYes
Multicast addressNo224.0.0.9FF02::9
Broadcast address255.255.255.255NoNo
Route TaggingNoYesYes
Automatic SummarizationYesNoNo
Convergence TimeSlowFasterFaster
IPv6 SupportNoNoYes
UDP Port Number520520521
Difference between RIP v1 V2 and RIPng


It uses four types of timers, which are below.

I) Update Timer

The update timer is 30 seconds. It sends its update to its neighbor after every 30 seconds.

II) Invalid Timer

It is 6 times of update timer. By default, the invalid timer is 180 seconds. It specifies the time for which it will wait, and after this time, Moreover, It will declare that specific router as invalid or it is now unreachable.

III) Flush Timer

It is a combination of an invalid timer plus 60 seconds more as 180+60=240 seconds. This is a time after which the unreachable route will be deleted from route entries e.g. routing table.

IV) Hold Down Timer

There is another fourth timer which is a hold-down timer which is 180 seconds. When a route is declared as unreachable then it will hold that entry up to 180 seconds. The purpose of this time is, that all routers should get an alert that this route has been down, and if there is any update about that down route, then it will not get that update.

Loop prevention mechanisms

When the start and end points meet at the same point, then it is called a loop. Routing loop means when the same packets circulate again and again in the network.

routing loops

The disadvantages of the loop are,

Our packets will never reach their destination

It is the wastage of  network bandwidth

It slows down network performance

There are some loop mechanisms which are below:

1) Route Poisoning

RIP-speaking router send full updates to its neighbor. It uses a 15 hops limit. It marks the 16th hop as infinity which indicates that it is unreachable.

If a network goes down for any reason, then router R1 will mark it with a special value, which is called count to infinity. It will send this update to its neighbor R2, that network attached with R1 is not reachable.

The update will reach R2 with a hop count of 16

R2 will also send this update to its neighbor R3.

So that update will be sent to R3. In this way, all the routes have received this information.

2) Split Horizon

Split horizon is another method that is used in loop prevention mechanisms. It Is a method in which network information is not sent back on the same interface through which it received that information a few seconds ago.

We are going to take back the previous diagram. The network attached to R1 has been down, so R1 will send this update to R2 with a hop count of 16 and it is now unreachable.

RIP split horizon IMG1

R2 will receive this update with a hop count of 16.

RIP split horizon IMG2

When it reaches R2, then R2 will send this update to its neighbor. There are two neighbors of R2, which are R1 and R3. So R2 will send it to R1 and R3.

RIP split horizon IMG3

R1 has sent this update to R2, But R2 is sending this update back to R1. R1 will send it to R2, and R2 will send it back to R1, which will create a loop in the network. As we don’t want to loop in the network, because it will slow down our network.

RIP split horizon IMG3

So, the role of split horizon is that an update received on any interface will not be sent back on the same interface. And, so R2 will send it only to the R3, but not back to R1 on the same link.

RIP split horizon IMG4

3) Poison Reverse

The poison role specifies that when a router receives any failed route information, it immediately sends this update to the inter-network.

4) Hold-down timer

There is also another mechanism in routing information protocol for loop prevention, which is called a hold-down timer. As any route or network segment becomes down in the RIP inter-network, then it is considered poison reverse. A RIP start timer is called a hold-down timer. If a route is poisoned or down, a router will retain its associated information for a specific duration. As long as this timer runs, no router in the inter-network will update its routing table about that specific failed route coming from any router. The purpose of this timer is that all routers will know in that specific way which route has been down.

5) RIP trigger update

By default, RIُ sends its update periodically. It updates its neighbor every 30 seconds. But in a triggered update, as the route becomes down, the router doesn’t wait for the next update, but it sends its update immediately to its neighbor. The advantage of it is that the failed route updates immediately expand the inter-network.

Configuration of RIP v1 and v2 Lab topology

Routing information protocol lab topology

Configure version 1 on R1 and R2, while version 2 on R3.

Routing information protocol configuration

Run the commands #show ip route and #show ip protocol on R1 to watch routing behavior.

The routers learned through RIP is represented by the letter “D” after running the show IP route command. While we also ran the command “show IP Protocol”,

Similarly, run the above commands on R4.

Ping from R1 to R3 to test connectivity.

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