This tutorial explains the differences between the RIPv1 and RIPv2 routing protocols. Learn what RIP timers are and how they are used by the RIP protocol to perform its basic operations.
There are two different versions of the RIP routing protocol: RIPv1 and RIPv2. RIPv1 is one of the first most popular IP routing protocols. It was widely used until the 90s. RIPv1 is no longer used in modern networks.
RIPv2 was developed in the 90s as an enhancement of the RIPv1. To make RIP more suitable for modern networks, in RIPv2 not only many functions of RIPv1 were improved but many new features were also added.
To understand which functions were improved and which features were newly added, in the following section, we will compare RIPv1 and RIPv2 routing protocols.
How RIP Routing Protocol Works
This is the first part of the article. This part explains how the RIP routing protocol uses broadcast messages to exchange network paths' information.
RIP Routing Information Protocol Explained
This is the second part of the article. This part explains the concept of distance-vector routing and how the RIP routing protocol uses this concept.
Comparing RIPv1 and RIPv2 routing protocols
RIPv1 is a true distance-vector routing protocol. Although RIPv2 is based on RIPv1 and at heart it is also a distance-vector routing protocol, still, due to some added features, RIPv2 is sometimes considered as a hybrid routing protocol.
To find and select a single best route for each IP subnet of the network, both versions use the hops-count metric. The maximum hops count limit is set to 15 on both versions.
RIPv1 uses broadcast messages to advertise routing updates. To advertise routing updates, RIPv2 uses a multicast address 224.0.0.9. This enhancement saves a lot of bandwidths of the network.
RIPv1 does not support trigger updates. RIPv2 supports trigger updates. It means, when a change occurs, RIPv2 will immediately propagate this information to its connected neighbors while RIPv1 will broadcast this information to its neighbors only in the next scheduled broadcast message. Trigger updates speed up the convergence process.
RIPv1 is a classful routing protocol while RIPv2 is a classless routing protocol. A classful routing protocol does not support variable-length subnet masking (VLSM). VLSM is a routing feature that allows us to use more than one subnet mask for a given class network number. VLSM maximizes the efficiency of IP addressing design as well as summarize routing information to create very large, scalable networks.
RIPv1 does not support any type of authentication while RIPv2 supports MD5 authentication. In RIPv2, we can restrict what routers we want to participate in.
RIPv1 and RIPv2 both use the split horizon, route poisoning, and various timers to perform their basic operations. In the following section, we will understand RIP timers while we will understand the split horizon and route poisoning in the next parts of this tutorial.
RIP timers
RIP uses four different types of timers. These timers are: update timer, route invalid timer, route flash timer, and hold-down timer.
The following images show an example of these timers.
Let's understand each timer in detail
Update timer: -
RIP uses this timer to set the interval between two continuous routing updates. The default value of this timer is 30 seconds. After advertising a routing update, RIP waits 30 seconds before advertising the next routing update.
Route invalid timer: -
RIP learns new routes from the received routing update. After learning new routes, when RIP adds them to the routing table, it also adds an invalid timer with each route. RIP uses this timer to get rid of routes that become invalid in the future.
In upcoming routing updates, if RIP receives the same information on a route, it resets the invalid timer of that route in the routing table. If RIP does not receive the same information on a route in 180 seconds, it assumes that the route is no longer available. When this happens, RIP sends an update to all its neighbors to indicate that the route is invalid.
Route flush timer: -
RIP uses this timer to flush invalid routes from the routing table. The value of this timer must be set higher than the value of the invalid timer. This gives the RIP enough time to tell its neighbors about an invalid route before the invalid route is removed from the routing table. The default value of this timer is 240 seconds.
Hold-down timer: -
RIP uses this timer to quickly identify invalid routes. When RIP receives a routing update that contains information about an invalid route, the RIP immediately starts the hold-down timer for that route in the routing table. The default value of the hold timer is 180 seconds.
RIP stops and removes this timer from an invalid route only if it receives a routing update that contains a better routing metric for the invalid route. If RIP does not receive a better metric for the invalid route until the hold-down timer expires, RIP advertises the invalid route to its neighbors till the flush timer expires. The invalid route will be removed, once the flush timer is expired.
Both the root invalid-route timer and hold-down timer work similarly except how they are triggered. An invalid-route timer of the route is triggered when RIP does not receive a routing update for that route until 180 seconds. The hold-down timer of a route is triggered when RIP receives a routing update that indicates that the route has become invalid.
That's all for this tutorial. In the next part of this tutorial, we will understand the split-horizon and route poisoning features of the RIP protocol. If you like this tutorial, please don't forget to share it with friends through your favorite social network.
