Hello Binod
In the example in the lesson, the 2.2.2.0/24 network was advertising a hop count of 16. Such a problem with RIP would be seen in a very large network where the routers are actually 15 or more hops away from each other. However, for the purpose of this lesson, and to simplify the diagrams, Rene used two routers, but simulated a hop count of 15 using the offset-list command.
In RIP, the offset command is simply a way to manually set the metric of a particular network. It offsets the actual hop count by the value indicated. Specifically, the syntax of the command is:
offset-list {access-list-number | access-list-name} {in | out} offset [interface-type interface-number]
If a value of 0 is used for the access-list number, then it is applied to all traffic. The in/out value refers to the direction that the offset is applied in, and the offset is the value added to the actual metric.
So the command offset-list 0 out 15 actually adds 15 to any metric in any RIP messages that are sent out of R2, thus reaching R1 with a metric of 16.
The offset-list command was used here only for convenience, but it is useful in adjusting the behaviour of RIP. One specific use is to deal with the GRE tunnel recursive routing error that is described in the following lesson:
I hope this has been helpful!
Laz