RIP v2 and Network Size

Nate sent the following message:

How many routers does RIP support? 
How about RIP version 2?
I see that your tutorial says 15 hops, 
but does that mean you can only
have 15 routers in your network?

The RIP protocol defines no limit on the number of routers it will support.  However, by setting a  limit on how long the network path between any two endpoints can be, there is a limit to how large a RIP routed network can grow.   The 15 hop limit comes from the fact that RIP v1 uses Split Horizon and poison reverse as part of the routing logic to eliminate loops within the network.  Split Horizon prevents a router from accepting a route it announced to someone else and if a RIP router recognizes such a route, it poisons it by setting it’s hop count to 16.

Because RIP v2 was designed to be backwards compatible with RIP v1, RIP v2 uses the same Split Horizon and poison reverse routing mechanism to prevent the creation of routing loops, which mandates the 15 hop limitation in RIP v2 as well.

As to the size of the network and number of routers, consider this drawing:

RIP Network Diagram

As you can see, there are 57 routers in this diagram. That’s a LOT more than 15 routers.  Note that no router is more than 15 hops from any other router.   If you continue along on this design, you could continue to add chains of 7 routers from the core router for as long as there are network ports available and grow this network larger still.

One important note:  this diagram was created just to demonstrate a point.  You should never design or construct a network with one core device that can take out the whole network when it fails such as would occur when the core router in this diagram failed.

So, while you can’t have any two endpoints more than 15 hops apart, you can have a lot of routers in a RIP network.