Maximum Hops

RIP imposes a hop count of 15 to help prevent routing loops which can occur when bad (for example, stale) routing information is broadcast and propagated through a network either due to misconfiguration, or slow convergence. Consider if the link between Router D and Router E failed in the example in Maximum Hops, and there were no safeguards in place:

• Router A’s routing information states that it can reach Network E through Router B or Router C with a metric of 3.
• When the link between Router D and Router E fail, and Router A broadcasts its routing information, Router B and Router C determine that they can reach Network E through Router A with a metric of 4.
• Router B and Router C broadcast this information, and it is received by Router D which then determines it can reach Network E through Router B or Router C with a metric of 5.
• This loop continues until the hop count of 16 (infinity) is reached.

Other measures against this sort of situation are also commonly employed by RIP, including:

• Split-HorizonRouting Table Updates
• Poison Reverse
• Routing Table Updates
• Subnet Sizes Supported
• Autonomous System Topologies