Detecting excessively long routes

Detecting excessively long routes

8.1.6 This page will explain how excessively long routes are created.

Situations can occur in network communication where a datagram travels in a circle, never reaching its destination. This might occur if two routers continually route a datagram back and forth between them, thinking the other should be the next hop to the destination. When there are several routers involved, a routing cycle is created. In a routing cycle, a router sends the datagram to the next hop router and thinks the next hop router will route the datagram to the correct destination. The next hop router then routes the datagram to the next router in the cycle. This can be caused by incorrect routing information.

The limitations of the routing protocol can result in unreachable destinations. The hop limit of RIP is 15, which means that networks that are greater than 15 hops will not be learned through RIP.

In either of these cases, an excessively long route exists. Whether the actual path includes a circular routing path or too many hops, the packet will eventually exceed the maximum hop count.

The next page will discuss ICMP messages