 - Route poisoning is a method of preventing a network from sending packets
through a route that has become invalid. When the routing protocol detects
an invalid route (such as can be caused by a severed cable or the failure of
a network node), all of the routers in the network are informed that the bad
route has a hop count of 16, which stands for infinity. This makes all nodes
on the invalid route appear infinitely distant, thereby preventing any of
the routers from sending packets over the invalid route.
When the path between two routers in a network goes bad, all the routers
in the network are informed immediately. However, it is possible for this
information to be lost, causing some routers to once again attempt to send
packets over the bad route. This requires that they be informed again that
the route is invalid, and again, this information can be lost. The resulting
problem is known as a routing loop. Route poisoning is used in conjunction
with holddowns. A holddown keeps update messages from falsely reinstating
the validity of a bad route. This prevents routing loops, improving the
overall efficiency of the network.
| CONTRIBUTORS: |
Karl Wick |
| LAST UPDATED: |
18 Apr 2007
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