Default route& EIGRP

Unanswered Question
Harold Ritter Thu, 05/03/2007 - 11:53

1) The longest match rule still applies. So the EIGRP route wins if it is more specific than the default.


2) Yes.


Hope this helps,

Harold Ritter Thu, 05/03/2007 - 12:03

The router always tries to find the most specific route in the routing table matching the destination IP address of the packet to forward. So any matching route more specific than the default route will win.


Hope this helps,

Harold Ritter Thu, 05/03/2007 - 12:10

Just as a precision, when I say more specific route I mean a route with a longer prefix length. The default route is expressed as 0/0 as a prefix length of 0. The default route is by nature the least specific route you can get in the routing table.


On the other hand, a host route is the most specific route you can get as it has a prefix length of 32 and would be expressed as 192.168.1.1/32 for instance.


Hope this helps,


mohammedmahmoud Thu, 05/03/2007 - 11:55

Hi,


The default route won't won against the more specific routes received via EIGRP, as the routing process prefers more specific routes over default routes.


Yes, if you use a default static route with EIGRP, the default route will definitly work as a backup if the EIGRP fails.



HTH, please rate if it does help,

Mohammed Mahmoud.

mohammedmahmoud Thu, 05/03/2007 - 12:08

Hi,


The routing process does a 3 steps route selection:


1.Prefer longest match route first (more specific routes are preferred over less specific routes, and the default routes are the least specific routes).

2.Prefer Routes from lower AD routing protocol.

3.Prefer Routes with the lowest metric if they are received by the same routing protocol.


As an example for the more specific case, lets say a packet having a destination of 192.168.99.2, and the router has 2 routes one for 192.168.99.0/24 subnet and another for 192.168.0.0/16 subnet, according to the longest match concept, the router will choose the 192.168.99.0/24 route.


I hope that i've been informative.


HTH, please rate if it does help,

Mohammed Mahmoud.

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