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New Member

Default route& EIGRP

Hello!

1)if i use a default route along with EIGRP;IS The Default route win over EIGRP?

2)does The Default route in this case Acts as a Back up route if EIGRP Fail?

10XS For ur Valuable Info

7 REPLIES
Cisco Employee

Re: Default route& EIGRP

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
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: Default route& EIGRP

Hi Hritter!

plz explain this:The longest match rule still applies. So the EIGRP route wins if it is more specific than the default

10xs

Cisco Employee

Re: Default route& EIGRP

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
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Cisco Employee

Re: Default route& EIGRP

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,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

Re: Default route& EIGRP

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.

New Member

Re: Default route& EIGRP

Hi Mohamad!

10xs for ur reply!can u explain this:as the routing process prefers more specific routes over default routes:

10xs

Re: Default route& EIGRP

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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