BGP:Using local pref instead of BGP conditional route advertisement

Unanswered Question
May 25th, 2007

Imagine I want to make 3750_SWITCH pick RouterC as a path in case traffic from RouterB fails.

3550 switch:

router bgp 65123

neighbor [router b] remote-as [as #]

neighbor [router c] remote-as [as #]

neighbor [router b] route-map local-pref

route-map local-pref

set local-preference 200

Is there any drawback if I use 'local preference' attribute in order to control path the 3750_SWITCH should take ? I have been taking a look at 'Conditionally Advertising BGP Routes' as well. However, it seems to me that the 'local preference' method below should work and it is simple to implement.

If you think there is a relevant technical reason not to use the local preference method below and instead I should use BGP conditional route advertisement, please let me know.

Internet-RouterB---->3750_SWITCH<-----RouterC--Internet

I want to make 3750_SWITCH pick RouterC in case traffic from RouterB fails.

3550 switch:

router bgp 65123

neighbor [router b] remote-as [as #]

neighbor [router c] remote-as [as #]

neighbor [router b] route-map local-pref

route-map local-pref

set local-preference 200

I have this problem too.
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Richard Burts Fri, 05/25/2007 - 07:42

Marlon

For what you are doing I believe that local preference is the better thing to do.

HTH

Rick

John Patrick Lopez Fri, 05/25/2007 - 08:04

If both Router B and C advertises the same routes, you can also try to use weight. Setting a higher weight pointing to Router B.

HTH,

John

Edison Ortiz Fri, 05/25/2007 - 14:51

For your requirement, I recommend using both (local preference at the 3550 switch and conditional advertising at both routers).

Without conditional route, the routers will always advertise the default route even if their links are down, I'm assuming you don't want that.

The local preference on this case it's only assisting on the route selection of both default routes when both routers have the link up (they will both announce 0.0.0.0 back to you).

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