BGP question. How to advertise some routes with as-path prepend ans some without/

Answered Question
Feb 10th, 2010
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I am trying to configure a scenario where we are BGP peering with the same provider in two locations, our main location and our DRC.  We want to advertise


10.10.10.0/26 out of our HQ and

10.10.10.128/26 out of our DRC.


At the same time we want to ensure failover by advertising


10.10.10.128/26 out of our HQ with an as-path prepend and

10.10.10.0/26 out of the DRC with an as-path prepend.


How can I make that happen?  I can only choose one route-map for out going advertisements, so if I use a as-path prepend it applies it to all advertisements.


Is there a way to make this possible?


Thanks

Joerg

Correct Answer by Giuseppe Larosa about 7 years 2 months ago

Hello Jeorg,

route-maps can be made of multiple blocks each with its own match and set commands so this is the way to go


route-map toISP permit 10

match ip address 10

set as-path-prepend MyAS MYAS

route-map toISP permit 20

match ip asddress 11

! no set action is allowed


even an empty final block can be used


you can use an ACL or a prefix-list for each block




Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Wed, 02/10/2010 - 14:15
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Hello Jeorg,

route-maps can be made of multiple blocks each with its own match and set commands so this is the way to go


route-map toISP permit 10

match ip address 10

set as-path-prepend MyAS MYAS

route-map toISP permit 20

match ip asddress 11

! no set action is allowed


even an empty final block can be used


you can use an ACL or a prefix-list for each block




Hope to help

Giuseppe

joerggrau Wed, 02/10/2010 - 14:34
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Yep.  that works.


Thanks a lot.


Now I need to figure out how to get these kinds of routes injected into either eigrp or ibgp and to retain the weights...


I'll go and play.  Will let you guys know if I need some more pointers.


Thanks

Joerg

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