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BGP Conditional advertisement

illusion_rox
Level 1
Level 1

Hi all, kindly refer to this document

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a0080094309.shtml

now if i want this

If 192.168.50.0/24 exists in R102's BGP table, then do not advertise the 128.16.16.0/24 network to R101.

how can i accomplish this ? if i want to block advertisement of certain prefix when a particular prefix is in the BGP table then how can i do that ?

Thanks

7 Replies 7

Harold Ritter
Cisco Employee
Cisco Employee

Ovais,

This is exactly what the example does, as per comments in the configuration example:

!--- Advertises the routes matched in the route-map ADVERTISE (128.16.16.0/24)

!--- only if the routes matched in route-map NON-EXIST (192.168.50.0/24)

!--- do not exist in the BGP table.

So if 192.168.50.0/24 is present, 128.16.16.0/24 will not be advertised.

If you wanted the opposite (i.e. advertise 128.16.16.0/24 only when 192.168.50.0/24 is present) then you would use an exist-map instead of a non-exist-map.

Regards,

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

cisconoobie
Level 2
Level 2

Try this. I'm not at a router to test but see if it works for you.

access-list 60 permit 128.16.16.0 0.0.0.255

access-list 65 permit 192.168.50.0 0.0.0.255

route-map EXIST deny 10

match ip address 65

route-map ADVERTISE permit 10

match ip address 60

neighbor 10.10.10.1 advertise-map ADVERTISE exist-map EXIST

Again, try this in a test environment as I didn't have a chance to test this myself.

Sparky,

This configuration would advertise 128.16.16.0/24 if 192.168.50.0/24 exists.

From the original poster:

"if i want to block advertisement of certain prefix when a particular prefix is in the BGP table:

Sounds like the opposite, right?

Regards,

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

I guess, I was just giving ideas.

hi guys, i got it done :) i was a bit confused but still did it, one thing for sure is that we cant use deny statements in any route-map ( advertise, exist and non-exist ) right ??

Ovais,

That is correct. You need to work either with the exist-map or non-exist-map but the trigger has to be done on a permit.

Regards,

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

Sparky,

Understood. Thanks for your contribution to NetPro.

Regards,

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
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