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Beginner

BGP - How to create redundant path by bgp (as path prepend alternative)

I am having issues with BGP seeing the advertised routes. I am trying to find an alternate to AS-Path prepend and trying to use bgp instead for a redundant path.

 

Setup:-

We have 3 mpls sites. (in reality its more than 20 but for simplicity we will call that 3).  The 3 sites are SiteA , SiteB and siteC.  I have simplified the issue below.

 

SiteA - Has MPLS link running eBGP with AS 300.

SiteB - Has MPLS link running eBGP with AS 200

SiteC- Has MPLS link running eBGP with AS 100

 

Site B and C has a local LAN connection between each other.  Site A and B and C are on BGP network. Site A can see B and C and so on.

Issue:

I have established eBGP neighbor relationship between B and C using multihop using the private link between two private interface ip address. I can see them as neighbors.

When i advertise the network of site B at site C i see that in the advertised routes on site C when i run sh ip bgp nei x.x.x.x advertised-routes but i don't see that at site A when i run "show ip bgp"

From Site A:

When i run show ip bgp : I was expecting to see...

 

20.20.20.20  - is reachable as As200 -i

Also..

20.20.20.20  - As100 - 200 - i  (i don't see this)

 

That way it will be a backup path instead of using as-path prepend.

 

Can you throw some ldeas as to what i am missing. If i am not clear enough let me know and i will provide more details.

 

Everyone's tags (1)
2 REPLIES 2
VIP Advisor

Hellowhen you say "advertise

Hello

when you say "advertise network from site B at site C"

how are you doing this.?

For a route to be advertised in bgp it's need to be in the rib of the advertising router

so if you have just applied a network statement (bgp table) for site B at site C and site C route doesn't have a valid prefix in its routing table it won't get advertised to site A

 

Site C router

Sh ip route x.x.x.x

sh ip bgp x.x.x.x

 

res

Paul



kind regards
Paul

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Beginner

Thanks for responding. i have

Thanks for responding. i have added a prefix list for filtering outbound. I was hoping that it will learn that route through the bgp network statement.

 

ie.. I have added network B at C and network C at B. They both are neighbors and when i see advertised routes and received routes i can see the routes. 

 

How should i proceed or any guidance would help..

 

From site C i want to see below when i do show ip bgp for 20.20.20.20.

 

20.20.20.20  - is reachable as As200 -i

20.20.20.20  - As100 - 200 - i  (i don't see this)

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