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VIP Purple

BGP AS PATH issue

Hello colleagues,

let´s say I have three routers (R1, R2, R3) all in different BGP ASs. I want to accomplish that R3 sees routes coming from R1 as originating from R2. I have tried route aggregation with summary-only on R2, but then only the summarized routes originate in the R2 AS, not the original routes coming from the R1 AS. Has anybody tried that ?

Thanks for your help in advance.

Regards,

Georg

6 REPLIES
New Member

Re: BGP AS PATH issue

Hi,

Kindly try to provide a diagram with your 3 routers in different AS's.

Rgds,

Homin

New Member

Re: BGP AS PATH issue

Hi,

I think you can run BGP with R1 and R2 , advertising routes orginating from R1 to R2 and inturn run BGP with R2 and R3.This will enable R2 to advertise the learned routes from R1 to R3. You have not supplied broad view of what exactly you try to achieve. Hope this answer will shed some light.

Rgds,

Homin

VIP Purple

Re: BGP AS PATH issue

Hello,

here is a diagram:

R1 (AS100) -- R2 (AS200) -- R3 (AS300)

R1 advertises 155.100.200.7, this is seen by R3 with an AS PATH of 200 300. I want R3 to see this route with an AS PATH of just 200. I have tried the aggregate command with the summary-only option on R2, but that only advertises 155.100.0.0 to R3.

Hope this sheds some light on what I want to achieve.

Georg

Silver

Re: BGP AS PATH issue

Here are two solutions that may help you:

1. If possible, you can config a private AS number, say 65000, for AS 100. Then you can use remove-private-AS on R2. This will propagate R1 routes to R3 as being originated from only AS200.

2. AS-PATH can also be changed by first redistributing eBGP routes into IGP and then redistributing IGP paths to BGP. You can also define static routes, if possible, between 100 and 200 and redistribute those prefixes to BGP.

Hope this helps.

Silver

Re: BGP AS PATH issue

BTW, your aggregate solution should work as well.

rais.

Re: BGP AS PATH issue

In case you cannot change the AS no to private AS, and strip it off using "remove-private-as", you can do one thing.

Try configuring the aggregate with the specific route network/mask itself. (say for example, 150.1.1.0/24, should be actually aggregated as 150.1.0.0/16, say, instead use the aggregate network and mask as 150.1.1.0/24)

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