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Nevon
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Force a certain IP subnet a certain path with multiple BGP peers.

Tue Mar 15, 2022 8:41 am

Can I force a certain IP subnet a certain way in and out if I have several BGP peers.
So I want to prioritize a certain Peer for this subnet.

Possible?
 
eduplant
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Re: Force a certain IP subnet a certain path with multiple BGP peers.

Tue Mar 15, 2022 9:27 pm

Technically it’s possible as long as the prefix you want to advertise is shorter (in terms of bit length) than the longest your peers will accept (usually /24). Since IP is destination-routed, it isn’t so much a BGP issue for outbound but you could policy route traffic from that network towards a particular exit.

Practically speaking, what are you trying to accomplish? It might be tempting to do this for load-sharing your links or something but remember that you have way less control over the path to you than you would within your own network.
 
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woland
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Re: Force a certain IP subnet a certain path with multiple BGP peers.

Tue Mar 15, 2022 10:03 pm

Hi Nevon,

in a basic setup:
-you do this inbound for any route with path prepend if you connect to multiple ASes (you add the same AS a few times, so that you have a longer path for that route over one of your routers)
-you can do outbound traffic steering with local preference
-if you connect to multiple routers from a single AS on the other side you can use MED to steer inbound traffic
There is more to it, the details are quite complicated, so I suggest you should read some docs.
I find one of the best free resources on BGP is from Juniper: https://www.juniper.net/documentation/u ... index.html

BR
W
 
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Nevon
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Re: Force a certain IP subnet a certain path with multiple BGP peers.

Wed Mar 16, 2022 8:26 am

Thanks!

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