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Posts: 40
Joined: Sat Sep 27, 2014 8:10 am

send prefix only from 1 upstream to transit

Thu Jul 13, 2017 1:06 pm

i'm completely new in BGP and spent many times to find out in this forum and google but still no luck to found the proper way.

lets say my BGP router CHR has 2 transit peering from upstream A and upstream B, each of them gives full routes. from this, my router learns the best path to particular destination ip and it should many inactive routes to other destination ip from upstream A and upstream B depend on which one is best path.

here is /ip route sample from my simulation, CHR with 2 upstream and 1 transit service.

network has 2 gateway upstream A and upstream B. in order to give upstream B only, i have create out filter and discard all routes from upstream A to transit service client, but due to CHR has with gateway from upstream A, transit service client didn't receive route

my question is what is the proper way to give all routes learned from upstream B even some routes are inactive at routing table on CHR?

thank you for answer.
Posts: 40
Joined: Tue Nov 20, 2012 12:05 am

Re: send prefix only from 1 upstream to transit

Fri Jul 14, 2017 10:23 am

I'm not familiar with the BGP process in Mikrotik, but you can degrade for example you transit B adding repeatedly your AS in the AS-PATH via prepend. Take a look at that.

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Re: send prefix only from 1 upstream to transit

Sun Jul 16, 2017 3:43 pm

I gather that you want to give the transit customer a view of internet and only tell one of your transit providers that the transit customer is reachable through you.

If so then: Take the learned routes from your transit customer append them with a community that you staple only transit type A and then apply corresponding filters only matching your prefixes and that community from other transit customers.

As for Mikrotik announcing routes that are not active is another story. RIB and FIB are not disconnected thus its impossible to to "real" Route reflection in that manner. But I'd say that is not a problem in your view.

You which to give transit customer your view of internet. Check he got that which ever peer you have chosen building your view. ( He got the Complete View, But you chose how traffic exits your network that's not up to the transit customer to decide.
Only Your transit provider type B would se the path: Check that is solved with above community magic thus you give other AS'es on the internet the Ability to Chose if that is a good way or not.

You can decide how incoming traffic is sent through your network:
You can ask internet to consider sending traffic to you at a desired path but that is not guarantied.
Internet Routing is Inherent Asymmetrical Incoming and outgoing need not and often are not the same paths at all.

As a transit provider you must take into account that other Ip's than announced may source traffic and set all Rules accordingly. Plan building for both transit, peering and end customers all having different set of rules int that chapter of doctrine.

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