iBGP & 2x eBGP

RouterOS Forwarding Protocols
1

Hello,

I have newbie question about iBGP configuration, please give some HOWTO.

Now we have:

  • 1 office, 1 router and 1 EBGP session with our ISP;
  • one AS-number and /22 IPv4 network.

We need:

  • create an additional eBGP session to ISP in another town;
  • rise up IGP between routers for exchanging routes;
  • use one /24 subnet from our /22 subnet in new place. For example, we have 192.168.96.0/22 from RIPE, in first place we use 192.168.96.0/24 , in second office we need to use 192.168.97.0/24


    I created iBGP with default settings(Remote IP, my AS) and it was successfully established.
    Then i started eBGP session with ISP in second office, but after that all my subnet 192.168.96.0/24 stop working from first office.

All my /22 network start working from new place, but in routes on router1 i have only reconfigured 192.168.96.0/24 and on router2 192.168.97.0/24

Thanks for any advice!

2

What prefixes you are advertising to each provider? Looks like you are advertising /22 from both peers and new one is more preferred.

3

Hello,

It is the same provider, in 2 different places.
Yes, i am advertising /22 subnet from both places. It is how it was received from RIPE.

4

There is a way to resolve situation if we advertising /22 network from both places?

5

Review this to see if it helps you in your design.

http://mum.mikrotik.com/presentations/HU11/linktech1.pdf

6

Advertise the /22 on both routers.
Then advertise each /24 on their “preferred” router. So in your case, the first 3 /24’s will be on router 1 and then 4th one on router 2.

All /24’s are smaller network blocks, they will be the preferred router over BGP. However if one router goes down, traffic will use the /22 on the other router as redundancy.

7

Why you do not advertise /24 subnets from their real place, mean 3X/24 from one side and one / 24 from another? Provider will advertise further as one /22 (summarized). But on it’s iBGP it will have 4 routes to you!