Multiple Peer sessions on the same IP address problem

RouterOS Forwarding Protocols
1

Hello,

We have a problem setting up multiple BGP sessions with the same (upstream) IP address. What we try to achieve here is to have two or more BGP sessions with the same IP address, but with different public AS numbers. For example:

Upstream peer is AS6238x
Peer IP is 185.23x.64.1

Downstream peers are: AS3951x and AS4887x.

When we try to add a second downstream peer to the same IP address of the upstream Peer, we get an error message:

Couldn’t change BGP Peer <name_here_2> - already exists (6)

Similary, when we try to establish on the upstream Peer router a downstream session with the two ASNs we get the following error:

Couldn’t change BGP Peer <name_here_2> - already exists (6)

Both routers are CCR1036 (for the Upstream and the Downstream as well).

What should we do ?

Thanks in advance!

2

Not possible, you can open only one TCP socket per IP scr/dst and port combination.

Local or remote address must be different at least on one of the routers.

3

Thanks for the reply. So i’ve figured, and from what we are trying at the moment, it seems that both local and remote IP addresses have to be different. This is not OK, because this means that for every BGP session we need to “sacrifice” at least 2 IP addresses. Any workaround for this ?

4

No, only one should be different source or destination, so only one address must be sacrificed.

5

Could you please show or link me towards an example of such ?

THanks

6

In my current setup (made before you started this thread) I have a /29 subnet in which my local router has connection from the same source address to two different destination addresses in that /29 network.
That works fine. These 2 destinations are 2 different routers in the same AS (different from the local AS).
That should not be different from 2 different AS that in fact are the same router.

7

We managed to add an extra IP on both ends (both routers) for the new BGP connect, however the issue that arises now is that the SECOND router is trying to connect to router ONE using a wrong IP address, the IP address belonging to the first BGP sessions. Here is the log detail:

Invalid remote AS, expected 3951X
RemoteAddress=185.23x.64.8
RemoteAs=48874

8

You should set the update source to the correct address…

9

Thank you! That was it! I entered the update source for each Peer with the IP with which they should use to update the session. So problem solved and everything is OK now!

10

Hi,
How do I change the local IP address? I tried to update it in Advanced-Update source field but still can’t establish secondary BGP session to the same remote AS. I have two links and need to establish a session with the same RS server over each of the links but giving different localprefs to them. Any way to achieve this? When I’m trying to copy an existing BGP peer and just change the update source I’m getting an error ‘Couldn’t add BGP peer - already exists’. Thanks.

11

You are replying to a very old topic, and things have changed a lot since then.
I would not know if that still works.