Thank you for your answer. You are right, the client router (v7.5) has 2 routes to the same IP address range over both VPNs. Both routes are coming from BGP:
Flags: D - DYNAMIC; X, I, A - ACTIVE; c, s, b, d, y - COPY; + - ECMP
Columns: DST-ADDRESS, GATEWAY, DISTANCE
# DST-ADDRESS GATEWAY DISTANCE
DAb+ 172.20.0.0/16 10.20.0.1 20
DAb+ 172.20.0.0/16 10.40.0.1 20
But because VPNs are established to 2 different offices, ECMP becomes a real issue. In earlier versions flag “+”, which is ECMP wasn’t there and everything was working perfectly. Since ECMP for BGP was implemented in (at least) v7.5, I thought there must be a way to stop / disable it per BGP connection.
Or, if I may, it could be a good idea not to start it automatically. If some one needs it, there might be an option to turn it on. For example, a router doesn't automatically create 4095 VLANs just in case if a user needs all of them.
If you make an adjustment to make it pick a single preferred path to the BGP nexthop, the resulting routes should follow.
That's what I'm talking about.
I don't know how to disable automatic multipath. The only adjustments I could think of is a work around using Mangle rules (and it works by the way), but this is really not a solution, this is just a band aid.
So, it would be great if someone tells me how to disable ECMP over BGP.
P.S. I know many people asked for ECMP for BGP. I’m not saying it’s a bad idea, I’d just like to know how to turn it off if need be.