I monitor about 150 routers with MPLS links.
To check if connection is established, I'm pinging loopbacks visible only from WAN. If a loopback is not responding, I can see which link is not working properly.
What are better possibilities? Pinging public address is not possible, as I noticed, and, sometimes, I still have router-edge router connection, but BGP is not established.
What are other monitoring options?