I agree with @MijanurRahman With regard to existing addressing and new addressing - you will have to manually check each assigned subnet to make sure it does not conflict with existing addressing. Either that or just manually assign each subnet. Your next choice is weather to run AutoVPN over MPLS. This is my preferred solution, because it means you can detect a failure inside of the MPLS provider, and [if sites have a backup circuit] failover automatically. If you use this method you will want a stub network from the MPLS provider (such as a /30 or a /29) and the MPLS provider does not need to know about your site addressing. I prefer to use /29's because if you want to put in dual MX's at a site for HA you can. Sometimes the important of a site changes at a later point in time, and this makes upgrading it to HA easy. The other approach is to use a tracked router This is where you ping something [like the next hop] and then choose to use the MPLS as the primary interface [by selecting routes based on the track result] and something else for a backup interface. This method is easy, but it can't handle detecting a failure inside the MPLS cloud.
... View more