With DMPVPN does multiple NBMA addresses being the same cause instabilty.

[Michael Couture]

If you have 20 spokes all connected to a hub and multiple spokes have the same NMBA does it matter? I am new to DMPVPN and I am working on a configuration where all the spokes are connected behind Comcast or Fios and each site is using the cable/Fios modems default network configuration. This causes multiple spokes to have the same NBMA IP addresses. There are times when tunnels drop and it seems like the ones that have the same NBMA address as another spoke have issues coming back up. Is this a normal configuration of should the networks be changed so each site will not have overlapping NBMA addresses?

[jiandliu · Accepted solution]

I believe this is not supported because when Hub try to send a packet to a spoke, it may probably see a loadbalance entry and end up no idea which spoke really received the packet. You can use Loopback interface as Spoke's Tunnel Source in order to have distinguished NBMA address for each Spoke.

[Michael Couture]

Jianda,

Thanks for the input and sorry for the delayed response. The loopback is a good suggestion. Seeing that the owner of each of the spokes is an IT professional and understands at least basic networking I had then all change there network from the default network that Comcast and Fios hand out. That ensured all parties had different NBMA addresses. Since that time I have had no issues with the Tunnels. That said I think in the future I will try using the loopback interface as the source and see how that goes.