From a security perspective, it is possible to leverage the IS-IS HMAC-MD5 authentication feature to add an HMAC-MD5 digest to each OTV control protocol message. The digest allows authentication at the IS-IS protocol level, which prevents unauthorized routing message from being injected into the network routing domain. At the same time, only authenticated devices will be allowed to successfully exchange OTV control protocol messages between them and hence to become part of the same Overlay network.
Once OTV edge devices have discovered each other, it is then possible to leverage the same mechanism to exchange MAC address reachability information