Often times nodes need to communicate with each other what their implementation is, looking for specific features that are only in select implementations, the desired feature is a question of node implementation.

A concept of Unspecified protocol extensions has been proposed, they are unspecified as they are not part of the BOLT specifications, each extension must have a set of random 20-byte identifier with type bigger than a certain number. Using the concept of current extension, any extensions that are unidentified by a node will not be recognized, while if the node’s implementation identifies this unspecified extension, both nodes can continue communications knowing that they have the same set of extra features.