The RLNH Feat_neg_string is sent once by both peers to negotiate what features enable. It is contained in the INIT_REPLY message. The RLNH Feat_neg_string contain a string with all feature names and corresponding arguments. Only the features used by both peers (the intersection) are enabled. All the features supported by none or one peer (the complement) are disabled by both peers. An optional argument can be specified and It is up up to each feature how the argument is used and how the negotiation of the argument is performed.