Some observations: - the title is misleading; this is TRILL over UDP, not trill over IP. - the use of two different ports invites some potentially unintended problems, e.g., selective blocking of the control vs. data plane. IMO, given that TRILL's purpose is to extend Ethernet (not IP), this service would be better served using a single port and differentiated encapsulated traffic by whatever method TRILL nodes use internally. Otherwise, this spec needs to include specific description of unexpected behavior, e.g., data frames on the IS-IS port and IS-IS frames on the data port. - regardless of whether one or two ports are requested, this doc should provide the needed information for IANA (e.g., a service name and description compliant with RFC6335). - the section on MTU handling might benefit from informationally citing intarea-tunnels, and consider using the recommendations there. In particular, it's not sufficient to assume IPv4 supports 576 byte MTUs (that's the minimum receiver reassembly MTU, not the transit MTU). That section should also address issues of PMTUD and PLMTUD. FWIW. Joe