On 5/26/2016 9:40 AM, Templin, Fred L wrote: > Hi Joe, > >> -----Original Message----- >> From: Joe Touch [mailto:[email protected]] >> Sent: Thursday, May 26, 2016 9:34 AM >> To: Templin, Fred L <[email protected]>; Tom Herbert >> <[email protected]> >> Cc: [email protected] >> Subject: Re: [Int-area] Call for adoption of draft-xu-intarea-ip-in-udp-03 >> >> >> >> On 5/26/2016 9:16 AM, Templin, Fred L wrote: >>>>>> There is an existing solution to the same problem. GUE allows >>>>>> encapsulation of IPv4 and IPv6, as well as other IP protocols (the GUE >>>>>> header indicates encapsulated protocol by IP number). The only >>>>>> material between GUE encapsulation of IP and IP in UDP is additional >>>>>> four byte header and associated processing of that. I don't think >>>>>> we've seen a use case where avoiding that overhead is critical >>>>>> motivation. >>>>> I thought at one time we had come up with an idea for omitting the GUE >>>>> header when the payload is a plain IPv4/IPv6 packet. There was a check >>>>> of the first four bits following the UDP header to see if they encoded the >>>>> value '4' or '6'. Did that not make it into the draft? >>>>> >>>> Yes, we had come up with the idea and I have implemented the >>>> prototype. It is not in the draft. I believe the only discernible >>>> benefit we could identify was that it saves 4 bytes of overhead. The >>>> major drawback is that this only works specifically for IPv4 and IPv6. >>> I don't see the drawback; I think those two IP protocol versions could >>> carry us forward into the forseeable future. Are you thinking there >>> could be another IP version on the near term horizon? >> IMO, this is a bad idea unless the protocol is specifically limited to >> having IP as a payload. Otherwise, there's no way to ensure that some >> other protocol won't start off with those values. > Tom's proposal unambiguously differentiates raw IPv4 and IPv6 from > all other encapsulations. If it is raw IPv4 or IPv6, the GUE 4-byte header > is not present. Otherwise, the GUE 4-byte header is present. > The only way the proposal "unambiguously" knows the difference is when the first 4 bits are 4 or 6, but those are valid configurations of the first 4 bits of other protocols (notably ICMPv4).
So if you see 4 or 6, you can't just assume that the GUE header is not present. Joe _______________________________________________ Int-area mailing list [email protected] https://www.ietf.org/mailman/listinfo/int-area
