Hi Joe, > -----Original Message----- > From: Joe Touch [mailto:[email protected]] > Sent: Tuesday, May 05, 2015 11:26 AM > To: Templin, Fred L; Xuxiaohu; Donald Eastlake; [email protected] > Cc: [email protected]; [email protected]; [email protected] > Subject: Re: [trill] Fwd: Mail regarding draft-ietf-trill-over-ip > > > > On 5/5/2015 11:04 AM, Templin, Fred L wrote: > > Hi Joe, > > > >> -----Original Message----- > >> From: Joe Touch [mailto:[email protected]] > >> Sent: Tuesday, May 05, 2015 10:54 AM > >> To: Templin, Fred L; Xuxiaohu; Donald Eastlake; [email protected] > >> Cc: [email protected]; [email protected]; [email protected] > >> Subject: Re: [trill] Fwd: Mail regarding draft-ietf-trill-over-ip > >> > >> > >> > >> On 5/5/2015 9:39 AM, Templin, Fred L wrote: > >>> Hi Joe, > >> .. > >>>> IP in UDP adds only port numbers and an Internet checksum. > >>>> > >>>> That doesn't address fragmentation; if outer fragmentation is assumed, > >>>> IPv4 needs to be rate-limited to avoid ID collisions and the Internet > >>>> checksum is insufficient to correct those collisions. > >>> > >>> Right - that is why we have GUE. But, when these functions are not > >>> needed GUE can perform header compression and the result looks > >>> exactly like IP in UDP. > >> > >> That seems impossible. > > > > Not impossible - Tom Herbert provided the solution: > > > > http://www.ietf.org/mail-archive/web/int-area/current/msg04593.html > > That is allocating bits (or bit patterns) from the IP header. > > The solution provided - to check for 0x01 - is incorrect. IP can have > versions that include 0x10 and 0x11.
The version field in both IPv4 and IPv6 have that bit set to 1. If GUE then deems that bit to indicate "direct IP encapsulation, then there is no need for a GUE header of length greater than 0. You may say that future IP protocol versions might not have that bit set in the version field. But, the version bits for IPv4 and IPv6 will never change (by definition) and we do not see a new IP protocol version replacing IPv4 or IPv6 on the near-term horizon. Even if a new IP protocol version emerged with the "direct IP encapsulation" bit set to 0, that version can still be accommodated by GUE. It's just that direct encapsulation cannot be used and a non-zero-length GUE header is needed. Thanks - Fred [email protected] > The only solution would be to say that if the first three bits were 0, > then it's not an IP packet - but that would require reassigning 0x0000 > and 0x0001 for GUE purposes. > > Although that's possible, I don't see why we would allocate IP versions > to GUE message types. > > Joe _______________________________________________ Int-area mailing list [email protected] https://www.ietf.org/mailman/listinfo/int-area
