Hi Jukka, Are you saying that the receiving GUT recalculates the DCCP checksum? But the only effect that would have is to make any errors introduced on the way undetectable. Tom P. > -----Original Message----- > From: Jukka Manner [mailto:jukka.manner@xxxxxx] > Sent: Tuesday, April 13, 2010 12:58 AM > To: Phelan, Tom > Cc: Colin Perkins; DCCP working group > Subject: Re: I-D Action:draft-ietf-dccp-udpencap-00.txt > > Yes, that's right. Except that GUT itself recalculates the checksum > before the packet hits the DCCP receiver. Thus, the UDP-encapsulated > DCCP flow never needs to do anything - it never even sees that GUT was > there. > > regards, > Jukka > > On 12.4.2010 23:17, Phelan, Tom wrote: > > Hi Jukka, > > > > Well, I guess one of us misunderstands something, because it looks to me > > like GUT doesn't work. Taking your example in section 3.3 of the draft: > > > > We start out with a DCCP packet encapsulated in IP as: > > Dest addr (DA): B > > Src addr (SA): A > > DCCP Ports : E and F (I assume that's what your notation means) > > DCCP checksum calculated over contents of DCCP packet and IP > > pseudo header with DA/SA = B/A > > > > This packet gets GUT'd as: > > DA: B > > SA: A > > UDP Ports: E and GUT > > DCCP packet unchanged > > > > This packet gets NAT'd as: > > DA: B > > SA: C > > UDP Ports: P and GUT > > DCCP Packet unchanged > > > > This packet arrives at the remote host and gets un-GUT'd as: > > DA: B > > SA: C (!) > > DCCP packet unchanged > > > > And this packet fails DCCP checksum because the Source Address (C) is > > different now than when the checksum was calculated initially (with SA = > > A). > > > > What am I missing? > > > > Tom P. > > > > > >> -----Original Message----- > >> From: Jukka Manner [mailto:jukka.manner@xxxxxx] > >> Sent: Monday, April 12, 2010 3:21 PM > >> To: Phelan, Tom > >> Cc: Colin Perkins; DCCP working group > >> Subject: Re: I-D Action:draft-ietf-dccp-udpencap-00.txt > >> > >> > >> DCCP wouldn't need to care about checksums if we had a generic > >> encapsulation scheme, such as the one we have been discussing on the > > TSV > >> list, the Generic UDP Tunneling scheme GUT. > >> > >> Jukka > >> > >> On 04/12/2010 06:05 PM, Phelan, Tom wrote: > >>> Hi All, > >>> > >>> OK, I'll accept the apparent consensus and make the DCCP header the > > same > >>> format in both encapsulations. Note that a DCCP implementation is > > still > >>> going to need to know whether this came in with UDP encap or STD > > encap > >>> -- the checksum processing needs to be different at least. > >>> > >>> Tom P. > >>> > >>>> -----Original Message----- > >>>> From: Colin Perkins [mailto:csp@xxxxxxxxxxxxx] > >>>> Sent: Sunday, April 11, 2010 5:55 AM > >>>> To: Phelan, Tom > >>>> Cc: Pasi Sarolahti; DCCP working group > >>>> Subject: Re: I-D Action:draft-ietf-dccp-udpencap-00.txt > >>>> > >>>> On 7 Apr 2010, at 15:14, Phelan, Tom wrote: > >>>>>> -----Original Message----- > >>>>>> From: Pasi Sarolahti [mailto:pasi.sarolahti@xxxxxx] > >>>>>> Sent: Thursday, February 18, 2010 5:54 PM > >>>>>> To: DCCP working group > >>>>>> Cc: Phelan, Tom > >>>>>> Subject: Fwd: I-D Action:draft-ietf-dccp-udpencap-00.txt > >>>> ... > >>>>>> * worth considering a straight UDP encapsulation that does not > >>> adjust > >>>>>> the position and order of the fields. > >>>>>> -- Gorry / 2009-11-20 > >>>>>> > >>>>> [Tom P.] Worth considering, but since there are already two > >>>>> implementations of the existing encapsulation I'm going to resist > >>>>> this. > >>>> > >>>> > >>>> We're early enough in the life of DCCP that I'd prefer we get this > >>>> right, than preserve running code that has minimal deployment. > >>>> > >>>> -- > >>>> Colin Perkins > >>>> http://csperkins.org/ > >>>> > >>>> > >>> > >> > >> -- > >> Jukka MJ Manner, Professor, PhD. Phone: +358+(0)9+470 22481 > >> Aalto University Mobile: +358+(0)50+5112973 > >> Department of Communications Fax: +358+(0)9+470 22474 > >> and Networking (Comnet) Office: G320a (Otakaari 5A) > >> P.O. Box 13000, FIN-00076 Aalto E-mail: jukka.manner@xxxxxx > >> Finland www.netlab.hut.fi/~jmanner/
