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Re: I-D Action:draft-ietf-dccp-udpencap-00.txt



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/


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