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

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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
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