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

Colin Perkins <csp@xxxxxxxxxxxxx> · Sun, 11 Apr 2010 10:53:52 +0100

On 7 Apr 2010, at 19:02, Pasi Sarolahti wrote:

On Apr 7, 2010, at 7:26 AM, Phelan, Tom wrote:

Have the benefits vs. disadvantages of defining a different DCCP
header for UDP encapsulation been discussed earlier? The current
method saves some redundant header space, but may add to
implementation complexity in the DCCP side. I can't say if this is a
significant concern, but I wonder if it is a problem that DCCP-UDP
supports different set of features than native DCCP, such as not
supporting the short sequence numbers?

[Tom P.] The purpose of short sequence numbers in DCCP-STD is to  

reduce

header length.  Supporting short sequence numbers in DCCP-UDP doesn't
reduce the header size.  The purpose of long sequence numbers in
DCCP-STD is to reduce the probability of a blind attacker correctly
guessing the sequence numbers in use.

So in my view short sequence numbers are more of a bug than a  

feature,

and not supporting them in DCCP-UDP is the better solution.

Ok, this is fair reasoning. But still, as a matter of design  

principle, I think it is a little unusual that when receiving a  

packet for a protocol, the receiver would need to consider what was  

the previous header in order to parse the current protocol header.  

Ideally one might want to use the same DCCP implementation  

regardless of whether the packets go inside IP or UDP. But I'd be  

interested to hear what others think.

Agreed. The fewer changes that are required to run DCCP over UDP than  

over IP, the better. I'd greatly prefer the DCCP header to be  

identical in both cases, since it simplifies implementations.

--
Colin Perkins
http://csperkins.org/