Subject: [Softwires] L4 checksum spec in MAP-T

From: Maoke <[email-masked]>
Date: Thu, 15 Mar 2012 02:09:54 +0000

hi Woj, prof. Bao and others,

as i discussed with Remi in the thread
http://www.ietf.org/mail-archive/web/softwires/current/msg03641.html , i
found that RFC6145 leaving DCCP support as optional may cause a
asymmetric-process when it is applied for double translation, and there was
not an explicit statement on the support for other L4 protocols. i do
suggest to consider this issue in MAP-T. my humble suggestion is adding two
paragraph in the introduction, after the first paragraph, stating that:

   Regarding the L4 checksum calculation at the address-family boundary (CE
or BR),
   RFC6145 mandates TCP and UDP but leaves DCCP as optional. In a
double-translation
   environment, if only IPv4-to-IPv6 translator adjusts the checksum of
DCCP but the
   IPv6-to-IPv4 side doesn't, the IPv4 destination may receive DCCP packets
with wrong
   checksum. MAP-T ensures DCCP support by updating its checksum at CE or
BR whenever
   the DCCP packets are passing through.

   Listing all possible transportation protocols is not feasible nor
necessary. For
   a transportation protocol not mentioned explicitly here or in RFC6145, a
   MAP-T-compliant equipment MUST either discard packets of that protocol
(as
   unsupported) or have the corresponding code for the L4 checksum
adjustification.

   * Throughout this document, whenever RFC6145 is cited, the above
considerations
   are also involved, even without explicit statement.

if anyone thinks support of DCCP and/or other less-well-known
transportation protocols is fairly not significant, please also respond.
thanks a lot for the concern.

regards,
maoke