Capwap Mailing List: Re: Proposed Text for Issue 249: IPv6 UDP Lite

[Abhijit Choudhury (achoudhu) (achoudhu]

In addition, the text and packet format figures in Section 4
need to be updated to include UDP or UDP-Lite.


Thanks,
Abhijit
 
 

-----Original Message-----
From: Pat Calhoun (pacalhou) 
Sent: Monday, March 19, 2007 2:26 AM
To: capwap [at] frascone.com
Subject: [Capwap] Proposed Text for Issue 249: IPv6 UDP Lite

All,

In the event that the WG agrees that we are to proceed with this change,
I would like to submit proposed text to the list. As discussed on the
mailing list previously, UDP-Lite would be restricted to IPv6. Yes, it
does have some NAT transversal issues, which is why some text was added
to the NAT Considerations section. However, there are no IPv6 NATs
today, so there is nothing legacy broken in this proposal. Note that I
also added the proper reference to UDP number assignment in the IANA
considerations as well.


3.  CAPWAP Transport

   Communication between a WTP and an AC is established according to the
   standard UDP client/server model.  The CAPWAP protocol supports two
   different transport protocols.  When used over IPv4, the UDP protocol
   is utilized.  When CAPWAP is used over IPv6, the UDP-Lite RFC 3828
   [13] is used.  This section details the specifics of how the CAPWAP
   protocol works with IP.

3.1.  UDP Transport

   One of the CAPWAP protocol requirements is to allow a WTP to reside
   behind a firewall and/or Network Address Translation (NAT) device.
   Since the connection is initiated by the WTP (client) to the well-
   known UDP port of the AC (server), the use of UDP is a logical
   choice.  The UDP checksum field in CAPWAP packets MUST be set to
   zero.

   CAPWAP protocol control packets sent between the WTP and the AC use
   well known UDP port [to be IANA assigned].  CAPWAP protocol data
   packets sent between the WTP and the AC use UDP port [to be IANA
   assigned].

3.2.  UDP-Lite Transport

   When CAPWAP is run over IPv6, the UDP-Lite is used as the transport.
   The reason for using UDP-Lite is because when UDP is run over IPv6,
   it MUST NOT have its checksum field set to zero, which increases the
   processing cost for each CAPWAP packet.  When UDP-Lite is used, the
   checksum field MUST have a coverage of 8 RFC 3828 [13].

   As defined in RFC 3828 [13], UDP-Lite uses the same port assignments
   as UDP.
[...]

11.  NAT Considerations
[...]
   When CAPWAP is run over IPv6, NAT support can only be provided if the
   IPv6 NAT system is capable of performing address translation over the
   UDP-Lite 3828 protocol [13].

[...]
14.  IANA Considerations

   A separate UDP port for data channel communications is (currently)
   the selected demultiplexing mechanism, and a port must be assigned
   for this purpose in section Section 3.1.  The UDP port numbers are
   listed by IANA at http://www.iana.org/assignments/port-numbers.


Pat Calhoun
CTO, Wireless Networking Business Unit
Cisco Systems
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