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

[Pat Calhoun (pacalhou) (pcalhoun]

All,

It has come to my attention that the following sentence should be
added to the new NAT considerations text:

11.  NAT Considerations
[...]
   A protocol interoperability issues will exist if the NAT
   system is being utilized for IPv4/IPv6 address translation.

Pat Calhoun
CTO, Wireless Networking Business Unit
Cisco Systems

 

> -----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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