Capwap Mailing List: CAPWAP transport for IPv6

[Abhijit Choudhury (achoudhu) (achoudhu]

At the last IETF, the transport A-Ds raised some interesting

issues related to the use of UDP-Lite for IPv6.  Specifically, the

issues related to traversal of NAT, V4-V6 gateways, and firewalls

need some serious consideration.

 

The choice of UDP-Lite as the transport for IPv6 was based on

performance reasons.  Most ACs today do the 802.3-to-802.11

conversion and encapsulation in hardware, and in our discussions

the consensus was that requiring checksum computation in hardware

would be expensive. However, it seems that the CAPWAP protocol

has serious issues related to traversal of NATs and firewalls

when using IPv6 since such boxes don't typically support UDP-Lite.

 

This means that we should make UDP the mandatory transport for

IPv6.  We could still allow for UDP-Lite when there are translation

gateways and firewalls present.

 

Thoughts/comments ?

 

Abhijit

 

p.s. Proposed text for updating Section 3 is provided below.

Other minor changes will be needed to remove mention of UDP-Lite in the

document.

 

 

----------------------  PROPOSED TEXT ----------------------------------

3.  CAPWAP Transport

 

   Communication between a WTP and an AC is established according to the
   standard UDP client/server model.  The CAPWAP protocol uses UDP as the

   transport protocol for both IPv4 and IPv6.  This section describes how

   the CAPWAP protocol is carried over IP and UDP protocols.

 

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 a CAPWAP session is initiated by the WTP (client) to the well-
   known UDP port of the AC (server), the use of UDP is a logical
   choice.  For IPv4, the UDP checksum field in CAPWAP packets MUST be

   set to zero.

 

   CAPWAP protocol control packets sent from the WTP to the AC use the
   CAPWAP control channel, as defined in Section 1.4.  The CAPWAP
   control port at the AC is the well known UDP port [to be IANA
   assigned].  The CAPWAP control port at the WTP can be any port
   selected by the WTP.

 

   CAPWAP protocol data packets sent from the WTP to the AC use the
   CAPWAP data channel, as defined in Section 1.4.  The CAPWAP data port
   at the AC is the well known UDP port [to be IANA assigned].  The
   CAPWAP data port at the WTP can be any port selected by the WTP.

<DELETE Section 3.2>