Subject: Re: [Capwap] Control channel packet classification

From: "Pat Calhoun (pacalhou)" <[email-masked]>
Date: Mon, 25 Sep 2006 12:25:48 -0700

Hasan,
 
This issue should be clarified in the spec, so I have created issue 224
to track it.

Pat Calhoun
CTO, Wireless Networking Business Unit
Cisco Systems

________________________________

	From: Hasan Raza [mailto:[email-masked]] 
	Sent: Tuesday, August 22, 2006 2:06 AM
	To: [email-masked]
	Subject: [Capwap] Control channel packet classification

	Hi,
	
	I have a basic question regarding the classification of packets
exchanged over
	control channel. It is stated in the draft that AC in Idle state
can receive
	Discovery as well as DTLS clientHello (+other dtls handshake)
packets. The
	clientHello packets are delivered to the SSL layer and Discovery
packets are
	consumed by the CAPWAP. Question is how? The draft assumes some
magic
	way of doing it. Since both of the packets are in plain, and are
received on
	a single udp port, which state/policy/field classifies such
packets from one
	another? Theoretically speaking, WTP can send a discovery packet
which is
	also a valid clientHello packet! Now AC would respond with a
discovery
	response or a clientHello reponse?

	In thread
http://lists.frascone.com/pipermail/capwap/msg03035.html, Pat talks
about
	the negotiated policy for the appropriate treatment of the
received packets. That may
	mean, if the AC is in join onwards state, it can be assumed that
AC will only receive
	encrypted packets. Though this policy can work, but there would
be exceptions in
	which WTP dies and comes back with a discovery packet. AC still
being in join+
	state, the received packets will be delivered to the SSL layer.
Assumptions can be
	made here that SSL would discard non-dtls packets and with
timeouts in picture, WTP
	and AC would eventually reach a consensus. But is this ok to
assume?
	
	In the same thread, Perkins suggested the mux header approach
for control channel,
	but it was not acknowledged? Is there some other hidden
mechanism for the
	classification? Or there is some basic point which I miss here?

	Thanks
	Hasan

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