Capwap Mailing List: Re: UDP-Lite as optional transport for CAPWAP

[Sudhanshu (sudhanshu.ietf]

I don't think we need to care for the NAT transport as such. CAPWAP is an
application to UDP (and now UDP-lite) and we can leave it there. CAPWAP
provide the consideration (guidelines) on how to work over NAT, which is
different from NAT transport.

My 2cents. Also there is no reason for us to specify UDP is mandatory for
IPv4 and UDP-lite for IPv6. Although, it would be the most likely case.

UDP-lite no where mention that it is for IPv6 only. And if some deployments
don't want to trust the media/link, it should be OK to use UDP over IPv6.
CAPWAP does not need to limit itself.

_Suds


-----Original Message-----
From: Pat Calhoun (pacalhou) [mailto:pcalhoun [at] cisco.com] 
Sent: Wednesday, March 14, 2007 3:02 PM
To: Puneet Agarwal; David Melman; capwap [at] frascone.com
Subject: Re: [Capwap] UDP-Lite as optional transport for CAPWAP

That may be an issue for IPv6, but note that NATs are supposed to go
away with the new address space... I don't have lots of visibility into
this space though.

Pat Calhoun
CTO, Wireless Networking Business Unit
Cisco Systems

 

> -----Original Message-----
> From: Puneet Agarwal [mailto:pagarwal [at] broadcom.com] 
> Sent: Wednesday, March 14, 2007 2:45 PM
> To: Pat Calhoun (pacalhou); David Melman; capwap [at] frascone.com
> Subject: RE: [Capwap] UDP-Lite as optional transport for CAPWAP
> 
> Hi Pat,
> 
> One of the goals of capwap was to go easily through 
> firewalls/nats. Is UDP-lite supported by the existing 
> nat/firewalls (since the nat will have to play around with 
> the checksum which includes the ip psuedo-hdr)?
> 
> Thanks.
> 
> -Puneet
> 
> -----Original Message-----
> From: Pat Calhoun (pacalhou) [mailto:pcalhoun [at] cisco.com]
> Sent: Tuesday, March 13, 2007 12:59 PM
> To: Pat Calhoun (pacalhou); David Melman; capwap [at] frascone.com
> Subject: Re: [Capwap] UDP-Lite as optional transport for CAPWAP
> 
> Let me try again. UDP-Lite should be mandatory when run over 
> IPv6. UDP should continue to be mandatory when run over IPv4.
> 
> Pat Calhoun
> CTO, Wireless Networking Business Unit
> Cisco Systems
> 
>  
> 
> > -----Original Message-----
> > From: Pat Calhoun (pacalhou)
> > Sent: Tuesday, March 13, 2007 7:40 AM
> > To: David Melman; capwap [at] frascone.com
> > Subject: Re: [Capwap] UDP-Lite as optional transport for CAPWAP
> > 
> > I completely agree with this request, and believe that if we want 
> > CAPWAP to work over v6, the change is needed in this version of the 
> > protocol, as requiring the UDP checksum be computed on each 
> IPv6/UDP 
> > CAPWAP packet would have a dramatic performance impact. I do not 
> > believe the feature should be optional for v4 networks.
> > 
> > I have created issue 249. It is currently marked as a wish, 
> but as per
> 
> > my above statement, I believe we should categorize it as a bug.
> > 
> > Pat Calhoun
> > CTO, Wireless Networking Business Unit Cisco Systems
> > 
> >  
> > 
> > > -----Original Message-----
> > > From: David Melman [mailto:davidme [at] marvell.com]
> > > Sent: Tuesday, March 13, 2007 1:29 AM
> > > To: capwap [at] frascone.com
> > > Subject: [Capwap] UDP-Lite as optional transport for CAPWAP
> > > 
> > > Hi.
> > > 
> > > In supporting CAPWAP-over-UDP-IPv6, I'm concerned about 
> the cost & 
> > > performance overhead of supporting a full UDP checksum over
> > the entire
> > > UDP payload.
> > > 
> > > While UDP over IPv4 allows the UDP checksum to be set 0
> > indicating the
> > > UDP checksum is not calculated, UDP over IPv6 requires the
> > UDP header
> > > to contain a checksum which covers the UDP pseudo header
> > and the UDP
> > > payload (per RFC 2460).
> > > Calculating the checksum over the full data payload adds
> > significant
> > > cost and performance overhead, both to the AC switch (typically 
> > > implemented in hardware) and the WTP (typically implemented in 
> > > software).
> > > 
> > > I propose to allow CAPWAP over UDP-Lite (RFC 3828) as an optional 
> > > transport to UDP, particularly for the CAPWAP data channel
> > which would
> > > be impacted the most by the requirement to calculate the
> > UDP checksum
> > > over the entire payload.
> > > 
> > > The UDP-Lite header is identical to the UDP header, except
> > for the UDP
> > > Length field which is replaced with the Checksum Coverage
> > field. The
> > > Checksum Coverage field indicates the number of octets,
> > counting from
> > > the first octet of the UDP-Lite header, that are covered by the 
> > > checksum. To minimize the performance impact, the UDP Checksum 
> > > Coverage is set to the minimal value of 8, which limits the UDP 
> > > checksum to cover just the UDP pseudo-header, excluding the UDP 
> > > payload.  (Note that the UDP Length field is not required,
> > as it can
> > > easily be calculated by subtracting 8 (UDP-Lite header
> > > length) from the IP Length field.)
> > > 
> > > UDP-Lite (RFC2460) is widely available in IPv6 stacks and
> > in all the
> > > common operating systems we surveyed.
> > > 
> > > I believe this change would have minimal impact to the
> > CAPWAP protocol
> > > and has significant value to both hardware and software 
> > > implementations.
> > > 
> > > Regards,
> > > David
> > >  
> > > __________________________________________
> > > 
> > > David Melman
> > > Architecture group - Marvell
> > > Email - DavidMe [at] marvell.com
> > > 
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