Capwap Mailing List: Re: Issue #3: MTU Discovery Requirement

[Smitha Smitha (ssmitha) (ssmitha]

Margaret,

Could we reserve packet types to do MTU discovery? We can then use that
packet type say "path mtu request" and "path mtu response" along with
the path MTU payload described in the draft. 

Thanks
smitha

-----Original Message-----
From: Margaret Wasserman [mailto:margaret [at] thingmagic.com] 
Sent: Wednesday, July 18, 2007 8:06 PM
To: capwap
Subject: [Capwap] Issue #3: MTU Discovery Requirement

Lars Eggert and Magnus Westerlund raised an issue with the WG regarding
the lack of a Path MTU Discovery mechanism in CAPWAP.  We can either
introduce this type of mechanism (to avoid fragmentation) or we can
limit our message size to the minimum MTU (512 bytes for IPv4, 1280
bytes for IPv6).

 > Specifically, I remember a discussion that  > concluded that CAPWAP
would need to have a mechanism to decide what MTU  > to use and would
need to default to a minimum MTU size (512
bytes?) when
 > no other information was available, in order to avoid fragmentation.
Is  > that still a concern regarding the CAPWAP protocol?  If so, do you
(or  > Dave or Lars) have any advice about how we might address it?

Yes, you likely need to have a MTU discovery mechanism to be avoid
needing to use very conservative packet sizes. But there should be
possible to implement something like the MTU discovery method described
in RFC 4821 in the CAPWAP protocol.
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