Re: A question of small MTUs

On Wed, 13 Nov 2002, William Ivancic wrote:

> I'm not sure about the largest or smallest MTU size, but I thought it may 
> be appropriate to note some behaviors and problems we were having with MTU 
> discovery over mobile networks using mobile-IPv4 double tunnels and 
> encryption.   The mobile-IPv4 mobile networking we are using applies double 
> tunnels from the home agent to the foreign agent when foreign agent service 
> is used.   Adding encryption on top of that hides MTU discovery.  To add to 
> the problem, somewhere the don't fragment bit is being set - perhaps in 
> some applications or at some Web servers.  Thus, we manually have to set 
> the Max MTU in the hosts on the mobile LAN or set the minimum acceptable 
> MTU size at the last visible interface to the mobile LAN.

I'm a little curious to know how you think this is supposed to work.  If you 
are using any advanced TCP features (e.g. PAWS RFC1323) or IPv6 then DF becomes 
mandatory.

I think that our algorithm will indeed solve your problem for the TCP based
applications, although I can't tell from your message what is the MTU of the
inner most tunnel. It sounds like 1500 - 4*tunnel_overhead.  Is that correct?  
What was the actual size?

Thanks,
--MM--
----------------------------------------------
Matt Mathis <[email protected]>    W:412.268.3319
http://www.psc.edu/~mathis      H:412.654.7529
----------------------------------------------


_______________________________________________
pilc mailing list
[email protected]
https://www1.ietf.org/mailman/listinfo/pilc
http://www.ietf.org/html.charters/pilc-charter.html
http://pilc.grc.nasa.gov/