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Re: [Isis-wg] [rbridge] Why is MTU discovery important?

No, Vishwas -- merely stating the MTU is not sufficient, because there could
be components between two RBridges (like, for instance, bridges), that wind up causing a big packet not to get through. So to really test the MTU requires a padded packet, (but it need not be (and MUST NOT be, for TRILL) the same, simultaneous mechanism as finding neighbors, such as layer 3 IS-IS which does not see neighbors that can't 
be reached using the largest packets.)

Radia

Vishwas Manral wrote:

Hi,

Though the MTU padding of Hello's is one way of getting the MTU right in all
the machines, a simpler and more efficient way would be to actually exchange
MTU values in a TLV.

The reason padding of Hellos was done in a layer 3 network, instead of a TLV
was because if between 2 - Layer 3 peers there was a switched network (not
just a single link), and the MTU in the links somewhere in between was
lesser, there would be no way to figure that out. 
For trying to work IS-IS for layer 2 the reason no longer holds good.
Thanks, 
Vishwas

-----Original Message-----
From: isis-wg-bounces at ietf.org [mailto:isis-wg-bounces at ietf.org] On Behalf
Of Tony Li
Sent: Thursday, April 09, 2009 9:55 PM
To: Don Fedyk
Cc: TRILL/RBridge Working Group; Radia Perlman; isis-wg at ietf.org; Dinesh G
Dutt
Subject: Re: [Isis-wg] [rbridge] Why is MTU discovery important?

Don Fedyk wrote:
I have a different interpretation. I think you just broke an IS-IS safeguard by not padding Hellos. 


+1

Tony