[cisco-bba] 'mtu' versus 'ip mtu'

Frank Bulk frnkblk at iname.com
Tue Dec 2 14:13:35 EST 2008



Thanks for that reference.  There's a lot of talk in there about MPLS MTU,
not so much IP MTU.  One sentence jumped out at me:


"A best practice is to set the interface MTU of the core-facing interface to
a value greater than either the IP MTU or interface MTU of the edge-facing


Since my interface MTU (mtu 1492), is not greater than the IP MTU (ip mtu
1492), doesn't that suggest I should be dropping the value of my ip mtu to
comply with this best practice?




From: arievayner at gmail.com [mailto:arievayner at gmail.com] On Behalf Of Arie
Sent: Tuesday, December 02, 2008 11:24 AM
To: Frank Bulk
Cc: cisco-bba at puck.nether.net
Subject: Re: [cisco-bba] 'mtu' versus 'ip mtu'



This is a good reference:


On Tue, Dec 2, 2008 at 11:14 AM, Frank Bulk <frnkblk at iname.com> wrote:

I 'upgraded' from 12.4(19b) to 12.2(SB11)31 this morning and rancid is
showing me that IOS automatically added 'ip mtu 1492' to my interface.

I already had the following in there:
  mtu 1492
  ip tcp adjust-mss 1452
  ppp mtu adaptive

Do I need to set my ip mtu to some other value?


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