From: ccie2be (ccie2be@nyc.rr.com)
Date: Wed Jun 15 2005 - 15:16:49 GMT-3
Hey John,
I don't really know the answer but I know how you can find out.
Set different values for the system mtu and interface mtu and do pings of
different sizes.
Turn on icmp debugging and don't forget to turn off, ip route-cache, log the
output and see what happens.
HTH, Tim
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of John
Matus
Sent: Wednesday, June 15, 2005 1:24 PM
To: ccie2be@nyc.rr.com; ccielab@groupstudy.com
Subject: RE: system mtu
so then, if the system mtu is set at a value less than the interface mtu,
the the packet will not be fragmented?...perhaps dropped?
>From: "ccie2be" <ccie2be@nyc.rr.com>
>To: "'John Matus'" <john_matus@hotmail.com>, <ccielab@groupstudy.com>
>Subject: RE: system mtu
>Date: Wed, 15 Jun 2005 08:04:47 -0400
>
>John,
>
>Suppose a router had a bunch of serial interfaces with an MTU of 10,000 and
>an ethernet interface with an MTU of 1500.
>
>And, let's say the system MTU was set to 10,000 and the eth interface MTU
>was set to 1500.
>
>Now, the router wants to send a packet of size 3000 out the ethernet
>interface.
>
>Based on the system MTU, no fragmentation is needed. What does the router
>do?
>
>Since it's not possible to send a 3000 byte packet out an ethernet
>interface
>with a max MTU of 1500, I would say the router will fragment that packet.
>
>HTH, Tim
>
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
>John
>Matus
>Sent: Wednesday, June 15, 2005 12:32 AM
>To: ccielab@groupstudy.com
>Subject: system mtu
>
>question regarding mtu on an interface and globally and how the 2 interact
>with each other...
>i think i know part of it but i don't know which direction it works..
>
>is it - if the interface exceeds it's own mtu, then it will fragment
>packets in accordance with the system mtu? or is it the other way
>around....
>or....
>
>is the global mtu the default for all interfaces and the interface mtu just
>overrides the global setting?
>
>TIA
>
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