[c-nsp] MTU Mismatch

[Jason LeBlanc]

In a typical 3 tiered infrastructure I would assume it must be commonplace practice to house some vlans with Jumbo frames support.  We have 2 options currently connecting devices from access to distribution.

Access		Distribution
3550    <->	6500
4500    <->	6500

We have customers segmented on L2/L3 vlans requesting Jumbo frames in various environments.  Some request separate hardware altogether like for Oracle RAC.  How have you guys seen this implemented?

Cheers,

// LeBlanc


On Dec 28, 2009, at 1:40 PM, Mack McBride wrote:

> If jumbo frames are enabled on edge ports but not in the middle there can be issues.
> Layer 2 will not fragment packets and layer 3 will fragment in software.
> It is better to have jumbos in the middle but not on the edges where there will not be issues.  Basically the smallest packet size should be at the edge and the core
> should have a larger size than the edge.
> 
> LR Mack McBride
> Network Architect
> Viawest, Inc.
> 
> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Jason LeBlanc
> Sent: Monday, December 28, 2009 10:09 AM
> To: Marko Milivojevic
> Cc: cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] MTU Mismatch
> 
>> From a routing perspective this makes sense.  Will there be any adverse effects if the Jumbo frames is bumped up anywhere in the chain?  Meaning L2 vs. the L3 Routing.  I believe thats where the MTU path discovery comes into play correct?  Sorry to add to this but while we were on the subject I figured I would ask :)  We want to use jumbo frames in a few environments but not at the cost of anything in the path.
> 
> Cheers,
> 
> // LeBlanc
> 
> On Dec 28, 2009, at 9:09 AM, Marko Milivojevic wrote:
> 
>> On Mon, Dec 28, 2009 at 16:00, Mohammad Khalil <eng_mssk at hotmail.com> wrote:
>>> 
>>> i have checked the mtu on 3750
>>> sh system mtu
>>> 
>>> System MTU size is 1500 bytes
>>> System Jumbo MTU size is 1512 bytes
>>> Routing MTU size is 1500 bytes
>>> 
>>> but there is no such command on the 6523
>> 
>> Different beast, but at least you get the explanation. As far as
>> routing processes go, MTU on 3750 is 1500. On 6500 you can set it per
>> interface (depending on the LC).
>> 
>> --
>> Marko Milivojevic - CCIE #18427
>> Senior Technical Instructor - IPexpert
>> 
>> Mailto: markom at ipexpert.com
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