[c-nsp] Show system jumbomtu

[Sukumar Subburayan]

On Fri, 30 Mar 2007, James Slepicka wrote:

> >>There is no need to touch 'vlan MTU' in the vlan config mode to support
> Jumbo frames.
> I've always wondered about this.  If this isn't required for jumbo frame
> support, what is its purpose?
>

It has been a legacy since the original Cat5k days where vlan mtu was 
needed for supporting TokenRing CRFs etc..

We probably never cleaned it up.

sukumar

> Sukumar Subburayan wrote:
>
>  Global System MTU can be used for dropping packets on the 
> egress.
> 
> For eg, if the 'system jumbomtu.. ' is set at 5000 byte,s this will
> make all switchports with 'mtu 9216' to drop packets above 5000 bytes on 
> the egress, regardless of the individual port mtu configuration.
> 
> L2/L3 physical Interface MTU (mtu <mtu-size>) is used to enable jumbo 
> frame support on the physical interfaces for L2 or L3.
> 
> SVI MTU again can be used to enable L3 Jumbo frame support for that 
> Switch Virtual Interface (SVI).
> 
> There is no need to touch 'vlan MTU' in the vlan config mode to support 
> Jumbo frames.
> 
> When you enable L3 Jumbo frame support on L3 ports (L3 physical port or 
> SVI), it automatically adjusts 'ip mtu..' . The reverse is not true.
> 
> I don't know about MPLS MTU stuff. Someone else can chime in.
> 
> How you want to use all this depends on what you want to do.
> 
> 
> sukumar
> 
> On Fri, 30 Mar 2007, Alaerte.Vidali at nokia.com wrote:
>
> 
>
>  Thank you.
> 
> Would you indicate good documentation public available that explains if
> when using system MTU it is still necessary use interface MTU?
> (or not)
> 
> And shows the relation between:
> Vlan MTU
> System MTU
> MPLS MTU
> Interface MTU
> 
> I read documents I found in Cisco page, and applied it on 7600. The
> result I got is that only system MTU was not enough. It was necessary
> configure interface MTU.
> 
> 
> Regards,
> Alaerte
> 
> -----Original Message-----
> From: ext Sukumar Subburayan [mailto:sukumars at cisco.com]
> Sent: Friday, March 30, 2007 3:27 PM
> To: Vidali Alaerte (Nokia-NET/RioDeJaneiro)
> Cc: cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] Show system jumbomtu
> 
> We had supported 'show system mtu' cli only on the cat4k.
> 
> On the 6k, since the configured system MTU can be viewed in the running
> config, it command to show the value was not added.
> 
> we never got to implement 'show system jumbomtu'.
> 
> Please refer to CSCdy28580
> 
> sukumar
> 
> 
> 
> 
> On Fri, 30 Mar 2007, Alaerte.Vidali at nokia.com wrote:
>
> 
>
>  Do you know if there is any hidden issue with this command?
> 
> I tried it in 2 IOS versions it was supposed to work, but no support.
> 
> Version 12.2(33)SRA1
> 
> OSR-1#show system ?
> % Unrecognized command
> OSR-1#show system
> 
> Version 12.2(17d)SXB7
> OSR-2#sh system?
> % Unrecognized command
> OSR-2#sh system
> 
> 
> 
> Tks,
> Alaerte
> 
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