EFFECTS OF CONFIGURING SYSTEM JUMBO FRAME

[kehinde olugotun]

Hi, we have a 6506 switch which had a default setting of mtu 1500.

Now we have a client who is requesting that we set the jumbo frame to 9216.

I configured      # int fx/x

                      # mtu 9216

This did not solve the problem as they said they are still not able to get the desired mtu value.

Am thinking of configuring a ssytem jumbomtu 9216 on the switch

What are the implication?

Would there be any performance issue after initiating this command?

Would it solve the current issue?

Regards,

Kenny

[JohnTylerPearce]

If you issue that global configuration command, it is very possible to run into problems. That command will set the mtu to the max of 9216 for all ports, so if you have a port going to your WAN provider, etc, it will cause frames to be fragmented on their end, since most likely the other port will be 1500. So take 9216/1500, and could have lots of issues with CPU performance. I've had friends that have had that happen to them.

I haven't set the MTU value on a 6500, but I have done it on a 3750/2960-s, and I had to reboot the switch. If you run the command 'show system mtu', it will say something like "won't take place until next reboot'.

Is there a specific reason, the client needs to have this value set on the port? I would think going to the interface, and putting in the mtu command would work. Did you verify that the MTU value took on the interface?

[pille1234]

Be aware that all interfaces between source and destination interface need to be configured for jumbo frames. That includes the layer-3 Vlan-interfaces as well.

[Joseph W. Doherty]

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Posting

I configured      # int fx/x
                      # mtu 9216
This did not solve the problem as they said they are still not able to get the desired mtu value.

You normally need to insure jumbo is enabled end-to-end.

Am thinking of configuring a ssytem jumbomtu 9216 on the switch
What are the implication?

Hmm, is that supported on the 6500?  On 6500s, MTU can be set per interface.  Not all line cards support jumbo.  If a system wide jumbo setting is supported, it might enable jumbo for all interfaces that can support it.  Biggest implication is an interface might transmit a jumbo to a device incapable of receiving it.

Would there be any performance issue after initiating this command?

To the 6500?  Shouldn't be.  Existing hosts?  May enhance or decrease their performance, or break transfers.

Would it solve the current issue?

Not enough information to say.

[kehinde olugotun]

Thanks so much for the information. After issuing

S(conf)# int g3/23

               mtu 9216

I also did

S(conf)# system jumbomtu 9216          (didnt ask for a system restart and not much difference as Joseph pointed out)

I issued the show vlan mtu

6506#     sh vlan mtu

VLAN    SVI_MTU    MinMTU(port)   MaxMTU(port)  MTU_Mismatch

---- ------------- -------------  ------------  ------------

113       1500          1500                      1500           No

114       1500          1500                      1500           No

115        1500          9216                     9216           No

116       1500          9216                      9216           No

6506#     sh int mtu

Port       Name               MTU

Gi3/23     V_TRUNK      9216

The design scenario we have is V switch connects to our 6506. Our 6506 connects to a fiber equipment (Optical Line Terminal). The OLT connects to an ONU which is deployed to the Client.

The Client mentioned they oberved a considerable improvement but they still cant get to the desired mtu of 9216

Regards,

Kehinde