Catalyst 3750X jumbo frames configuration

[jaime madruga]

                   I need some guidance configuring jumbo frames on my enviroment. We are building a vmware enviroment with an ISCSI storage appliance

we have been advice to configure the ISCSI traffic for MTU 9000 - Jumbo frames. Our infrastructure is using Catalyst 3750X switches and it seems that Jumbo frames can only be configured at the global level. Im concern that by enabling Jumbo frames globall any other resouces using MTU 1500 will be impacted. By the way is on stack of 6 C3750X switches. Basically the only request is to have the ISCSI traffic on Jumbo frames and its own vlan.

[Marvin Rhoads]

Sorry but it's all or nothing on the 3750X.

The ability to fine tune features like that at the interface level is an example of the differentiators between accees switches like the 3750X and a data center switch like the Nexus line.

[jaime madruga]

Thanks, this is a 48 port switch if jumbo frame is enabled and other resources are configured locally to transmit using MTU 1500, I would assume this traffic will be impacted?

[Marvin Rhoads]

Configuring a switch to support jumbo frames only affects how the switch accepts the frames from the end stations - i.e.  giving enough buffer space for frames larger than the default 1500 byte system MTU.

It does not affect whatever local MTU is set on end systems. So if the non-iSCSI host are sending out frames with a non-jumbo MTU today, that will not change just because and upstream switch or switches support a larger MTU size.

The only potential impact on them is that if the switch (or stack) is VERY heavily utilized, having to reserve more buffers for the jumbo MTU would theoretically use some resources that might allow you get get that last few percent of throughput. I'd say that's a "corner case" though and not likely to be seen in most installations.

It would be something to watch though in the case of an access switch being used as a data center switch. The 3750X is pretty capable but it's not a full non-blocking architecture.

[jaime madruga]

Great, thanks for your help.

[Marvin Rhoads · Accepted solution]

You're welcome. Please rate helpful replies and mark your question as answered if it is.