MTU size on vlans

[pipsadmin]

Is it possible to specify MTU size on specific vlans? A manufacturer of network storage recommends setting up MTU size to 2250 on the replication vlan.

Thanks

[Joseph W. Doherty]

"Is it possible to specify MTU size on specific vlans?"

Depends on the hardware. If we're talking Ethernet, many newer switches support "jumbo" frames, usually up to about 9K. For intensive data transfers, such as replication, the larger frames use more of the bandwidth for payload, especially at higher bandwidths (e.g. gig).

Unsure why the vendor recommended 2250, normally I would expect usage of the largest MTU that can be supported end-to-end. Perhaps, the network storage device's maximum MTU is 2250.

[Amit Singh]

Nope its not possible on the specific vlans. You can only set it system wide for all the ports.

-amit singh

[Joseph W. Doherty]

Excellent point, although, and correct me if I'm mistaken, there should be little risk to enable jumbo frames globally if supported by the switch as other devices using "standard" size frames would continue to function normally. (This is also assuming any network devices along a path, end-to-end, where jumbos might be used are all so configured.)

[pipsadmin]

The switch in question are 6513's and 6509's with Dual SUP720's

[pipsadmin]

So is it safe to enable jumbo frames on CORE 6500's whithout affecting the network when enabling?

What is the command to enable Jumbo frame and/or see if Jumbo frames are already enabled in the switch?

[pipsadmin]

Also, from the documentation, it does not state if the WS-X6148A-GE-TX support jumbo frames or not...?!?

[Joseph W. Doherty]

Set table 5 in: http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/product_data_sheet0900aecd8017376e.html which notes the WS-X6148A-GE-TX supports jumbo frames up to 9216.

[pipsadmin]

so there should not be any issue enabling jumbo frames on the switch then?

[Joseph W. Doherty]

I don't have first hand experience with your particular hardware to guarantee you won't. However, I think it a good sign that there hasn't been a post to the contrary.

With regard to your earlier posts on "how to", the software guides and reference guides for your software/hardware would have the information, but this might also help: http://www.cisco.com/en/US/products/hw/switches/ps700/products_configuration_example09186a008010edab.shtml#c1

[tholmes]

Hi

I saw your post and hope you can help.

I've got a 6513/SUP720 and gig line cards, all the gigabit interfaces are set to MTU 9216 but the SVI VLAN interfaces are not, would this cause an issue, there are a few input drops on interfaces and sometimes the network performance is reported at be slow.

Any help appreciated

Regards Tony

[md farook]

MTU is for physical device not for virtually configured object like for VLAN.If i am right then 1500 is most preferable vlaue which could be used by all vendors.

[bilousand]

The link should clear everything up :)

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/intrface.html#wp1041111

[tholmes]

Hi thanks for the reply

Yes - I read that section of CCO

>VLAN Interfaces

You can configure a different MTU size on each Layer 3 VLAN interface.

>Configuring a nondefault MTU size on a VLAN interface limits traffic to the nondefault MTU size. (THIS IS THE BIT THAT WORRIES ME)

(does that mean every other size is dropped, probably not so what do they mean 'LIMITS'?)

You can configure the MTU size on VLAN interfaces to support jumbo frames.

Cheers Tony

[bilousand]

The fact you CAN configure MTU size on SVI is probably misleading. It obviously won't affect ANY L2 traffic inside VLAN.

"Limits" means "up to and including".