[c-nsp] Are Nexus and per-interface or FEX MTU settings possible?

[Andrew Jones]

PMTUD should take care of the rest... 

Andrew Jones


-----Original Message-----
From: Conkel, Joshua [mailto:ConkelJ at WEMS-LLC.com] 
Sent: Saturday, 22 September 2012 10:47 AM
To: Andrew Jones
Cc: cisco-nsp at puck.nether.net
Subject: RE: Are Nexus and per-interface or FEX MTU settings possible?

Actually, I just installed a 10G LR fiber optic module in each of them in order to connect to the 5Ks.

I was sure to add the spanning-tree port type edge trunk command on the Nexus so I didn't risk ISSU support.

The way I see it, we should be able to keep this working by making sure no hosts go beyond the MTU limit on the smallest switch, since frames don't magically consolidate themselves. :)

The iSCSI jumbos have their own switch linked separately in a stack for the jumbo support.

Thanks!
----- Original Message -----
From:Andrew Jones <Andrew.Jones at alphawest.com.au> To:"Conkel, Joshua" <ConkelJ at WEMS-LLC.com>, "cisco-nsp at puck.nether.net" <cisco-nsp at puck.nether.net>
Sent:9/21/2012 8:39 PM
Subject:RE: Are Nexus and per-interface or FEX MTU settings possible?



Im assuming your 3560 has gigabit ports to connet the 5ks?

Then you can do jumbo frames on those interfaces, as per the following from cisco.com http://www.cisco.com/en/US/products/hw/switches/ps700/products_configuration_example09186a008010edab.shtml#c3

You will need to reboot the switch for this to take effect.

Andrew Jones


-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Conkel, Joshua
Sent: Thursday, 20 September 2012 12:57 PM
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] Are Nexus and per-interface or FEX MTU settings possible?

We just bought a bundle of 2x 5548Ps and 20x 2248s in order to converge our data and storage networks in our new datacenter. After carefully reading the configuration limitations document and designing around the limitations for our migration, we pulled the trigger and bought the material. The document that I used as prep work for the actual deployment was Data Center Access Design with Cisco Nexus 5000 Series Switches and 2000 Series Fabric Extenders and Virtual PortChannels. I planned on being able to hook the Nexus up to our distribution switches and standalone iSCSI network for the migration process and to provide L3 services (because of the limitations with using the L3 routing modules)

Now on to our issue:
The document states that you can configure per-interface MTU size. Our data network distribution switches are 3560s and run the standard MTU size of 1500. Our iSCSI network, on the other hand, use jumbo frames with a MTU of 9000. After trying the steps outlined in the document, I have only been able to set the MTU globally on the Nexus to jumbo or non-jumbo. After contacting TAC, they have initially confirmed that the MTU qos policy can only be applied at the system level, not per interface.

So, any ideas other than not converging our networks and buying a standalone 4900 or 3750x series pair for our iSCSI network? Sorry if it's wordy, but this is the content I gave to TAC as well.
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