MTU Thoughts

Okay, here in my lab I have an MTU issue that I am facing.

I need to know if setting the "system mtu routing 9000" on my Cisco switch will allow jumbo frames in the network. Becuase currently it is working but not working everywhere. or to better put it they are not working when communicating with one VMware server. it is very intermittent. from one place in the network it will work and from the other, it won't.

so ping from the VMware switch to my storage device. I get the following.

""ping size 1500
 Pinging with 1500 bytes of data:
---- PING statistics----
4 packets transmitted, 0 packets received, 100% packet loss
round-trip (msec) min/avg/max = <10/<10/<10""

But ping with 1400 will work just fine. Now if I go to the storage device and ping the same way it working fine, pinging the switch works with no problems.

Any thoughts on this.
Jordan TaylorNetwork EngineerAsked:
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Travis MartinezStorage EngineerCommented:
If you have an end point device set for an MTU size of 9000 then everything in the chain has to be set that way too.  You can always go lower but you can't go higher.
Jordan TaylorNetwork EngineerAuthor Commented:
So If my storage device is set at 9000, and my pc is not they should not be communicating at 9000?
Travis MartinezStorage EngineerCommented:
That's correct.  If one end point, the "PC", is set for 1500 and talking to a storage device that's set at 9000 the connection shouldn't work.  That's what I believe anyway's.  I would get a second opinion from others but the systems are trying to communicate in different packet sizes.
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Jordan TaylorNetwork EngineerAuthor Commented:
And correct me if I am wrong if they are talking 1500 and one PC is at 9000 and the other is at 1500 this should work?
Travis MartinezStorage EngineerCommented:
The 1500 talking to the 9000 should work but the 9000 to the 1500 shouldn't.  I'm currently working storage on a NetApp and have had issues with the MTU sizes before.  If you want 9000 then everything in the path should be set that way.

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Jordan TaylorNetwork EngineerAuthor Commented:
Yeah, our storage provider is saying to have Jumbo frames enable in that line of communication. Okay sounds like the only way to tell what is really going on is to have it on everything in the path to be set that way.

and see if that makes a difference.

At the moment the storage device(9000MTU) can talk to the Vmware Switch(1400MTU) at 9000 but the other way around this does not work.

Thanks for the advice.
Jordan TaylorNetwork EngineerAuthor Commented:
Going to test. should resolve these issues.
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