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Increasing MTU size (Jumbo frames)

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Achillesx

Achillesx

IS-IT--Management
Aug 18, 2005
31
GB
Hi all,

I was considering increasing the MTU size on our backup server to maybe 6000 (from its default of 1500) to try to increase throughput.

I was wondering what effect (on the rest of the network) increasing the MTU size on the switch ports used our the backup server (used to connect to its targets) would have.

All our client PCs use 1500, would this affect them? They dont generally connect directly to the backup server.

If I set the MTU size on our switches to 6000, would everything else set to 1500 work as normal (at 1500)?

If I set our file server (FAS270) to 6000 would our clients still connect at 1500 (as that what their NICs are set to)?

Many thanks,

NP
 
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You'll have all kinds of problems if devices in te path to the server have MTU set lower than 6000...that just means it won't fragment until 6000 bytes...try an extended ping and turn the df bit to on, with sweep ranges, and when you error out (path between switch and server), then it shows what the mtu should be set to, that it can handle.

Burt
 
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Thanks for that..
So if I ensure that all Switches in the path to the server are set to support 6000, would our clients be ok connecting at 1500?
I dont want to increase our client PC's mtu - just servers that our backup server tries to connect to (all on our LAN).

Cheers

NP


 
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The switchports that the servers connect to should be okay to set mtu to 6000, but the switchports that pc's with 1500 mtu should be set to 1500 mtu.

Burt
 
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The query I have is whether the PC's set to 1500mtu connected to ports at 1500mtu will have problems when they try to connect to our filer (which will have an mtu size of 6000 on a port set to 6000)..

Cheers

NP
 
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I believe you will see problems when the filer tries to pass 6000 byte packets to the pc's when they're expecting 1500 byte packets (you should get a destination unreachable), but I don't think there will be problems if the pc's send 1500 byte packets to the server. That's a new one on me, so I'm just taking a guess...try it.

Burt
 
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I'll try it with a few test laptops to see what happens - off our main network..

Cheers


NP
 
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