Jumbo Frames, MAX MTU

Posted on 2012-09-18
Last Modified: 2012-09-18
I want to enable jumbo frames on my NAS and server.  My switch, netgear GS748T, supports it as well as the NAS, netgear readynas 1100, and server NIC i believe.  The server nic is a Broadcom BCM5708C NetXtreme II.  I set Jumbo MTU to 7500 on the server.  I set the max. frame size on the ports on the switch to 7500.  I turned on jumbo frames on the netgear readynas 1100.

When I ping from the server to the nas with ping -f -l i get times out on anything above 1476.
When I ping from teh server to the switch i get time outs on anything above 1472.
When I ping from the server i get packet needs to be fragmented message on anything 1492.

I guess the server nic is not handling the jumbo frames then?
is pinging a sufficient test for testing the server handling jumbo frames?
do i need to reboot when i make these changes?
Question by:Grolff
    LVL 5

    Accepted Solution

    Your NAS may not have enabled the new setting unless you've restarted it.

    Pinging local is not adequate a test.

    Another thing to pay attention to....the cabling from the NAS to the server, or NAS to a switch, and then the server --- Make sure you're using good cables.

    I learned that just because a cable is listed as CAT5, it does NOT properly support full 1GB traffic ---  Moving to CAT 6 cables --- instantly solved the limits....

    As I understand it, CAT 5 will support 1gb, but not in duplex....  I'll leave that argument for others....   But, the point I'm going for --- if you're going to play with frame sizing, make sure your connections are at their top ability.   If they're not, then you'll be defeating your plans.

    One other point --- I learned there are different generations of JUMBO support.  This will come into play with someone older devices, but it is something to look out for also.
    LVL 1

    Author Comment

    I never considered the cabling.  It is cat 6 though.

    I did reboot the NAS.

    I was hoping I could test jumbo frame support one hop at a time.  I thought might do it.  I guess the best I can do is to test it to the switch then to the NAS.

    LVL 1

    Author Comment

    ok well i hooked the nas straight into the second nic on the server and it works fine now.  so it was the switch.  maybe i needed to power cycle it.  anyways this will work fine for me this way.

    thanks for the help.

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