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I have several sites, that on a local gigabit connection, a large ping (14kb or higher) will timeout. Pings that are smaller work fine.

This is happening a lot with Server 2003 boxes, but have (fewer) reports of it happening on 2008 R2.

Does anyone have any suggestions on where to start in troubleshooting this issue? Could it be switch related, or network,os/driver?

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What the MTU on the LAN? –  David Schwartz Aug 17 '12 at 1:08

1 Answer 1

Are you sure both the switch and the NIC can support a frame this large? If not then the host may be fragmenting the packet, which can lead to some odd results. There should be an option on the command line to specify the DF bit (Do Not Fragment) to prevent the auto fragmentation of the packet. If setting this flag causes the pings to fail altogether then you need to go back to making sure the MTU on the host and (especially) the switch are both sufficient and matching (nb - the most common jumbo MTU is 9K).

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