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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: Ethernet NAPs (was Re: Miami ...)
I just have to speek up that this is all very well and good, but it's also a good way to make a NAP that doesn't work. _ALL_ devices on a layer-2 fabric need to have the same MTU. That means if there are any FastEthernet or Ethernet connected members 1500 bytes is it. It also means if you pick a larger value (4470, 9k) _ALL_ members must use the same value. If you don't, the behavior is simple. A 9k MTU GigE arps for a 1500 byte FastEthernet host. Life is good. The TCP handshake completes, life is good. TCP starts to send a packet, putting a 9k frame on the wire. Depending the switch, the switch either drops it as over MTU for the FastEthernet, or the FastEthernet card cuts it off at 1500 bytes, and counts it as an errored frame (typically with a jabber or two afterwards) and no data flows. A larger MTU is a fine plan, but make sure if you try that anywhere that the switch is set for the larger sizes and all devices are capable of that larger frame size, or you're in trouble. -- Leo Bicknell - [email protected] Systems Engineer - Internetworking Engineer - CCIE 3440 Read TMBG List - [email protected], www.tmbg.org
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