[ntp:questions] Re: Servers losing sync or not syncing at all.

Brian Utterback brian.utterback at sun.removeme.com
Tue Jan 3 20:09:23 UTC 2006

Danny Mayer wrote:
> Terje Mathisen wrote:
>> Danny Mayer wrote:
>>> TCPdump shows a lot of UDP checksum errors. I'd check your hardware.
>> This might not be relevant:
>> I have seen any number of TCP/UDP checksum errors over the last year,
>> and so far, _all_ of them have been on outgoing packets, i.e. they have
>> been logged on a system with a TOE (TCP Offload Engine) where the actual
>> checksum is calculated on the network card, after ethereal/snoop/tcpdump
>> have logged it.
>> Terje

Funny you mentioned it. I just this morning changed my preferences on
ethereal to not calculate the checksums since in my experience, they
almost never indicate a real error.

Your mileage may vary, of course. I deal in capture files from
diverse customers, but are skewed towards Sun hardware with
hardware checksum.

The point of this is that for outgoing packets that are outgoing
through interfaces that have TOE, the checksum will virtually
never be correct. Incoming is another matter, as are packets
outgoing through interfaces that do not have TOE.

So, if you always deal with incoming packets or do not have a TOE
capable interfaces, then the checksums are meaningful and your
experience is expected. If on the other hand, you are dealing with
outgoing packets on TOE interfaces, my experience is expected.


"Having them stolen may become our distribution model..."
Nicolas Negroponte on the Hundred Dollar Laptop.
Brian Utterback - OP/N1 RPE, Sun Microsystems, Inc.
Ph:877-259-7345, Em:brian.utterback-at-ess-you-enn-dot-kom

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