[Scottish] Network notwork

Craig Perry Craig.Perry at sanmex.com
Tue Jan 31 09:34:41 GMT 2006


I saw something similar a while back, it was caused by loss of packets
through a router at the far end of an LFN.

Basically losing like 2% of packets, equated to a drop of 50%-60% in
throughput which i thought was rather insane but hey...

It was reasonably similar symptoms in that there were *shedloads* of
duplicate ACKs, because the network was dropping a packet or two in one
direction, and for some reason or other unbeknown to me, it is normal
for a device to duplicate an ACK when it receieves packets out of
sequence, or is genuinely just missing a packet... or something like
that... it was a few months ago now...

Bascially i saw improvements by messing around with the MTU, i think i
decreased it significantly.

I corrected it by replacing the router (actually it was one of those
horrible "switch based routers" :-s)



-----Original Message-----
From: scottish-bounces at mailman.lug.org.uk
[mailto:scottish-bounces at mailman.lug.org.uk] On Behalf Of Colin McKinnon
Sent: 30 January 2006 21:28
To: SLUG-list
Subject: [Scottish] Network notwork

Hi all,

Obviously my last question just wasn't tough enough....so, this time for
a bonus ball...

What would cause *lots* of DUP ACKs / Retransmits on a LFN?

(10 Mb internet connection, lots of clients at site connecting. 80% + of
packets going out to remote server are DUP ACK, 80% + of inward packets
are retransmits. Effect is that clients get next to no bandwidth to
server. Only occurs with work-related application server - they can
access other systems with noi apparrent problem, other sites do not have
same problem accessing same server)



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