Extreme Slowdown using Gb Network

David Hubbard dhubbard at dino.hostasaurus.com
Tue Mar 25 12:49:00 CST 2003

Try running this script and see if it helps:
for f in /proc/sys/net/ipv4/conf/*/arp_filter; do
        echo 1 > $f
for f in /proc/sys/net/ipv4/conf/*/rp_filter; do
        echo 1 > $f


	-----Original Message-----
	From: Seumas Macmhicean [mailto:seumas at realise.com] 
	Sent: Tuesday, March 25, 2003 11:19 AM
	To: linux-poweredge at dell.com
	Cc: Unix Support
	Subject: RE: Extreme Slowdown using Gb Network

	I'll reply to a couple of responses at once - thanks all for

	>You said that "all other boxes on the network experience a
	>slowdown" when copying large files.  Do you mean that Box C is
	>delivering data to the public network when Box A is copying
files to Box 
	>B on the private Gb network?  Or is Box C slow in talking to
Box D on 
	>the private network when the transfers are happening? 

	To clarify - when copying largish files between boxes A and B,
all other boxes become 
	very unresponsive in general usage - reports on CPU, disk,
network and so on all appear normal. 
	Nothing appears in dmesg nor messages, but the other boxes chug
- even doing a simple 'ls'. 

	>What do the network traffic lights look like on both switches? 

	It's in the Co Location facility... will have to check another

	>Is there anything strange in the output of sar -n eth[01]? on
both the 
	>transfering and non-transfering systems? 

	We're going to investigate this. 

	>You could be having problems with the nics advertised
auto-negotiating and having problems with renegotiating 
	>during a heavy network load. 

	We're looking at ethtool but it seems to break the interface -
we'll keep at it and see if we can switch off the autonegotiation since
we don't need it (all devices on the network are the same - tg3)

	>This may sound like an obvious step, but have you verified that
you are using cat5E and not cat5 on these? 

	Interesting point - the cables were bought new for this build
and are about 2 months old - will have to check them explicitly (again -
Co-Location facility) but aren't they all Cat5e compatible nowadays?
Still, something to check.

	>Which model switch? 

	NetGear GS516T - bog standard config-free Gb switch 

	>Possibly, but any modern network switch acts as a multi-port
bridge, so 
	>your other boxes should not even see traffic. 

	Of course... but the effect is there - we'll do some more
thorough checks to make sure though... Hmmm. Faulty switch? 

	Something very odd is afoot here... 


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