Date: Thu, 8 Feb 1996 21:23:47 -0800 (PST) From: Julian Elischer <julian@ref.tfs.com> To: koshy@india.hp.com (A JOSEPH KOSHY) Cc: hackers@FreeBSD.ORG Subject: Re: tcpdump / kernel dropping packets Message-ID: <199602090523.VAA02802@ref.tfs.com> In-Reply-To: <199602090427.AA168780028@fakir.india.hp.com> from "A JOSEPH KOSHY" at Feb 9, 96 09:57:06 am
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> > > Hi, > > I was testing my network driver and found that `tcpdump' was experiencing > a very high packet drop rate. This is normal > > If I run "tcpdump" without the "-n" option, I find (a) the output on > screen is `bursty' with long periods of silence (b) at the end of the run > tcpdump reports typically 90% of the packets "dropped by kernel". everything backs up while tcpdump is trying to resolve a name that needs to be remotely looked up. > > If I run "tcpdump" with the "-n" option (no resolving of IP addresses) > it runs with a much smaller loss percentage (but still != 0). of course, there are no lookups to do... > > I'd like to know if this behaviour is normal or whether there is something > wrong with my network setup (read: my driver :)). normal. > > If normal, what can I do reduce packet loss (eg if FreeBSD is to be the basis > for a network analyser tool?). > save the packets to disk and analyse them offline. (use tcpdump -w filename and tcpdump -r (options) filename > I'm running FreeBSD 2.1.0-R on an 8MB P90 IDE system. The network card is > an HPPCLan+ with "if_ed.c" hacked up to support it. The driver is otherwise > stable and has been working well for a month now. I'm trying to tune/improve > performance at the moment. it would be better for offline analysis if you used scsi because the heavy use of CPU in IDE might still cause a few lost packets, but hopefully not too many. > > On this topic, I'd appreciate any pointers on how to measure the effectiveness > of ethernet drivers (short of requiring special purpose hardware to be used). > I'd like to know if I'm dropping packets, sending out too many packets, > munging the network etc. > good question... ping a reliable host? > Koshy >
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