Date: Mon, 1 Feb 1999 11:41:05 +1030 From: Greg Lehey <grog@lemis.com> To: Greg Black <gjb@comkey.com.au> Cc: FreeBSD Questions <questions@FreeBSD.ORG> Subject: Re: Excessive collisions on Ethernet Message-ID: <19990201114105.E8473@freebie.lemis.com> In-Reply-To: <19990131192548.24006.qmail@alpha.comkey.com.au>; from Greg Black on Mon, Feb 01, 1999 at 05:25:48AM %2B1000 References: <19990131110224.I8473@freebie.lemis.com> <19990131192548.24006.qmail@alpha.comkey.com.au>
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On Monday, 1 February 1999 at 5:25:48 +1000, Greg Black wrote: >> In the last few days I've noticed a really high number of collisions >> on my Ethernet. There are only 5 machines on the network, 3 of which >> are barely active, yet I see: >> >> (allegro, running 2.2.6-STABLE) >> ed0 1500 <Link> 00.00.c0.44.a5.68 43729816 45 43861788 12 977828 >> ed0 1500 widecast allegro 43729816 45 43861788 12 977828 > > That's only 1.1%. That's high for a small network. >> (freebie, running 4.0-CURRENT) >> Name Mtu Network Address Ipkts Ierrs Opkts Oerrs Coll >> ed2 1500 <Link> 00.80.48.e6.a0.61 11976144 12 13389307 0 988340 >> ed2 1500 widecast freebie 11976144 12 13389307 0 988340 > > And that's only 3.9% -- it's worse than allegro, but not by a > significant margin for the relatively small amount of traffic. > On my Ethernet, I have machines that report 0.01%, 9.6%, 0.7%, > 0.04% and 0.4%. The outlier is a machine that has been up a few > hours and was used for a large file transfer which blew its > average out of the water -- it'll be back to about 1% as time > goes by. Then you have problems too. >> I tried an ftp from panic, copying a file of 45 MB from freebie. The >> transfer ran at about 1 MB/s with about 450 collisions per second on >> the freebie side, none on the panic side. Here are the values before >> and after: >> >> freebie: >> Ipkts Ierrs Opkts Oerrs Coll >> before 11978350 13 13392678 0 989089 >> after 11994616 13 13424921 0 1009912 >> diff 16266 0 32243 0 20823 >> >> panic: >> Ipkts Ierrs Opkts Oerrs Coll >> before 480 0 651 1 0 >> after 32143 0 16679 1 0 >> diff 31663 0 16028 0 0 >> >> Looking at these results (40% collision rate on freebie), it would >> seem that something is seriously wrong in the network. On the other >> hand, allegro also shows a large number of collisions. At the moment >> I'm suspecting the (3 month old) Ethernet board in freebie, but I was >> wondering if there were other reasons which might apply. > > I just did some 10 to 15 MB file transfers with NFS on my LAN (I > don't have FTP set up), and saw collision rates ranging from 25% > to 35% for those periods. I'd say that was pretty normal, given > the way that Ethernet works. No, that's way too high. Genuine collisions happen on an Ethernet when two systems want to send a packet within a very small time window: first they look and listen, and if nothing is there, they send. If two send at pretty much *exactly* the same time, there will be a collision, from which they recover. If only one machine is sending at a time, there won't be collisions. If only a few are sending, there won't be many collisions. In general, you can consider 1% collisions to be an acceptable number. There's another thing of interest in this picture: in the example I showed above, collisions were at 40%. At this level, traffic on an Ethernet is becoming highly congested. Yet I got a transfer rate of just under 1 MB/s for the transfer, which suggests to me that the statistics may be bogus. A thing that just occurs to me is that it's always the ed driver that reports so many collisions, whereas the others don't. What kind of Ethernet board are you using? > The more interesting statistics are the overall figures over time, > and the ones you give at the start aren't too bad. Yes, freebie is > a bit high -- but 4% compared with 1% is not a big factor, > especially with the fairly low total amount of traffic. I'd watch > it for a bit longer before deciding it was a real problem. After > all, if you're getting 1 MB/s on a 10 Mb/s LAN, you're doing pretty > well :-) Well, the values for freebie are now: Name Mtu Network Address Ipkts Ierrs Opkts Oerrs Coll ed2 1500 <Link> 00.80.48.e6.a0.61 16493376 34 21501269 0 2326175 ed2 1500 widecast freebie 16493376 34 21501269 0 2326175 Since yesterday, that's 8 million more output packets and 1.3 million collisions. That suggests that something might be getting worse. Greg -- When replying to this message, please copy the original recipients. For more information, see http://www.lemis.com/questions.html See complete headers for address, home page and phone numbers finger grog@lemis.com for PGP public key To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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