Date: Mon, 01 Feb 1999 22:37:40 +1000 From: Greg Black <gjb@comkey.com.au> To: Greg Lehey <grog@lemis.com> Cc: FreeBSD Questions <questions@FreeBSD.ORG> Subject: Re: Excessive collisions on Ethernet Message-ID: <19990201123740.27312.qmail@alpha.comkey.com.au> In-Reply-To: <19990201114105.E8473@freebie.lemis.com> of Mon, 01 Feb 1999 11:41:05 %2B1030 References: <19990131110224.I8473@freebie.lemis.com> <19990131192548.24006.qmail@alpha.comkey.com.au> <19990201114105.E8473@freebie.lemis.com>
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> >> 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. Well, that's not my understanding. I'd have considered anything from 0.1% to 2.0% to be reasonable. > >> (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 don't perceive any problems. And I'm hard pressed to believe that an Ethernet that runs at pretty much its rated speed and has collisions below 1% for all the significant data has problems -- but maybe that's a matter of different opinions. > > 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. Surely an ftp transfer involves plenty of packets going in *both* directions and so can be expected to produce a fair number of collisions? > 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. I reported 1% collisions above, but you said I had problems. I'm not sure what level of collisions you feel represents a problem. As I understand the way it works, errors are a problem but collisions are ok in some (smallish) numbers. > 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? Here are some data from my Ethernet: maxim up 73+01:12, 0 users, load 0.05, 0.07, 0.07 alice up 30+06:32, 2 users, load 0.13, 0.09, 0.08 alpha up 4+03:55, 3 users, load 0.13, 0.09, 0.03 bravo up 4+03:55, 0 users, load 0.00, 0.00, 0.00 Name Mtu Network Address Ipkts Ierrs Opkts Oerrs Coll ef0 1500 <link1> 00:60:08:ac:d7:1b 5781293 16 11978534 12 7189 ef0 1500 203.9.155.2 maxim 5781293 16 11978534 12 7189 ef0 1500 192.168.1 192.168.1.1 5781293 16 11978534 12 7189 Name Mtu Network Address Ipkts Ierrs Opkts Oerrs Coll eb0 1500 <link1> 00:60:08:a8:17:5d 4898485 1 2485013 0 52390 eb0 1500 203.9.155.2 alice 4898485 1 2485013 0 52390 eb0 1500 192.168.1 192.168.1.2 4898485 1 2485013 0 52390 Name Mtu Network Address Ipkts Ierrs Opkts Oerrs Coll xl0 1500 <Link> 00.10.4b.18.1f.b9 25057 0 26207 0 4340 xl0 1500 192.168.1 alpha 25057 0 26207 0 4340 Name Mtu Network Address Ipkts Ierrs Opkts Oerrs Coll xl0 1500 <Link> 00.10.4b.18.1f.a8 15808 0 8428 0 2 xl0 1500 192.168.1 bravo 15808 0 8428 0 2 maxim is an old 486-33 running BSD/OS-3.1 with a 3C509, alice is a Pentium-166 running BSD/OS-3.1 with a 3C900, alpha and bravo are Celeron-300A's running FreeBSD-2.2.8-Release with 3C900B's. The errors on maxim were from the time when it booted and the rest of the LAN was out to lunch. The others all booted more recently on to a live network. The experiments I tried with the NFS copies were between alpha and alice and bumped alpha's collisions from virtually zero to the present figure. > > 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. Yes, it does look as though it's getting worse. You may indeed have a fault somewhere. I'd certainly check the cables first, and try swapping some of them around before pulling cards from machines. (I have to pull video cards from five machines tomorrow to swap them for something that works with FreeBSD, so I'm a bit jaundiced about pulling cards at the moment :-) ) Greg -- Greg Black <gjb@acm.org> To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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