Re: paket loss on freebsd router if (b)snmpd is running##SPAM

On Fri, 27 Oct 2006, Thomas wrote:

T>Hello Harti
T>
T>Harti Brandt schrieb:
T>> On Fri, 27 Oct 2006, Thomas wrote:
T>>
T>> T>Hello
T>> T>
T>> T>I use several 5.4 and 6.1 FBSD machines as router (with quagga). The
T>> T>average traffic is 300mbit/s (em interfaces with polling enabled). It
T>> T>works more or less.
T>> T>
T>> T>Problem:
T>> T>If bsnmpd is running and I'm doing a snmpwalk from a remote machine the
T>> T>router has some significant packet loss. We are talking about 3-15% of
T>> T>packet loss. It's a simple snmpwalk (ipRouteTable and the interfaces stats).
T>>
T>> Does this happen also if you walk only the interface tables? What size is
T>> your routing table?
T>
T>The routing table has approx. 200k entries. I've to correct my
T>statement. I don't walk over the RoutingTable.

Oh. That would be a nice test how good the RB-tree implementation of the
routing table is :-)

T>It's only an interface table walk (IF-MIB). bsnmpd consumes approx.
T>6-10% cpu. I already have significant packet loss if bsnmpd is started.
T>
T>bsnmpd not running:
T>
T>ping www.switch.ch
T>
T>--- oreius.switch.ch ping statistics ---
T>44 packets transmitted, 44 packets received, 0% packet loss
T>round-trip min/avg/max/stddev = 6.825/7.425/8.007/0.252 ms
T>
T>zero packet loss.
T>
T>
T>netstat -w 1 shows no error.
T>
T> input (Total) output
T> packets errs bytes packets errs bytes colls
T> 39877 0 34330807 38614 0 34087518 0
T> 45522 0 38730142 44124 0 38424881 0
T> 44671 0 38783909 43455 0 38604698 0
T> 43140 0 36939542 42059 0 36691583 0
T> 43428 0 36858817 42213 0 36700954 0
T> 43748 0 37994949 42687 0 37780190 0
T> 42698 0 36451927 41409 0 36270936 0
T> 38695 0 32184588 37119 0 31791417 0
T>
T>
T>
T>
T>bsnmpd started:
T>
T>ping www.switch.ch
T>--- oreius.switch.ch ping statistics ---
T>57 packets transmitted, 53 packets received, 7% packet loss
T>round-trip min/avg/max/stddev = 6.715/12.638/95.183/19.041 ms
T>
T>7% packet loss.
T>
T>
T>netstat shows some errors too.
T>netstat -w 1
T> input (Total) output
T> packets errs bytes packets errs bytes colls
T> 33597 0 27508009 32433 0 27344720 0
T> 38204 0 32117848 36950 0 31852251 0
T> 39171 0 33870984 37999 0 33696346 0
T> 32160 0 26825650 31065 0 26591079 0
T> 26915 726 20902878 25771 0 20791170 0
T> 35167 0 29173014 33945 0 28904867 0
T> 33282 370 27478393 32140 0 27297079 0
T> 29738 0 23859586 28464 0 23524984 0
T> 38456 598 31559055 36881 0 31313396 0
T> 34738 0 28088584 33247 0 27743827 0
T> 38193 648 30854513 36657 0 30556948 0
T>
T>
T>A snmpwalk makes it a bit worse but not much. I already have packet loss
T>if bsnmpd is just started without any walks.

You mean, you have loss if it is just ideling around? The only thing
bsnmpd does in this situation is polling the interface statistics, which
is needed because the kernel has only 32-bit counters. Could you please
check what the polling interval is? You find this in the BEGEMOT-MIB2-MIB.
Something like

snmpwalk ... <host> begemotMib2

given that /usr/share/snmp/mibs is in your MIB path.

harti
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