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</o:shapelayout></xml><![endif]--></head><body lang=DA link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>Well it’s been awhile, but I think I can safely say this has been resolved.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>Thanks to all who offered suggestions.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>It turned out it was a simple buffer problem on the linux servers.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>netstat –su showed a very large amount of udp packet receive errors.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>The problem is that the default network buffers in linux are way too small.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>After changing kernel settings to :<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p style='margin:0cm;margin-bottom:.0001pt'><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif"'>net.core.rmem_max = 16777216<o:p></o:p></span></p><p style='margin:0cm;margin-bottom:.0001pt'><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif"'>net.core.wmem_max = 16777216<o:p></o:p></span></p><p style='margin:0cm;margin-bottom:.0001pt'><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif"'>net.ipv4.tcp_rmem = 4096 87380 16777216<o:p></o:p></span></p><p style='margin:0cm;margin-bottom:.0001pt'><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif"'>net.ipv4.tcp_wmem = 4096 65536 16777216<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>All problems disappeared.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>We have now been running for 2 months like this and without a single fault.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>More info on can be found here:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>http://m0dlx.com/blog/Severe_UDP_packet_loss.html<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><div><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>Regards,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>Bjarne Blichfeldt<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p></div><div style='border:none;border-left:solid blue 1.5pt;padding:0cm 0cm 0cm 4.0pt'><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> Bjarne Blichfeldt <br><b>Sent:</b> 3. september 2010 17:18<br><b>To:</b> 'Users of ISC DHCP'<br><b>Subject:</b> Performance issue ( maybe )<o:p></o:p></span></p></div></div><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>We have (become) what seems to be a periodic performance problem in our setup. <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>I am trying to figure out what we have changed lately, it might be load related.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>During clients startup, the servers takes a very long time ~20-30 seconds to answer a DISCOVER. <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>The server then answers with OFFER. But since the server took so long to answer, the client has timed out and sends a new DISCOVER.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>When the first OFFER reach the client, the IP transaction ID does not match and the client drops the first OFFER<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>Example :<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Client Server<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> DISCOVER (transaction ID 1) </span><span lang=EN-US style='font-family:Wingdings'>à</span><span lang=EN-US><o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> :time goes<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> timeout<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> DISCOVER (transaction ID 2) </span><span lang=EN-US style='font-family:Wingdings'>à</span><span lang=EN-US><o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> </span><span lang=EN-US style='font-family:Wingdings'>ß</span><span lang=EN-US> OFFER (transaction ID <span style='color:#1F497D'>1</span>)<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> ignored from client<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US> DISCOVER </span><span lang=EN-US style='font-family:Wingdings'>à</span><span lang=EN-US><o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> and so on.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>This is found by tracing on the switch where the server is connected, that is directly at the server port.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>Looking at the servers with top when everything works :<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Cpu0 : 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Cpu1 : 0.3%us, 0.3%sy, 0.0%ni, 99.3%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Cpu2 : 0.0%us, 0.3%sy, 0.0%ni, 95.3%id, 4.3%wa, 0.0%hi, 0.0%si, 0.0%st<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Cpu3 : 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Mem: 2075208k total, 714656k used, 1360552k free, 189160k buffers<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Swap: 4128760k total, 100k used, 4128660k free, 318604k cached<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>During the problem I see something like (numbers added from memory):<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Cpu0 : 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Cpu1 : 0.3%us, 0.3%sy, 0.0%ni, 99.3%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st<o:p></o:p></span></p><p class=MsoListParagraph style='text-indent:-18.0pt;mso-list:l1 level1 lfo2'><![if !supportLists]><span lang=EN-US style='font-family:Wingdings'><span style='mso-list:Ignore'>è<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span lang=EN-US>Cpu2 : 0.0%us, 0.3%sy, 0.0%ni, 1.3%id, 98%wa, 0.0%hi, 0.0%si, 0.0%st<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Cpu3 : 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Mem: 2075208k total, 714656k used, 1360552k free, 189160k buffers<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Swap: 4128760k total, 100k used, 4128660k free, 318604k cached<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>The only process really working is kjournald.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>Now I am a little in the dark as what to do now. First of course is to offload everything but dhcpd from the servers to<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>reduce any load I haven’t noticed. There were a few java programs and a mysql server on dhcp2, Those are now closed ,nothing extra on dhcp1. <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>The next I have done is to increase default lease time from 8 hours to 5 days.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>so my questions are:<o:p></o:p></span></p><p class=MsoListParagraph style='text-indent:-18.0pt;mso-list:l0 level1 lfo4'><![if !supportLists]><span lang=EN-US><span style='mso-list:Ignore'>1)<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span lang=EN-US>anybody seen something similar ?<o:p></o:p></span></p><p class=MsoListParagraph style='text-indent:-18.0pt;mso-list:l0 level1 lfo4'><![if !supportLists]><span lang=EN-US><span style='mso-list:Ignore'>2)<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span lang=EN-US>Good ideas to further investigate ? What about the network topology ? Any gotcha’s when sending DISCOVERY through two cisco routers ?<o:p></o:p></span></p><p class=MsoListParagraph style='text-indent:-18.0pt;mso-list:l0 level1 lfo4'><![if !supportLists]><span lang=EN-US><span style='mso-list:Ignore'>3)<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span lang=EN-US>During the problem, everything starts to go wrong. What would be some good values in the failover paragraph to ease the system ?<o:p></o:p></span></p><p class=MsoListParagraph><span lang=EN-US>I think I will have to increase mctl, but not too much. That will create problem in partner down.<o:p></o:p></span></p><p class=MsoListParagraph><span lang=EN-US>I see a lot of load balancing messages in the logfile. Any way of changing the load balancing to reduce load ? <o:p></o:p></span></p><p class=MsoListParagraph><span lang=EN-US><o:p> </o:p></span></p><pre><span lang=EN-US style='font-family:"Calibri","sans-serif";color:#1F497D'>Also, what would be the consensus of disabling pingcheck ? <o:p></o:p></span></pre><pre><b><span lang=EN-US>ping-check</span></b><span lang=EN-US> false;<o:p></o:p></span></pre><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>The ping adds at least one second to every discovery/offer, and that could maybe contribute to our problem since we have a large net with<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>many net boxes between the server and the clients<o:p></o:p></span></p><p class=MsoListParagraph><span lang=EN-US> <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>And last, when this happens, I could use some good ideas on how to handle it in the shortest possible time.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>The last time we had this, I shut one server down, we stopped all incoming dhcp requests on one server, put the other server in<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>partner down and opened for dhcp request step by step from the different subnets. After a few nets where online, we started the second<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>dhcp server, waited for recover to finish.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>That took a long time – about 2 hours. The users where not happy.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>The installation details are :<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>Topology : Windows clients </span><span lang=EN-US style='font-family:Wingdings'>à</span><span lang=EN-US> 2 cisco routers </span><span lang=EN-US style='font-family:Wingdings'>à</span><span lang=EN-US> 2 dhcp linux servers<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>RHEL 5 two interfaces eth0+eth1 bundled into bond0<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Linux version 2.6.18-194.11.1.el5<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>dhcp1 : 4 x 3.2 GHz Xeon cpu, 2GB Ram, 72 GB disk<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>dhcp2 : 4 x 3.2 GHz Xeon cpu, 4 GB Ram, 72 GB Disk<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>isc-dhcpd 4.1.1-P1<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>failover protocol<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>1352 subnets<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>792 pools<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>around 7500 active leases<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>extract from dhcpd.conf :<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>ddns-update-style none;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> authoritative ;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>default-lease-time 432000 ; (was 8 hours)<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>max-lease-time 604800 ;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>omapi-port 7911 ;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US># Failover configuration.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>failover peer "ipc-dhcp1-ipc-dhcp2" {<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> primary;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> address 10.11.90.73;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> port 647;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> peer address 10.11.90.74;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> peer port 647;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> max-response-delay 90;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> max-unacked-updates 20;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> mclt 1800;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> split 128;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> load balance max seconds 5;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>}<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US># typical subnet :<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>subnet 10.2.2.0 netmask 255.255.255.0 {<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> option subnet-mask 255.255.255.0 ;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> option routers 10.2.2.254 ;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> option domain-name "name.local" ;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> option option-150 10.11.75.10 ;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> filename "<a href="file:///\\mboot.0">\\mboot.0</a>" ;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> next-server 10.2.2.240 ;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> pool {<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> range 10.2.2.1 10.2.2.200;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> failover peer "ipc-dhcp1-ipc-dhcp2";<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> deny dynamic bootp clients;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> }<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>}<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='font-size:8.0pt;font-family:"Verdana","sans-serif"'>Regards,</span><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'><o:p></o:p></span></p><p class=MsoNormal style='margin-bottom:12.0pt'><b><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'>Bjarne Blichfeldt</span></b><b><span style='font-size:9.0pt;font-family:"Verdana","sans-serif"'> </span></b><span style='font-size:9.0pt;font-family:"Verdana","sans-serif"'><o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p></div></div></body></html>