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<p class="MsoNormal"><span lang="EN-US">Hi,</span></p>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
<p class="MsoNormal"><span lang="EN-US">i`m currently having issues with my Varnish load balancers. For some users, the access to our site is very slow, for others it isn`t reachable.</span></p>
<p class="MsoNormal"><span lang="EN-US">I`ve observed something strange at the dmesg-Logfile, it is saying “possible SYN flooding on port 80. Sending cookies.” about every 20 minutes. I don`t think that this is a real SYN flood, as this is some very high traffic
system.</span></p>
<p class="MsoNormal"><span lang="EN-US">The system is running at CentOS 6.3, we`re using Varnish 3.0.4 (from rpm).</span></p>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
<p class="MsoNormal"><span lang="EN-US">We have optimized the following kernel parameters already:</span></p>
<p class="MsoNormal"><span lang="EN-US">/proc/sys/net/ipv4/tcp_tw_reuse (now set to 1)</span></p>
<p class="MsoNormal"><span lang="EN-US">/proc/sys/net/ipv4/tcp_tw_recycle (now set to 1)</span></p>
<p class="MsoNormal"><span lang="EN-US">/proc/sys/net/ipv4/tcp_fin_timeout (now set to 30)</span></p>
<p class="MsoNormal"><span lang="EN-US">/proc/sys/net/ipv4/tcp_keepalive_intvl (now set to 40)</span></p>
<p class="MsoNormal"><span lang="EN-US">/proc/sys/net/ipv4/tcp_keepalive_time (now set to 1800)</span></p>
<p class="MsoNormal"><span lang="EN-US">/proc/sys/net/ipv4/tcp_syn_retries (not set to 2)</span></p>
<p class="MsoNormal"><span lang="EN-US">/proc/sys/net/ipv4/tcp_synack_retries (now set to 2)</span></p>
<p class="MsoNormal"><span lang="EN-US">/proc/sys/net/ipv4/tcp_no_metrics_save (now set to 1)</span></p>
<p class="MsoNormal"><span lang="EN-US">/proc/sys/net/ipv4/tcp_rmem (now 4096 87380 16777216)</span></p>
<p class="MsoNormal"><span lang="EN-US">/proc/sys/net/core/wmem_max (now 16777216)</span></p>
<p class="MsoNormal"><span lang="EN-US">/proc/sys/net/core/rmem_max (now 16777216)</span></p>
<p class="MsoNormal"><span lang="EN-US">/proc/sys/net/ipv4/tcp_max_syn_backlog (now 4096)</span></p>
<p class="MsoNormal"><span lang="EN-US">/proc/sys/net/ipv4/tcp_max_syn_backlog (now 4096)</span></p>
<p class="MsoNormal"><span lang="EN-US">/proc/sys/net/core/netdev_max_backlog (now 5000)</span></p>
<p class="MsoNormal"><span lang="EN-US">/proc/sys/net/ipv4/ip_local_port_range (now 1024 65536)</span></p>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
<p class="MsoNormal"><span lang="EN-US">I could not find anything at Google. May somebody give me tips how to resolve this issue?</span></p>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
<p class="MsoNormal"><span lang="EN-US">Thanks,</span></p>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
<p class="MsoNormal"><span lang="EN-US">Maxi</span></p>
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<font face="calibri" color="Gray" size="2"><br>
Maximilian Herrmann, System Administrator<br>
Phone: +49 89 45 23 47 - 628<br>
Fingerprint: 4BDD 79EA 8B40 F21C 9667 DC6C F257 0841 13DB 6EC5 <br>
<br>
jambit GmbH<br>
Erika-Mann-Str. 63, 80636 München<br>
Phone: +49 89 45 23 47 - 0 Fax: +49 89 45 23 47 - 70<br>
<br>
http://www.jambit.com where innovation works<br>
<br>
Geschäftsführer: Peter F. Fellinger, Markus Hartinger<br>
Sitz: München; Registergericht: München, HRB 129139<br>
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