Hi, 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. 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. The system is running at CentOS 6.3, we`re using Varnish 3.0.4 (from rpm).
We have optimized the following kernel parameters already: /proc/sys/net/ipv4/tcp_tw_reuse (now set to 1) /proc/sys/net/ipv4/tcp_tw_recycle (now set to 1) /proc/sys/net/ipv4/tcp_fin_timeout (now set to 30) /proc/sys/net/ipv4/tcp_keepalive_intvl (now set to 40) /proc/sys/net/ipv4/tcp_keepalive_time (now set to 1800) /proc/sys/net/ipv4/tcp_syn_retries (not set to 2) /proc/sys/net/ipv4/tcp_synack_retries (now set to 2) /proc/sys/net/ipv4/tcp_no_metrics_save (now set to 1) /proc/sys/net/ipv4/tcp_rmem (now 4096 87380 16777216) /proc/sys/net/core/wmem_max (now 16777216) /proc/sys/net/core/rmem_max (now 16777216) /proc/sys/net/ipv4/tcp_max_syn_backlog (now 4096) /proc/sys/net/ipv4/tcp_max_syn_backlog (now 4096) /proc/sys/net/core/netdev_max_backlog (now 5000) /proc/sys/net/ipv4/ip_local_port_range (now 1024 65536) I could not find anything at Google. May somebody give me tips how to resolve this issue? Thanks, Maxi ________________________________ Maximilian Herrmann, System Administrator Phone: +49 89 45 23 47 - 628 Fingerprint: 4BDD 79EA 8B40 F21C 9667 DC6C F257 0841 13DB 6EC5 jambit GmbH Erika-Mann-Str. 63, 80636 M?nchen Phone: +49 89 45 23 47 - 0 Fax: +49 89 45 23 47 - 70 http://www.jambit.com where innovation works Gesch?ftsf?hrer: Peter F. Fellinger, Markus Hartinger Sitz: M?nchen; Registergericht: M?nchen, HRB 129139
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