"kernel: nf_conntrack: table full, dropping packets" on Oracle Linux 5 with UEK (Doc ID 1600601.1)

Last updated on AUGUST 01, 2017

Applies to:

Linux OS - Version Oracle Linux 5.5 with Unbreakable Enterprise Kernel [2.6.32] to Oracle Linux 5.9 with Unbreakable Enterprise Kernel [2.6.32] [Release OL5U5 to OL5U9]
Linux x86
Linux x86-64

Symptoms

Under high user load of around 5000 users (and above), the following error messages can be seen in /var/log/messages:

...
Sep 11 23:30:26 vm-db-node1 kernel: __ratelimit: 567 callbacks suppressed
Sep 11 23:30:26 vm-db-node1 kernel: nf_conntrack: table full, dropping packet.
Sep 11 23:30:26 vm-db-node1 last message repeated 9 times
Sep 11 23:30:31 vm-db-node1 kernel: __ratelimit: 925 callbacks suppressed
Sep 11 23:30:31 vm-db-node1 kernel: nf_conntrack: table full, dropping packet.
Sep 11 23:30:31 vm-db-node1 last message repeated 9 times
Sep 11 23:30:36 vm-db-node1 kernel: __ratelimit: 733 callbacks suppressed
Sep 11 23:30:36 vm-db-node1 kernel: nf_conntrack: table full, dropping packet.
Sep 11 23:30:36 vm-db-node1 last message repeated 9 times
Sep 11 23:30:41 vm-db-node1 kernel: __ratelimit: 1435 callbacks suppressed
Sep 11 23:30:41 vm-db-node1 kernel: nf_conntrack: table full, dropping packet.
Sep 11 23:30:41 vm-db-node1 last message repeated 9 times
Sep 11 23:30:46 vm-db-node1 kernel: __ratelimit: 1135 callbacks suppressed
Sep 11 23:30:46 vm-db-node1 kernel: nf_conntrack: table full, dropping packet.
Sep 11 23:30:46 vm-db-node1 last message repeated 9 times
Sep 11 23:30:51 vm-db-node1 kernel: __ratelimit: 902 callbacks suppressed
Sep 11 23:30:51 vm-db-node1 kernel: nf_conntrack: table full, dropping packet.
Sep 11 23:30:51 vm-db-node1 last message repeated 9 times
Sep 11 23:30:56 vm-db-node1 kernel: __ratelimit: 1019 callbacks suppressed
...


Even though both iptables and ip6tables were switched off and ipt_MASQUERADE is an iptables module, lsmod output shows:

 

Cause

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