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Enabling Distributed Firewall on KVM impacts connection handling performance (2145463)

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When establishing a large number of connections between virtual machines, you may experience these symptoms:
  • Netperf may report errors similar to:

    shutdown_control: no response received errno 104

  • The issue seems to manifest itself when default firewall rules have been configured
  • With the default firewall rule configured, the issue do not manifest itself with a lighter load (For example: with 1 virtual machine x 64 sessions, or 8 virtual machines x 4 sessions)
  • The issue do not manifest itself if firewall rules are not configured (For example: Logical switches are put in the firewall exclusion list).
  • In the /var/log/syslog or /var/log/messages file, you see entries similar to:

    Apr 26 11:45:44 prmh-nsx-perf-server149 kernel: [1625289.950872] net_ratelimit: 239 callbacks suppressed
    Apr 26 11:45:44 prmh-nsx-perf-server149 kernel: [1625289.950875] nf_conntrack: table full, dropping packet
    Apr 26 11:45:44 prmh-nsx-perf-server149 kernel: [1625289.958436] nf_conntrack: table full, dropping packet

    Note: The preceding log excerpts are only examples. Date, time, and environmental variables may vary depending on your environment.


This issue occurs due to the fixed size of the conntrack table.


This is a known issue affecting VMware NSX-T 1.0.x.

Currently, there is no resolution.

To work around this issue, set the nf_conntrack_tcp_timeout_time_wait to 0 by running this command:

sysctl -w net.netfilter.nf_conntrack_tcp_timeout_time_wait=0

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