Are you unable to restart DNS due to TCP_FASTOPEN? We can help you.

As part of our Server Management Services, we assist our customers with several similar queries.

Today, let us see procedure followed by our Support Techs in order to perform this task.

Unable to restart DNS due to TCP_FASTOPEN

Typically, when restarting the Named DNS service, you may encounter the following error preventing the DNS Service from restarting.

named[8400]: ../../../../lib/isc/unix/socket.c:5682: unexpected error:
named[8400]: setsockopt(23, TCP_FASTOPEN) failed with Protocol not available

When the kernel feature TCP_FASTOPEN is not enable, this can cause the DNS service fail to restart.

Most kernels do enable this, and you can easily check and verify if this is enabled with a quick check from the command line interface.

You can also do this via the terminal interface in the WHM. Home » Server Configuration » Terminal.

Today, let us see the simple steps followed by our Support Techs.

Firstly, to verify if this is enable on the server run the following:

cat /proc/sys/net/ipv4/tcp_fastopen

If this returns a value of 0, it is disable.

If this returns a 1, this means it is only enable for outgoing client connections, and a 2 indicates it is available on the server.

Setting this to 3 will enable both of those options.

echo "3" > /proc/sys/net/ipv4/tcp_fastopen

If you would like to keep this through a reboot, echo the following into a new .conf file.

echo "net.ipv4.tcp_fastopen=3" > /etc/sysctl.d/30-tcp_fastopen.conf

[Need help with similar query? We’d be glad to assist you]

Conclusion

In short, today we saw steps followed by our Support Techs to resolve issue which makes unable to restart DNS due to TCP_FASTOPEN.