[Pdns-users] Heads up Linux IPv6 users: larger scale use may require kernel tuning

bert hubert bert.hubert at netherlabs.nl
Thu Feb 27 19:40:23 UTC 2014

Hi everybody,

More and more deployments are switching on IPv6, some of them are even
'switching over', by giving mobile devices only an IPv6 address and
utilizing DNS64/NAT64 to make this work for IPv4 legacy services. We
describe this on

However, today we had a Linux user run into problems with their large IPv6
deployment. The root cause turned to be in the Linux kernel.

If you are doing larger scale IPv6 on Linux, check:

$ sysctl net.ipv6.route.max_size

The kernel-level default is 4096. If you have more IPv6 users than this
active simultaneously, things will slow down to a crawl. Today we raised the
value to 16384, but far higher values are probably safe too and may be

We're discussing this the the relevant Linux kernel people here
http://marc.info/?l=linux-netdev&m=139352943109400&w=2 but for now, things
need to be set manually.

Good luck with your IPv6 deployments!


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