Bug#861115: Please consider increasing net.ipv6.route.max_size default value

[Tim Bray <tim@provu.co.uk>]

On 21/01/2020 19:37, Vincent Bernat wrote:
> This setting is for the size of the route cache. You can have far more
> routes. In the past, there were bugs where each lookup will be put in
> cache, but since 4.2, only the PMTU exceptions are stored in cache. See
> <https://vincent.bernat.ch/en/blog/2017-ipv6-route-lookup-linux#caching>
>
> Do you have a lot of entries in `ip -6 route show cache`?


No entries at all in
`ip -6 route show cache`

and none in `ip -6 route show table cache`

It is a quiet time of day, so I'll check again.

What prompted me to look at net.ipv6.route.max_size was because I built my own newer kernel (in desperation).

Linux version 5.4.11 (from kernel.org, .config from debian buster, make olddefconfig) gives out in dmesg:

Route cache is full: consider increasing sysctl net.ipv[4|6].route.max_size.


I've never seen this message on 4.19 Debian buster,  but increasing net.ipv6.route.max_size made all the network hangs go away, both on 5.4.11 and 4.19

Tim Bray