Some applications try to increase the buffers for performance reason. The
QUIC Go implementation for instance tries to request a 2048 kiB buffer
size.
The kernel default depends on skubuf size (which is architecture
dependent), but it is memory size independet and typically around 200 kiB
(see [1]).
Other network tuning guides suggest 16MiB for 1GB ethernet, as well as
changing the default as well as maximum bufffer size (see [2]). This
conservatively increases the maximum buffer size to 4MiB.
[1]: https://elixir.bootlin.com/linux/v5.15.45/source/include/net/sock.h#L2742
[2]: https://nateware.com/2013/04/06/linux-network-tuning-for-2013/
Enable IPv6 forwarding by default which is useful to run IPv6 based
OpenThread Border Router.
Currently Docker enables IPv4 forwarding by default. Enabling IPv6
support will enable IPv6 routing as well, but we are not ready yet to
enable IPv6 support for Docker at this point.
Enabling IPv6 forwarding should be harmless as there are no IPv6
addresses configured internally and Home Assistant OS is not typically
dual-homed. In cases where it is dual-homed (e.g. VPN), routing is
often used and firewalling is setup as part of that add-on.
Currently Linux has a limit of IGMP memberships of 20. When trying to
add membership to more than that, Linux fails with:
OSError: [Errno 105] No buffer space available
Allowing more memberships should not really be problematic as memory is
allocated dynamically when membership is actually added.
However, there is a protocol limit of how many memberships a host can be
in. The number of memberships needs to fit in a single group report
datagram of 64kB. In total 5459 group records fit in a datagram, but due
to IP header options this might be slightly smaller in practise.
(see https://github.com/home-assistant/core/issues/45957).
Use a limit of 1024, which should be plenty of headroom in both
directions.
Related to: https://github.com/home-assistant/core/issues/45957
