Re: [RFC 0/2] Delayed binding of UDP sockets for Quic per-connection sockets

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

On Wed, Oct 31, 2018 at 7:30 PM Christoph Paasch <cpaasch@apple.com> wrote:
>
> Implementations of Quic might want to create a separate socket for each
> Quic-connection by creating a connected UDP-socket.
>
> To achieve that on the server-side, a "master-socket" needs to wait for
> incoming new connections and then creates a new socket that will be a
> connected UDP-socket. To create that latter one, the server needs to
> first bind() and then connect(). However, after the bind() the server
> might already receive traffic on that new socket that is unrelated to the
> Quic-connection at hand.

This can also be achieved with SO_REUSEPORT_BPF and a filter
that only selects the listener socket(s) in the group. The connect
call should call udp_lib_rehash and take the connected socket out
of the reuseport listener group. Though admittedly that is more
elaborate than setting a boolean socket option.

> The ideas for the implementation came up after a discussion with Ian
> and Jana re: their implementation of a QUIC server.

That might have preceded SO_TXTIME? AFAIK traffic shaping was the
only real reason to prefer connected sockets.