netdev - Re: [net-next RFC 0/4] SO

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Date:	Tue, 23 Feb 2016 21:06:13 -0800
From:	Tom Herbert <tom@...bertland.com>
To:	Gilberto Bertin <gilberto.bertin@...il.com>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [net-next RFC 0/4] SO_BINDTOSUBNET

On Tue, Feb 23, 2016 at 7:27 AM, Gilberto Bertin
<gilberto.bertin@...il.com> wrote:
> This series introduces support for the SO_BINDTOSUBNET socket option, which
> allows a listener socket to bind to a subnet instead of * or a single address.
>
> Motivation:
> consider a set of servers, each one with thousands and thousands of IP
> addresses. Since assigning /32 or /128 IP individual addresses would be
> inefficient, one solution can be assigning subnets using local routes
> (with 'ip route add local').
>
Hi Gilberto,

The concept is certainly relevant, but allowing binds by subnet seems
arbitrary. I can imagine that someone might want to bind to a list of
addresses, list of interfaces, list of subnets, or complex
combinations like a subnet on one interface, and list of addresses on
another. So I wonder if this is another use case for a BPF program on
a listener socket, like a program for a scoring function. Maybe this
could even combined with  BPF SO_REUSERPORT somehow?

Tom

> This allows a listener to listen and terminate connections going to any
> of the IP addresses of these subnets without explicitly configuring all
> of them. This is very efficient.
>
> Unfortunately there may be the need to use different subnets for
> different purposes.
> One can imagine port 80 being served by one HTTP server for some IP
> subnet, while another server used for another subnet.
> Right now Linux does not allow this.
> It is either possible to bind to *, indicating ALL traffic going to
> given port, or to individual IP addresses.
> The first only allows to accept connections from all the subnets.
> The latter does not scale well with lots of IP addresses.
>
> Using bindtosubnet would solve this problem: just by adding a local
> route rule and setting the SO_BINDTOSUBNET option for a socket it would
> be possible to easily partition traffic by subnets.
>
> API:
> the subnet is specified (as argument of the setsockopt syscall) by the
> address of the network, and the prefix length of the netmask.
>
> IPv4:
>         struct ipv4_subnet {
>                 __be32 net;
>                 u_char plen;
>         };
>
> and IPv6:
>         struct ipv6_subnet {
>                 struct in6_addr net;
>                 u_char plen;
>         };
>
> Bind conflicts:
> two sockets with the bindtosubnet option enabled generate a bind
> conflict if their network addresses masked with the shortest of their
> prefix are equal.
> The bindtosubnet option can be combined with soreuseport so that two
> listener can bind on the same subnet.
>
> Any questions/feedback appreciated.
>
> Thanks,
>   Gilberto
>
> Gilberto Bertin (4):
>   bindtosubnet: infrastructure
>   bindtosubnet: TCP/IPv4 implementation
>   bindtosubnet: TCP/IPv6 implementation
>   bindtosubnet: UPD implementation
>
>  include/net/sock.h                |  20 +++++++
>  include/uapi/asm-generic/socket.h |   1 +
>  net/core/sock.c                   | 111 ++++++++++++++++++++++++++++++++++++++
>  net/ipv4/inet_connection_sock.c   |  20 ++++++-
>  net/ipv4/inet_hashtables.c        |   9 ++++
>  net/ipv4/udp.c                    |  35 ++++++++++++
>  net/ipv6/inet6_connection_sock.c  |  17 +++++-
>  net/ipv6/inet6_hashtables.c       |   6 +++
>  8 files changed, 217 insertions(+), 2 deletions(-)
>
> --
> 2.7.1
>