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'). 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