Messages in this thread | | | Date | Thu, 28 Feb 2008 21:36:17 +0100 | From | Willy Tarreau <> | Subject | Re: SO_REUSEADDR not allowing server and client to use same port |
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[cc'd netdev]
On Thu, Feb 28, 2008 at 12:15:06PM -0600, Nebojsa Miljanovic wrote: > Hello all, > I have seen similar complaints about this issue before in the list archive, but > I have not seen any resolution. So, I am posting the question again in hope of > getting some replies. > > Currently, Linux does not allow reuse of same local port for both TCP server and > TCP client. I understand that there may be a need to prevent two servers from > binding to the same local port, but having 1 server and 1 outgoing client use it > should be allowed. Other Unix like operating systems do allow it.
I've been encountering the need for SO_REUSEPORT as implemented on some BSD for instance. It allows any process to explicitly permit another one to bind to the same IP:port provided that it also sets its socket with SO_REUSEPORT. This is a real requirement when you need to restart a service without any service disruption.
In the end, I've written a trivial patch for 2.4 (but most likely 2.6 would use nearly the same one). I noticed that the conflict detection logic already distinguished between 3 cases: sk->reuse==0, sk->reuse==1, sk->reuse >1. sk->reuse was set to 1 with SO_REUSEADDR. I simply had to make SO_REUSEPORT do sk->reuse |= 2 to get everything working as expected.
I don't know yet if it is as easy to do in 2.6, but if there is a possible acceptance of including this useful feature into mainline, I can try to work a patch (possibly cleaner than my existing one for 2.4).
Regards, Willy
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