From mboxrd@z Thu Jan 1 00:00:00 1970 From: Willy Tarreau Subject: Re: SO_REUSEADDR not allowing server and client to use same port Date: Thu, 28 Feb 2008 21:36:17 +0100 Message-ID: <20080228203616.GD8953@1wt.eu> References: <47C6FA2A.5030302@alcatel-lucent.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel@vger.kernel.org, "Kittlitz, Edward (Ned)" , asweeney@alcatel-lucent.com, "Polhemus, William (Bart)" , netdev@vger.kernel.org To: Nebojsa Miljanovic Return-path: Received: from 1wt.eu ([62.212.114.60]:2201 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752510AbYB1Ug1 (ORCPT ); Thu, 28 Feb 2008 15:36:27 -0500 Content-Disposition: inline In-Reply-To: <47C6FA2A.5030302@alcatel-lucent.com> Sender: netdev-owner@vger.kernel.org List-ID: [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