Linux下端口复用(SO_REUSEADDR与SO_REUSEPORT)(转载)

http://blog.chinaunix.net/uid-7390305-id-2057201.html

做者：迷失千夏——拾露赏云

解决性参考：Currently, Linux does not allow reuse of same local port for both TCP server and TCP client.并且小测试程序可以成功，和个人库测试程序的差异也就在这一点了，所以接受链接和发起链接的端口分开便可。

其余资料：

这个是捣乱最大的：http://www.ajaxstu.com/Linuxbiancheng/294968.html　请问：linux难道没有端口重用吗？我用SO_REUSEPORT报找不到

已经搞定，须要改/usr/include/asm/socket.h:/* To add :#define SO_REUSEPORT 15 */

http://hi.baidu.com/qiaoyong/blo ... b1f4190ff47707.html

freebsd与linux下bind系统调用小结

只考虑AF_INET的状况（同一端口指ip地址与端口号都相同）
1.freebsd支持SO_REUSEPORT和SO_REUSEADDR选项,而linux只支持SO_REUSEADDR选项。
2.freebsd下,使用SO_REUSEPORT选项，两个tcp的socket能够绑定同一个端口；一样，使用SO_REUSEPORT选项，两个udp的socket能够绑定同一个端口。
3.linux下，两个tcp的socket不能绑定同一个端口；而若是使用SO_REUSEADDR选项，两个udp的socket能够绑定同一个端口。
4.freebsd下，两个tcp的socket绑定同一端口，只有第一个socket得到数据。
5.freebsd下，两个udp的socket绑定同一端口，若是数据包的目的地址是单播地址，则只有第一个socket得到数据，而若是数据包的目的地址是多播地址，则两个socket同时得到相同的数据。
6.linux下，两个udp的socket绑定同一端口，若是数据包的目的地址是单播地址，则只有最后一个socket得到数据，而若是数据包的目的地址是多播地址，则两个socket同时得到相同的数据。

http://cache.baidu.com/c?m=9d78d ... er=baidu&fast=y
Unix网络API

SO_REUSEADDR和SO_REUSEPORT
SO_REUSEADDR提供以下四个功能：
SO_REUSEADDR容许启动一个监听服务器并捆绑其众所周知端口，即便之前创建的将此端口用作他们的本地端口的链接仍存在。这一般是重启监听服务器时出现，若不设置此选项，则bind时将出错。 
SO_REUSEADDR容许在同一端口上启动同一服务器的多个实例，只要每一个实例捆绑一个不一样的本地IP地址便可。对于TCP，咱们根本不可能启动捆绑相同IP地址和相同端口号的多个服务器。 
SO_REUSEADDR容许单个进程捆绑同一端口到多个套接口上，只要每一个捆绑指定不一样的本地IP地址便可。这通常不用于TCP服务器。 
SO_REUSEADDR容许彻底重复的捆绑：当一个IP地址和端口绑定到某个套接口上时，还容许此IP地址和端口捆绑到另外一个套接口上。通常来讲，这个特性仅在支持多播的系统上才有，并且只对UDP套接口而言（TCP不支持多播）。 
SO_REUSEPORT选项有以下语义：
此选项容许彻底重复捆绑，但仅在想捆绑相同IP地址和端口的套接口都指定了此套接口选项才性。 
若是被捆绑的IP地址是一个多播地址，则SO_REUSEADDR和SO_REUSEPORT等效。 
使用这两个套接口选项的建议：
在全部TCP服务器中，在调用bind以前设置SO_REUSEADDR套接口选项； 
当编写一个同一时刻在同一主机上可运行屡次的多播应用程序时，设置SO_REUSEADDR选项，并将本组的多播地址做为本地IP地址捆绑。

What is the difference between SO_REUSEADDR and SO_REUSEPORT?
from：UNIX Socket FAQ 

SO_REUSEADDR allows your server to bind to an address which is in a TIME_WAIT state. It does not allow more than one server to bind to the same address. It was mentioned that use of this flag can create a security risk because another server can bind to a the same port, by binding to a specific address as opposed to INADDR_ANY. The SO_REUSEPORT flag allows multiple processes to bind to the same address provided all of them use the SO_REUSEPORT option. 

From Richard Stevens (rstevens@noao.edu):

This is a newer flag that appeared in the 4.4BSD multicasting code (although that code was from elsewhere, so I am not sure just who invented the new SO_REUSEPORT flag).

What this flag lets you do is rebind a port that is already in use, but only if all users of the port specify the flag. I believe the intent is for multicasting apps, since if you're running the same app on a host, all need to bind the same port. But the flag may have other uses. For example the following is from a post in February:

From Stu Friedberg (stuartf@sequent.com):

SO_REUSEPORT is also useful for eliminating the try-10-times-to-bind hack in ftpd's data connection setup routine. Without SO_REUSEPORT, only one ftpd thread can bind to TCP (lhost, lport, INADDR_ANY, 0) in preparation for connecting back to the client. Under conditions of heavy load, there are more threads colliding here than the try-10-times hack can accomodate. With SO_REUSEPORT, things work nicely and the hack becomes unnecessary. 

I have also heard that DEC OSF supports the flag. Also note that under 4.4BSD, if you are binding a multicast address, then SO_REUSEADDR is condisered the same as SO_REUSEPORT (p. 731 of "TCP/IP Illustrated, Volume 2"). I think under Solaris you just replace SO_REUSEPORT with SO_REUSEADDR.

From a later Stevens posting, with minor editing:

Basically SO_REUSEPORT is a BSD'ism that arose when multicasting was added, even thought it was not used in the original Steve Deering code. I believe some BSD-derived systems may also include it (OSF, now Digital Unix, perhaps?). SO_REUSEPORT lets you bind the same address *and* port, but only if all the binders have specified it. But when binding a multicast address (its main use), SO_REUSEADDR is considered identical to SO_REUSEPORT (p. 731, "TCP/IP Illustrated, Volume 2"). So for portability of multicasting applications I always use SO_REUSEADDR.