linux下 端口复用的问题

解决性参考：Currently, Linux does not allow reuse of same local port for both TCP server and TCP client.而且小测试程序能够成功，和我的库测试程序的差别也就在这一点了，因此接受连接和发起连接的端口分开即可。

其他资料：

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，需要改/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的情况(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可以绑定同一个端口；同样，使用SO_REUSEPORT选项，两个udp的socket可以绑定同一个端口。

3.linux下，两个tcp的socket不能绑定同一个端口；而如果使用SO_REUSEADDR选项，两个udp的socket可以绑定同一个端口。

4.freebsd下，两个tcp的socket绑定同一端口，只有第一个socket获得数据。

5.freebsd下，两个udp的socket绑定同一端口，如果数据包的目的地址是单播地址，则只有第一个socket获得数据，而如果数据包的目的地址是多播地址，则两个socket同时获得相同的数据。

6.linux下，两个udp的socket绑定同一端口，如果数据包的目的地址是单播地址，则只有最后一个socket获得数据，而如果数据包的目的地址是多播地址，则两个socket同时获得相同的数据。

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

Unix网络API

SO_REUSEADDR和SO_REUSEPORT

SO_REUSEADDR提供如下四个功能：

SO_REUSEADDR允许启动一个监听服务器并捆绑其众所周知端口，即使以前建立的将此端口用做他们的本地端口的连接仍存在。这通常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允许在同一端口上启动同一服务器的多个实例，只要每个实例捆绑一个不同的本地IP地址即可。对于TCP，我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允许单个进程捆绑同一端口到多个套接口上，只要每个捆绑指定不同的本地IP地址即可。这一般不用于TCP服务器。

SO_REUSEADDR允许完全重复的捆绑：当一个IP地址和端口绑定到某个套接口上时，还允许此IP地址和端口捆绑到另一个套接口上。一般来说，这个特性仅在支持多播的系统上才有，而且只对UDP套接口而言(TCP不支持多播)。

SO_REUSEPORT选项有如下语义：

此选项允许完全重复捆绑，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。

如果被捆绑的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：

在所有TCP服务器中，在调用bind之前设置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多次的多播应用程序时，设置SO_REUSEADDR选项，并将本组的多播地址作为本地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.