loopback address problem in Fedora
 

Hi,

I'm using Fedora 14 (I encountered same problem in the other versions). I'm trying to do socket programming for IPv6. But I always get the same error: "bind error". I coded all program to IPv6 (AF_INET6, sockaddr_in6, sin6_family, ..etc). I think that bind use the Ipv6 lo address ::1. I ping to ::1 address and I access that. But I don't understand that bind don't access that.

thank in advance

The default for Linux is that an attempt to bind with "::" as the local address ALSO binds "0.0.0.0" over in the IPv4 space. If you already have a separate socket bound to "0.0.0.0" for the same port number, then doing this with IPv6 will collide. There are two ways around this:

1. Only bind to the IPv6 and it let it also handle the IPv4 connections on this one socket.

2. Change the behavior system wide with: sysctl -w net.ipv6.bindv6only=1

If you choose method #2 it will affect all programs, where others might need to be reconfigured to specifically listen on 2 sockets to listen to both IPv4 and IPv6. Also, if you want this to be persistent across reboots, you need to configure an init/rc script to do that command (again).