I'm having a problem with a dedicated server, I don't known if it's the default behavior but this is the problem: If I connect to a service located on the server with localhost the service gets as source IP the external IP. Let me show an example, I use netcat for listening on 127.0.0.1:4444 xxxxxx # nc -vv -l -s 127.0.0.1 -p 4444 listening on [127.0.0.1] 4444 ... Lets check if it's ok: xxxxxx ~ # netstat -atnp | grep 4444 tcp 0 0 127.0.0.1:4444 0.0.0.0:* LISTEN 14038/nc Ok lets connect: xxxxxx ~ # nc -vv 127.0.0.1 4444 localhost [127.0.0.1] 4444 (?) open Return to the tty that have the listening process and I get this: connect to [127.0.0.1] from xxxxxx.net [176.31.xxx.xx] 50354 So that's the problem. I have a server daemon that have to listen on localhost and checks that the ip is 127.0.0.1 when the client connects but for some reason when I connect to localhost it reports the external ip... If I do the same with IPv6 it works as excepted... Detects connection as localhost (::1). Some info that can be useful: "localhost" resolves without problems to 127.0.0.1 xxxxxx ~ # ping -c1 localhost PING localhost (127.0.0.1) 56(84) bytes of data. 64 bytes from localhost (127.0.0.1): icmp_req=1 ttl=64 time=0.086 ms Nothing weird on my hosts file, I think... xxxxxx ~ # grep -v ^# /etc/hosts 127.0.0.1 localhost localhost.localdomain 176.31.xxx.xx xxxxxx.net ns1.xxxxxx.net ::1 ip6-localhost ip6-loopback feo0::0 ip6-localnet ff00::0 ip6-mcastprefix ff02::1 ip6-allnodes ff02::2 ip6-allrouters ff02::3 ip6-allhosts And ifconfig reports all ok... eth0 Link encap:Ethernet HWaddr e0:69:95:d8:30:a1 inet addr:176.31.xxx.xx Bcast:176.31.108.255 Mask:255.255.255.0 inet6 addr: 2001:41d0:8:xxxx::/64 Scope:Global inet6 addr: 2001:41d0:8:xxxx:x:xx:xx:xx/64 Scope:Global inet6 addr: fe80::e269:95ff:fed8:30a1/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:16916 errors:0 dropped:0 overruns:0 frame:0 TX packets:16914 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:8410679 (8.0 MiB) TX bytes:10539881 (10.0 MiB) Interrupt:28 Base address:0xe000 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:5570 errors:0 dropped:0 overruns:0 frame:0 TX packets:5570 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:744490 (727.0 KiB) TX bytes:744490 (727.0 KiB)