Netcat testing 3306 tcp connexion

gistfile1.txt

[root@centos mysql]# nc -vz localhost 3306
nc: connect to localhost port 3306 (tcp) failed: Connection refused
Connection to localhost 3306 port [tcp/mysql] succeeded!


The reason is the first connection is against ::1 (IPv6), and the second to 127.0.0.1.
This could be seen with: tcpdump -i lo -n


[root@centos mysql]# grep localhost /etc/hosts
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6


iptraf doesn't show this correctly, hidding the ipv6 connection under the ipv4 connection