IPV6 Tricks

Have you ever faced with a situation where you where stuck out of your server due to a IP Address Change, well if you didn't you might one day, let me tell you how IPv6 Saved me. I have several Linux Servers in My Company and Due to some maintenance I needed to change the IP Address on on of them, simple task although it went bad due to a miss spelling on the ifcfg-eth0 file. and like I love to go fast with configuration I did a stupid mistake and restarted the network service well needless to say that as soon as I did that I was left outside, started yelling and spelling out some wired brrrrrrr hmmmm grrrrrrr and all sort of mad words. but then I said to my self hey i am an almost Expert I know Networking, how do I solve this, well the port is still listening on the Ethernet Network so If I had some way of login via ARP or MAC or Other Protocol then I was good to go, and then it pupped out to me IPv6 use in link local address based on MAC address and I have the MAC address of my Linux also I remembered that Linux from Kernel 2.6 is using IPv6 Nativity mean that if i will take the MAC address and convert it to IPv6 link local address FE80:: and do not forget to inverse the 7th bit of the MAC address if you have MAC 1234:5678:1111 0001 0010 now it is 0001 0000 1034:5678:1111 and you add to it FE80:: FE80::1034:5678:1111 --> TADA then I will be able to ping it and log in from one of my other servers so that is what I did and there you go a rescue backdoor to your network when your IPv4 network is down. also you could login from remote if you set on your Cisco a 6to4 tunnel, but that is for next article, leave the good stuff for later :-)