IPv6 basics; connecting via link-local

[Originally posted Mar 18, 2012 4:40 AM by Antti Uitto   [ updated Mar 18, 2012 5:34 AM ]]

In today’s story we are attached to a local area network (LAN) with a bunch of IPv6-enabled hosts. We do not necessarily need to have a valid IPv6 router present, since we are just fooling around in this local segment, pinging each other and testing connections.

IPv6 is a protocol meant serve a worldwide network and it’s numerous hosts. There are however addresses called link-local in each IPv6-enabled host. This link-local address is generated automatically by your computer’s operating system and it is valid for connectivity between hosts that can see each other in L2, even in absence of IPv6 routers. These addresses are also used by IPv6’s Neighbor Discovery Protocol.

Does my host have IPv6?

If your operating system is from this millenia, it should have IPv6 available. But let’s check.

Linux

user@host:~$ ifconfig
eth0      Link encap:Ethernet  HWaddr 00:13:d4:3e:dd:b3  
          inet addr:192.168.1.140  Bcast:192.168.1.255      
          Mask:255.255.255.0          
          inet6 addr: fe80::213:d4ff:fe3e:ddb3/64 Scope:Link
lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host

Mine seems to have. Note that both of my IPv6 addresses are such that they would not help me if I wanted connectivity in the global Internet. They are valid inside my own LAN segment.

Windows

ipconfig

MAC OSX

ifconfig

Pinging IPv6

Ping commands:

Linux ping6  (http://linux.die.net/man/8/ping6)
Windows ping -6 
Mac OSX ping6
Cisco router ping ipv6

Is there anybody out there?

I pinged with my Linux box to my own localhost address

user@host:~$ ping6 ::1
 PING ::1(::1) 56 data bytes
 64 bytes from ::1: icmp_seq=1 ttl=64 time=0.036 ms
 64 bytes from ::1: icmp_seq=2 ttl=64 time=0.044 ms

It works!

Next I will check if I can see any IPv6 neighbors

user@host:~$ ip -6 neighbor
user@host:~$

There was no-one there.

I will attempt to summon other hosts to become visible by pingin to address ff02::1 which is  ip6-allnodes. All other IPv6 hosts should respond to this call.

user@host:~$ ping6 -I eth0 ff02::1
 PING ff02::1(ff02::1) from fe80::213:d4ff:fe3e:ddb3 eth0: 56 data bytes
 64 bytes from fe80::213:d4ff:fe3e:ddb3: icmp_seq=1 ttl=64 time=0.051 ms
 64 bytes from fe80::ba8d:12ff:fe03:474c: icmp_seq=1 ttl=64 time=70.8 ms (DUP!)
 64 bytes from fe80::1636:5ff:fe19:2392: icmp_seq=1 ttl=64 time=204 ms (DUP!)

Note! You will need to insert the name of the interface in the ping command. ( -I eth0 in this case)

After pinging allnodes-address I check again my neighbors:

user@host:~$ ip -6 neigh
 fe80::ba8d:12ff:fe03:474c dev eth0 lladdr b8:8d:12:03:47:4c REACHABLE
 fe80::1636:5ff:fe19:2392 dev eth0 lladdr 14:36:05:19:23:92 STALE
 fe80::a667:6ff:fe87:6b71 dev eth0 lladdr a4:67:06:87:6b:71 STALE

I ping one of them directly using the same syntax:

user@host:~$ ping6 -I eth0 fe80::ba8d:12ff:fe03:474c
 PING fe80::ba8d:12ff:fe03:474c(fe80::ba8d:12ff:fe03:474c) from fe80::213:d4ff:fe3e:ddb3 eth0: 56 data bytes
 64 bytes from fe80::ba8d:12ff:fe03:474c: icmp_seq=1 ttl=64 time=22.9 ms
 64 bytes from fe80::ba8d:12ff:fe03:474c: icmp_seq=2 ttl=64 time=40.9 ms

And the ssh into the neighbor:

user@host:~$ ssh fe80::ba8d:12ff:fe03:474c%eth0
 Password:
 Last login: Sun Mar 18 13:14:22 2012 from host.local
 Another-host:~ ap$
 Another-host:~ ap$

Note!  When connecting with link-local addresses you will need to specify the interface for the connection. In this case it is given as  %eth0  in the end of the neighbors link-local address.

Sources
Carla Schroder: Linux Networking Cookbook
http://en.wikipedia.org/wiki/Link-local_address#IPv6

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