15.2. Pinging Link Local IPv6 Hosts

Problem

You want to start with the basics—testing your IPv6 connectivity with ping. Can you even do this?

Solution

Of course you can, with the ping6 command, which should be included in all modern Linux distributions. This is how you ping6 localhost, and your Link Local addresses:

	$ ping6 -c2 ::1
	PING ::1(::1) 56 data bytes
	64 bytes from ::1: icmp_seq=1 ttl=64 time=0.045 ms
	64 bytes from ::1: icmp_seq=2 ttl=64 time=0.048 ms
	--- ::1 ping statistics --
	2 packets transmitted, 2 received, 0% packet loss, time 1002ms
	rtt min/avg/max/mdev = 0.045/0.046/0.048/0.007 ms

	$ ping6 -c2 -I eth0 fe80::203:6dff:fe00:83cf
	PING fe80::203:6dff:fe00:83cf(fe80::203:6dff:fe00:83cf) from fe80::203:6dff:fe00:83cf
	eth0: 56 data bytes
	64 bytes from fe80::203:6dff:fe00:83cf: icmp_seq=1 ttl=64 time=0.046 ms
	64 bytes from fe80::203:6dff:fe00:83cf: icmp_seq=2 ttl=64 time=0.051 ms

	--- fe80::203:6dff:fe00:83cf ping statistics --
	2 packets transmitted, 2 received, 0% packet loss, time 999ms
	rtt min/avg/max/mdev = 0.046/0.048/0.051/0.007 ms

When you ping6 the link local address, you must specify your network interface with the -I switch, even if you have only a single interface on your system. If you don't do this, you'll get a "connect: Invalid argument" error.

Now, how about pinging other hosts on your LAN? First, you must discover them by pinging the Link Local Multicast address:

	$ ping6 -I eth1 ff02::1
	PING ff02::1(ff02::1) from fe80::203:6dff:fe00:83cf eth0: 56 data bytes
	64 bytes from fe80::203:6dff:fe00:83cf: icmp_seq=1 ttl=64 time=0.049 ms
	64 bytes from fe80::214:2aff:fe54:67d6: icmp_seq=1 ttl=64 time=2.45 ms (DUP!)
	64 bytes from fe80::20d:b9ff:fe05:25b4: icmp_seq=1 ttl=64 time=9.68 ms (DUP!)
	[...]

Keep going until you see the same addresses repeating. ping6 helps you by shouting (DUP!). Now you can ping6 them:

	$ ping6 -I eth0 fe80::214:2aff:fe54:67d6

Now you know that your IPv6 Link Local addresses work.

Discussion

How do you know what your Link Local address is? ifconfig tells you:

	$ /sbin/ifconfig
	eth0       Link encap:Ethernet HWaddr 00:03:6D:00:83:CF
	           inet addr:192.168.1.10 Bcast:192.168.1.255 Mask:255.255.255.0
	           inet6 addr: fe80::203:6dff:fe00:83cf/64 Scope:Link
	           UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
	           [...]

See Also