[GRLUG] Testing a host's IPv6

[Michael Mol]

On Sat, Jan 15, 2011 at 2:41 PM, Bob Kline <bob.kline at gmail.com> wrote:
> Someone mentioned that recent distributions
> come with IPv6 enabled.  How might one verify
> that it is enabled?
>     -- Bob

Actually, I recently blogged how to probe your network for IPv6 hosts,
but here's a slightly expanded version.

Drop to a terminal environment.
Run "ifconfig", to list your operating network interfaces. Here's a
sample, with irrelevant bits stripped out:

eth0      Link encap:Ethernet  HWaddr aa:00:00:dc:00:e7
          inet6 addr: fe80::a800:ff:fedc:e7/64 Scope:Link

lo        Link encap:Local Loopback
          inet6 addr: ::1/128 Scope:Host

Any line where you see "inet6 addr" is an IPv6 address that interface
is listening on. A network interface may have more than one IPv6
address. Here, we see two IPv6 addresses, one on "eth0", and one on
"lo".

eth0's IPv6 line says that its address is fe80::a800:ff:fedc:e7/64,
and that the scope (where that address is valid/meaningful) is "Link".
That means that it's only valid on the local Ethernet segment. (Well,
technically, that means it's valid on the local 802 network segment,
which Ethernet and wifi both fall under, along with things like token
ring and FDDI.)

lo's IPv6 line says that its address is ::1/128, and that its scope is
"Host", which means it's only valid on the local system.

Another interesting thing you can do is probe for IPv6 hosts on your
local network.  On the above system (which happens to be one of my VPS
nodes), I ran the command:

ping6 -I eth0 -c 2 ff02::1

Which means, "Use interface eth0 to send two ICMPv6 echo packets to
the address ff02::1." Address ff02::1 is a multicast address which all
IPv6-enabled network interfaces are supposed to pay attention to. Any
system that sends replies to ICMPv6 echo requests will send an echo
reply to the system that pinged that address.

The result of my ping6 on that VPS node?

PING ff02::1(ff02::1) from fe80::a800:ff:fedc:e7 eth0: 56 data bytes
64 bytes from fe80::a800:ff:fedc:e7: icmp_seq=1 ttl=64 time=0.038 ms
64 bytes from fe80::a800:ff:fe31:4954: icmp_seq=1 ttl=64 time=24.9 ms (DUP!)
64 bytes from fe80::a800:ff:fedc:20: icmp_seq=1 ttl=64 time=29.4 ms (DUP!)

.... snippped ...

64 bytes from fe80::a800:ff:fedc:3e: icmp_seq=1 ttl=64 time=998 ms (DUP!)
64 bytes from fe80::a800:ff:fedc:e7: icmp_seq=2 ttl=64 time=0.038 ms

--- ff02::1 ping statistics ---
2 packets transmitted, 2 received, +86 duplicates, 0% packet loss, time 999ms
rtt min/avg/max/mdev = 0.038/97.517/998.750/141.216 ms

So I know there are at least 86 other NICs on my VPS node's network
whose operating systems are enabled for IPv6, and who respond to
ICMPv6 ECHO packets.

--
:wq

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