[GRLUG] Testing a host's IPv6

[Michael Mol]

On Sat, Jan 15, 2011 at 3:16 PM, Adam Tauno Williams
<awilliam at whitemice.org> wrote:
> On Sat, 2011-01-15 at 15:03 -0500, Michael Mol wrote:
>> 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.)
>
> Actually, the link-local address is valid on any IPv6 link; even
> point-to-point links like PPP or HDLC.

I suppose it may be technically valid, but link-local IP addresses are
only guaranteed to be unique in Link scope. If you have multiple
non-bridged 802 networks (say, wired and wifi, and they're not
directly connected), and a machine has a NIC on each network, the same
link-local address may exist on both addresses, but be associated with
different machines.

So, really, you shouldn't route link-local scope packets. There's a
site-local scope which seems similar in purpose to RFC 1918 addresses,
but that's deprecated with no specified replacement I'm aware of.


-- 
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