Ever notice that your 6in4 (sit) tunnels on GNU/Linux all have a ton of weird-looking link-local addresses attached to them?

sit2      Link encap:IPv6-in-IPv4  
          inet6 addr: fe80::a03:71e/64 Scope:Link
          inet6 addr: 2001:4830:122d:ffff::2/126 Scope:Global
          inet6 addr: fe80::a03:fe0b/64 Scope:Link
          inet6 addr: fe80::a03:fe1c/64 Scope:Link
          inet6 addr: fe80::a03:fe11/64 Scope:Link
          inet6 addr: fe80::a03:405/64 Scope:Link
          inet6 addr: fe80::a03:fe02/64 Scope:Link
          inet6 addr: fe80::a03:7fa/64 Scope:Link
          inet6 addr: fe80::4bb5:4d73/64 Scope:Link
          inet6 addr: fe80::a03:fd06/64 Scope:Link
          inet6 addr: fe80::a03:5fe/64 Scope:Link
          inet6 addr: fe80::a03:fe07/64 Scope:Link
          UP POINTOPOINT RUNNING NOARP  MTU:1280  Metric:1
          RX packets:83817047 errors:0 dropped:0 overruns:0 frame:0
          TX packets:49313462 errors:86 dropped:0 overruns:0 carrier:86
          collisions:0 txqueuelen:0 
          RX bytes:2897105421 (2.6 GiB)  TX bytes:776361358 (740.3 MiB)

Yeah, like that.

The last four bytes of each address is an IPv4 address attached (or was attached) to another interface on the box.  Let's break down the above example:

fe80::a03:71e/64 -> 10.3.7.30 (eth1.2)
fe80::a03:fe0b/64 -> 10.3.254.11 (been gone for awhile)
fe80::a03:fe1c/64 -> 10.3.254.28 (tun4)
[...]
fe80::4bb5:4d73/64 -> 75.181.77.115 (used to be on eth0)

I think eth0 used to have 75.181.77.115 about a year ago.  It looks like these LL addresses are stored somewhere, and reused over and over again.  I suppose it makes sense - LL addresses only need be unique per link.

I haven't been able to find any hard documentation on this, though, so I'm just guessing…

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