ipv6 source address selection
swmike at swm.pp.se
Sat Oct 19 17:12:38 CEST 2013
I'm trying to influence my source address selection. First I thought I'd
figure out how it works by default.
I have a /48. Let's call it 2001:db8:1::/48
I created three /64s on the same LAN with A-bit set so clients would do
SLAAC within these:
Then I set up loopback addresses on my router:
Then I tried pinging each loopback address from a host which has 2
addresses out of each /64. It now picked a source address within the same
/56. I consistently both on a Ubuntu 13.04 and OSX 10.8.5 machine get the
So above means that pinging 2001:db8:1:1fff::1 it would use the :1000:
address, and pinging :2fff::1 would use the :2000::/64 address.
If I ping outside my /48 it will consistently use the last created address
(I tried adding a 4th lan, 8000, and it then uses that one), which I
When I ping :5000: and so on, it will sometimes use the :0000: address and
not the :8000: that is used for the rest of global traffic.
I have nothing /56 or /48 magic in routing table or "ip addrlabel list",
but it still seems to be something special when it comes to the same /48
as the machine has addresses in.
Any help understanding what is going on is appreciated.
Mikael Abrahamsson email: swmike at swm.pp.se
More information about the ipv6-ops