Extra inet6 addr's on sixxs iface with Scope:Link ?
Shadow Hawkins on Wednesday, 15 October 2008 04:20:59
I've tried searching, but I don't exactly have easy search terms to work with...
I just got a SixXS tunnel setup and configured using aiccu under Ubuntu Linux 8.04. I see a new interface called "sixxs":
sixxs Link encap:IPv6-in-IPv4
inet6 addr: fe80::600e:acf0/64 Scope:Link
inet6 addr: 2001:4978:f:xxx::2/64 Scope:Global
inet6 addr: fe80::c0a8:5201/64 Scope:Link
I'm curious to know what the 2 extra inet6 addr's are for with "Scope:Link".
Thanks!
Extra inet6 addr's on sixxs iface with Scope:Link ?
Jeroen Massar on Wednesday, 15 October 2008 11:09:41
This is a Linux-specific way of generating link-locals. It is a bit wrong in one sense, but correct in another. Translate them and you will understand how they are generated.
I cheat a bit here, by converting the address to a '6to4' format and then converting them, you can also just take the last 32bits and translate those though:
fe80::600e:acf0/64 -> 2002:600e:acf0::
$ ipv6calc -i 2002:600e:acf0::
No input type specified, try autodetection...found type: ipv6addr
No output type specified, try autodetection...found type: ipv6addr
Address type: unicast, 6to4, global-unicast, productive
Address type is 6to4 and included IPv4 address is: 96.14.172.240
....
This is the IPv4 address of one of the interfaces on your host, most likely the Internet facing one.
fe80::c0a8:5201/64 -> 2002:c0a8:5201::
$ ipv6calc -i 2002:c0a8:5201::
No input type specified, try autodetection...found type: ipv6addr
No output type specified, try autodetection...found type: ipv6addr
Address type: unicast, 6to4, global-unicast, productive
Address type is 6to4 and included IPv4 address is: 192.168.82.1
....
And that is most likely the one on your local interface, RFC1918, thus behind your NAT.
The trick here is that you haven't configured the "local" part of the tunnel device (the sixxs interface), thus the kernel can expect proto-41 packets targeted at both your IPv4 addresses, which is why it generates link-locals for both.
Extra inet6 addr's on sixxs iface with Scope:Link ?
Shadow Hawkins on Thursday, 16 October 2008 01:38:16
Thanks for the insightful answer!
I thought maybe they were MAC addresses, but couldn't find any matches that way. I hadn't consider other IP addresses.
They way you mentioned "the trick" about not having configured the "local" part of the tunnel device... Is this something that I should do?
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