Default gateway on different net

[bz=lists at zabbadoz.net]

On Fri, 24 Sep 2010, Hiroki Sato wrote:

> Lasse Brandt <lasse at bitmand.com> wrote
>  in <6BE964C4-0838-4DA6-9278-12C620CA1EE1 at bitmand.com>:
>
> la> 1) Is the hosting provider actually forcing me to do something "bad"
> la> og plain wrong?
>
> In that situation normally you get an IP address in the /59 network
> to communicate with the gateway router from ISP.  An IP address in
> your /64 network cannot directly communicate with an address in /59.
>
> If you do not have the /59 address, I think using link-local address
> is the easiest way.  As long as the gateway works correctly, you can
> get its link-local address by using the following command:
>
> % ping6 ff02::2%re0
> PING6(56=40+8+8 bytes) fe80::XXXX:XXXX:XXXX:XXXX%re0 --> ff02::2%re0
> 16 bytes from fe80::YYYY:YYYY:YYYY:YYYY%re0, icmp_seq=0 hlim=64 time=0.525 ms
> 16 bytes from fe80::YYYY:YYYY:YYYY:YYYY%re0, icmp_seq=1 hlim=64 time=0.312 ms
> ^C
>
> Note that "XXXX:.." is your address on re0, and "YYYY:.." is the
> gateway's.  You do not need any configuration like assigning
> 2a01:... address into re0 or static routes before performing this
> ping.  At least one router replies to this and displays its link-local
> address.
>
> After that, you can add the default route to it:
>
> # route add -inet6 default fe80::YYYY:YYYY:YYYY:YYYY%re0
>
> and configure your /64 address (2a01:...) to re0.

The drawback with that is if the hosting provider changes the interface
of your gateway, moves you to a different router, ... your default route
stops working.


Imho you do not get an address out of the /59 and to my memory the
usually offered linux doesn't really care and even in the IPv4 happily
arped for gateways on unconnected subnets happily, so I would assume
it's probably the same for nd6 with that?

What they usually do is to give you a pvlan (a private, per customer,
vlan) so you could pick any address of the /59, which may or may not
include your /64.  As you do not want to put the /59 on-link though
you may use the /64 or a /126 which includes the address of the router.
The obvious drawback with that is that you have to make sure that the
address isn't used with source address seclection to not run into
troubles as it wouldn't be reachable from outside but only used for
the kernel to properly find the on-link gateway.

I guess the link-local one and risking a "service interruption" in
case of router (interface) changes might be the most elegant one.
One could even use a simple script that would update things
automatically if needed.

/bz

PS: there is a private email in flight as well, as we know someone who
     has a working FreeBSD IPv6 setup at that hosting company.

-- 
Bjoern A. Zeeb                              Welcome a new stage of life.