Re: Splitting /64 over Multiple Gateway Interfaces in rtadvd

On Mon, Mar 21, 2005 at 03:20:45PM -0600, eric wrote:
| I'm using rtadvd(8) for stateless configuration of machines behind a
| dual-legged OpenBSD router. I've been allocated a /64 from he.net and have
| everything working fine when using a single-leg configuration of the
| router...
|
| fxp0:\
|         :raflags#0:addrs#1:addr="2001:470:1F01:x::":prefixlen#64:
|
| fxp0 has an ipv6 address if 2001:470:1F01:x::1

Why are you using a rtadvd.conf(5) ? The manpage clearly states :

     As described in rtadvd(8), you do not have to set this configuration
file
     up at all, unless you need some special configurations.  You may even
     omit the file as a whole.  In such cases, the rtadvd daemon will
automat-
     ically configure itself using default values specified in the specifica-
     tion.

When you configure fxp0 with 2001:470:1f01:x::1 and start rtadvd on
fxp0, it will, by default, use the prefix and prefixlen that are
specified on your interface.

| However, when I try and split this network up over seperate interfaces,
I've
| tried leaving the /64 undivided and numberd tx0 (the second interface) as
| 2001:470:1F01:x::2 and changed "fxp0" in my /etc/rtadvd.conf to "default"
|
| This doesn't seem to work; I can't get a stateless address assigned.

What exactly is it that you're trying to accomplish ? As Jeroen
pointed out, he.net should give you a /48 if you require more then one
subnet. The second leg on your router should have IPv6, right ? That's
in a completely different network, right ? If so (and note that I've
made some assumptions you have not clarified in your original
message), you should use a different subnet for the second leg. For
stateless autoconfiguration, that would be at least two /64's,
indicating that you need at least a /63 (or two /64 allocations).

You could use one /64, split it up into more, smaller networks (say
2 /65's or 65.536 /80's) and configure each host with it's own unique
address.

This is, however, not recommend, not easy to administer, not elegant
and surely not the best way to do this. But it will be a lot of work
and it will (should) probably work, if done correctly.

| Will I need to split my /64 into two halves? If so, can anyone recommend
| pointers to learning how to do that (I'm not sure if /64 == 2 /65's, etc).

In a sense, 2 /65's are a /64, but you can't use rtadvd on a link with
a /65. Stateless autoconfiguration uses eui-64 (or some
privacy-enabled solution). This requires at least 64 bits for the host
part.

| I could check my copy of TCP/IP illustrated, alas it is in storage and
| tucked away unreachable :-\

I doubt your copy of TCP/IP illustrated will help you in this respect.
Although it's an extremely good reference for IPv4, it has little to
tell about IPv6.

Please let us know what it is you want to do, in stead of how you are
trying to work it out. There may be a better solution to your problem.

Cheers,

Paul 'WEiRD' de Weerd

--
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