Addressing plan exercise for our IPv6 course

Owen DeLong owen at
Sat Jul 24 12:48:50 CDT 2010

On Jul 24, 2010, at 9:23 AM, Karl Auer wrote:

> On Sat, 2010-07-24 at 08:50 -0700, Matthew Kaufman wrote:
>> Even if all your hosts end up with external connectivity that works, the odds 
>> that they can reliably talk to each other is low.
> I hope I'm not taking the above quote out of context, but why do you
> think this? How does the fact that interfaces on your host may have more
> than one public address translate into low odds that they can talk to
> each other?
> The only thing I can think of is that if an interface in your network
> has a public address from only one provider, and another interface in
> your network has a public address only from another provider, then the
> connection will go out through one provider and back in from the other,
> which would be less than optimal. On the other hand, there is no reason
> to think this would be particularly unreliable, and if such a situation
> existed it would either indicate a fault or be what you actually wanted.
I would think even that would be unlikely as the border routers would
most likely know routes to both sets of internal addresses and worst
case, the packets should hairpin inside the border router rather than
being forwarded to the external providers.

Ideally, this hairpinning should be designed to occur prior to reaching
the firewall, or, the firewall(s) must have rulesets to enable such.
However, either solution is easily implemented in most topologies.


More information about the NANOG mailing list