using ULA for 'hidden' v6 devices?

Thu Jan 26 16:45:39 UTC 2012

On Jan 26, 2012, at 7:35 AM, Cameron Byrne wrote:

> 
> On Jan 26, 2012 5:49 AM, "Owen DeLong" <owen at delong.com> wrote:
> >
> >
> > On Jan 26, 2012, at 2:00 AM, George Bonser wrote:
> >
> > >> Use different GUA ranges for internal and external. It's easy enough to
> > >> get an additional prefix.
> > >>
> > >>> As others have mentioned, things like management interfaces on access
> > >> switches, printers, and IP phones would be good candidates to hide with
> > >> ULA.
> > >>
> > >> Or non-advertised, filtered GUA. Works just as well either way.
> > >>
> > >> Owen
> > >>
> > >
> > > If one is obtaining "another" prefix for local addressing, I see no benefit.  I am assuming that anyone that is using ULA is using it for things that don't communicate off the site such as management interfaces of things, etc.  This won't be a subnet you are connecting by VPN to another organization, usually, but even if you do the chances of collision is pretty low if you select your nets properly.  But for the most absolutely paranoid site, I can see some appeal in using ULA in conjunction with DNS64/NAT64 and see them giving the devices internet access via v4.  Not that I agree with the notion, mind you, just that I can see someone looking at that as an appealing solution for some things.  Even if someone managed to get through the NAT device via v4, they would have nothing to talk to on the other side as the other side is all v6.
> > >
> >
> > Even if you don't see an advantage to GUA, can you point to a disadvantage?
> >
> > IMHO, it would be far less wasteful of addressing overall to deprecate fc00::/7 and use unique secondary GUA prefixes for this purpose than to use ULA.
> >
> > If you can't point to some specific advantage of ULA over secondary non-routed GUA prefixes, then, ULA doesn't have a reason to live.
> >
> 
> 1. You don't want to disclose what addresses you are using on your internal network, including to the  rir
> 
Seriously?
> 2. You require or desire an address plan that your rir may consider wasteful.
> 
Have you looked at current IPv6 policies? It's pretty hard to imagine implementing one.
> 3. You don't want to talk to an rir for a variety of personal or business process  reasons
> 
Meh. I have little or no sympathy for this.
> 4.  When troubleshooting both with network engineers familiar with the network as well as tac engineers,  seeing the network for the first time,  ula sticks out like a sore thumb and can lead to some meaningful and clarifying discussions about the devices and flows.
> 
I can see this, but, to me it seems like a double edged sword. Most things that stick out like a sore thumb are inflamed and painful. I don't see this as an exception.
> 5. Routes and packets leak. Filtering at the perimeter? Which perimeter? Mistakes happen. Ula provides a reasonable assumption that the ISP will not route the leaked packets. It is one of many possible layers of security and fail-safes.
> 
Routes only leak if the routes exist on the border routers in the first place. If I were using multiple GUA prefixes and one was intended not to cross the border, I wouldn't feed it to the border routers to begin with. You can't leak what you don't know.

Owen