Oops--I did confuse them. Apologies. Time to buy another batch of 800-page IPv6 tomes to put on a shelf and eventually read. I guess I'm the reason we haven't switched to IPv6 yet. ;)
-A On Fri, Jun 19, 2026 at 1:48 PM Gary Sparkes <[email protected]> wrote: > ULA is the equivalent of RFC1918, effectively. FC00::/7 > > > > You’re thinking of link-local addresses which are the fe80 addresses. > Those are autogenerated. ULA is assigned however you want – SLAAC, DHCPv6, > static, etc…. RFC1918 equivalent. > > > > Nominally, you’d almost never think about link-local. > > > > You essentially have all of fc00::/7 to utilize as you wish. > > > > So, for you, I suppose, you could do FC00:0:22:XXXX::/64 > > > > 22nd state, XXXX being vlan ID or some other identifier or whatever you > want (servers could be FC00:0:22:1::/64 and workstations FC00:0:22:2::/64 > and so on – feel free to be creative! You have FC00::/32 through > FC00:3E8::/32 to play around in! With /48’s I like to do > PRE:FIX:HERE:VLANID::/64) > > > > Including the office number, so you could do FC00:22:0:1 (the 0 between > the 22 and 1 is the office number, second the network/vlan identifier, > whatever – you can be creative and as long or compact as you want here). > > > > So let’s say you have FC00:22:0:1::1 – okay, that’s a router! > FC00:22:0:2:SLAA:CASS:IGNE:DAUTOCONF – sweet that’s a workstation (SLAAC > for simplicity sake, DHCPv6 can also be an option, but a bit more to > configure/maintain). FC00:22:0:1::250 – that’s the linux server! > > > > Okay, so now your linux server is FC00:22:0:1::250, still simple enough. > And any firewall logs with that info will immediately tell you right where > it is and what network it’s on, etc. > > > > Then with NPT, you’re mapping provider prefix aaand you’re right where you > were with V4, including needing to update DNS in failover. > > > > Now you just change the provider prefix portion instead of the whole IP > address. The ::250 will stay the same on either provider externally. NPT > will just convert say, 1234:5678:1234:5678::/64 to FC00:22:0:1::/64 at the > edge, and vice versa. So your linux server would be 1234:5678:1234:5678::250 > > > > You never want to hardcode link-local addressing, that’s all entirely > autonomous and is used for a variety of things, but that’s out of scope > here. > > > > > > *From:* Aaron C. de Bruyn <[email protected]> > *Sent:* Friday, June 19, 2026 4:24 PM > *To:* Gary Sparkes <[email protected]> > *Cc:* North American Network Operators Group <[email protected]>; > Marco Moock <[email protected]> > *Subject:* Re: IPv4 flag day > > > > On Fri, Jun 19, 2026 at 1:03 PM Gary Sparkes <[email protected]> > wrote: > > The clean path would be NPTv6 with ULA for the same exact setup. > > It would slot in and work identically to how the IPv4 deployment is today. > > Instead of RFC1918, you have ULA addressing. Same concept. > > Except with NPTv6 you're doing 1:1 and eliminate PAT. > > Of course, if you're single provider, might as well just use prefix > delegation, NPT's real shine is the multi-WAN scenario with no upstream > routing protocol that sparked off a lot of discussion. > > As to changing providers when using prefix delegation, most stuff can > auto-update itself, but otherwise it's a simple find/replace exercise in > documentation and records when your provider prefix changes as the last > half of the address is entirely stable, and the first half is (mostly) > provider. > > > > Maybe I need to do a bit more digging as I'm not an expert at IPv6--but > aren't ULA addresses basically randomly assigned to hosts based on their > NIC HW address and a few other things? > > > > A short example from a very large client I manage: > > They use IPv4 10/8 > > The next octet is allocated for the state the office is located in "plus > 100". So if they open an office in Alabama (22nd state to join the union), > it's gonna be 10.122/16. > > The third octet is assigned sequentially. The first office opened in > Alabama is 10.122.0.0/24. > > The last octet is static. Router at .254, linux server at .250, Windows > (ugh) RDP server at .249, workstations are DHCP between .100 and .199, > etc... > > > > You can give me nearly any IP from this client and I know the device. > > But ULA gives me: fe80::ae1f:6bff:feb0:3c98/64 > > > > What even is that? Their router? A Windows box? > > > > Hard-code the address to fe80::122:00000:250/64 (just to know it's a linux > server in Alabama) and then set up NPTv6...and update a *ton* of DNS info > so the rest of the world can easily get to the correct machines? > > > > Again, I'm having to renumber somewhere--either update a bunch of DNS or > update a bunch of internal machines when I change ISPs or have a fail-over. > > > > At least that's what it always seemed like to me after going through all > the 800-page IPv6 tomes over the years. ;) > > > > -A > _______________________________________________ NANOG mailing list https://lists.nanog.org/archives/list/[email protected]/message/RUN3LBYYAY77TYVEMVM6M4456E72YF2C/
