RFC8950: Announce IPv4 with an IPv6 next-hop (anuragbhatia.com)
92 points by porridgeraisin 8 hours ago
billpg 8 minutes ago
Shameless plug: https://billpg.com/sixgate/
(Short version: IPv6-only networks can provide a gateway for IPv4-only clients and advertise it via reverse DNS.)
SixGate has an interesting contrast with this RFC. RFC8950 removes IPv4 from the network core while preserving IPv4 reachability, whereas SixGate removes IPv4 from the service side while preserving reachability for IPv4-only clients.
In both cases, IPv4 survives as a compatibility layer rather than a fundamental requirement. The difference is that RFC8950 is aimed at network operators, while SixGate is aimed at the last remaining IPv4-only users.
In both cases, the goal is the same. Turn IPv4 from a requirement into an optional compatibility feature.
Isomer 5 hours ago
I don't understand why you can't have any protocol that can (potentially recursively) resolve to a layer 2 address as a next hop.
v4 route with v6 next hop? Seems reasonable. v6 route with v4 next hop? Why not? v4/v6 route with a mac address as a next hop? Trivial. v4/v6 route with a DNS next hop? Could be recursively resolved to a v4/v6 address, and then potentially recursively resolved to a MAC address. I wouldn't recommend it, but sure. v4/v6 route with a netbeui name as a next hop? You appear to be mad, but I'm not going to be the one to stand in your way.
throw0101c 5 hours ago
> I don't understand why you can't have any protocol that can (potentially recursively) resolve to a layer 2 address as a next hop.
Which Layer 2? Ethernet? Token Ring? Infiniband? ATM? Fibre Channel?
Both IPv4 and IPv6 were created when there were multiple Layer 2 protocols in use. That's why where was a completely different protocol to handle Layer 2 to 3 mappings (often itself referred to as a Layer "2.5" one):
q3k 5 hours ago
That's basically MP-BGP! Your dream is real.
(Keep in mind that the setup described here has work for years now.)
imoverclocked 44 minutes ago
> R1 & R2 are IPv6 only with no IPv4 anywhere on their interfaces (but carry IPv4 routes in their table)
… proceeds to traceroute with IPv4 addresses showing up for each router…
It’s neat but still requires IPv4 to be configured on the router? What am I missing?
Sesse__ 23 minutes ago
You still need at least one IPv4 address somewhere if you want to send ICMP back, yes. (Typically a loopback, i.e., something not connected to a specific interface. Routers use loopback interfaces for rather different purposes than a Linux workstation.) But you don't need to set up an IPv4 address on every interface, so you don't need a linknet plan.
You can also forego the IPv4 addresses entirely, but then traceroute (and presumably also stuff like Path MTU Discovery; have consistent MTUs!) won't work. traceroute is often broken for entirely different reasons, though.
petecooper 6 hours ago
gopalv 2 hours ago
> They still do things the old way but Backbone can run IPv6 only at its core.
This would turn an internal IPv4 into an externally routed IPv6, which is a neat trick which would replace all the NAT madness that we do run today.
I'd like nothing more than the ability to run ipv4 internally indefinitely, especially with things like mesh networks where the ACLs are carried over from ages ago (2018 doesn't feel that long ago, but it is).
Most of the time I don't even need a route to a direct connection, I just need legible flow logs out of a kubernetes platform.
Alifatisk 7 hours ago
I guess the point with this to facilitate usage of IPv6.
Sesse__ 6 hours ago
More like, the point is to facilitate turning off IPv4. It's much nicer to manage a single-stacked backbone, but you still need IPv4 out in the edges somehow (for many cases, anyway). I guess this is another way to do that.
Heck, I would be happy if I could remove some IPv4 linknets from my IS-IS, myself, and just route using IPv6 link-local nexthops…
throw0101c 4 hours ago
> I guess the point with this to facilitate usage of IPv6.
See §6, "Usage Examples": IPv4 over IPv6 Core, IPv4 VPN Unicast over IPv6 Core, IPv4 VPN Multicast over IPv6 Core.
* https://datatracker.ietf.org/doc/html/rfc8950#name-usage-exa...
So it's to facilitate legacy IPv4 usage when the rest of your infrastructure is IPv6.
simoncion 6 hours ago
The Abstract and Introduction sections of the RFC [0] explain what the point of this is. The "Changes Compared to RFC 5549" section is especially good reading, as it both alerts you to the fact that this is an update to a seventeen year old RFC and explains what changed in the update.
Polizeiposaune 5 hours ago
It's to facilitate use of IPv4 in an IPv6-mostly network.
miyuru 5 hours ago
Multiple ISPs in my country have already deployed IPv6 with NAT64 support, and with CLAT support now available, I think IPv6-only networks will be the next step for most ISPs.
yayachiken 5 hours ago
IPv6 mostly (RFC 8925) is a rather nice migration option.
Modern operating systems will gladly do CLAT, and old operating systems (or fussy users) can still get their IPv4 by just ignoring the new DHCPv4 option. But admins can finally stop keeping an IPv4 around for every potential client as most applications and users really don't care.
ianburrell 5 hours ago
There is also MAP-T which basically does CGNAT with IPv6-only provider network. The local network gets IPv4, the router translates to IPv6 which goes to stateless IPv4 NAT proxy. The advantage is that the proxy is stateless unlike CGNAT. The downside is requires custom code on the router.
q3k 5 hours ago
It's also just nice to not need numbered point-to-point links (ie. just use IPv6 LL).
(this is one of those things that's really magical with OSPv3 - it just runs on IPv6 LL addresses, no need to set anything up other than set the link to be within some area and it just works! well, as much as they do with OSPF anyway.)
Polizeiposaune 2 hours ago
A router still needs a non-link-local address in order to be able to send ICMP errors off-link -- which you're going to want if you want sensible output from traceroute..
frantathefranta an hour ago
asdfsa32 6 hours ago
A few more RFCs, a few more IP over IP bandaid, a few more extensions, and we will get there. By God IPv6 is a stain in the history of computer science.
IPv6 should have really just worked like NAT/IP over IP on IPv4 hardware and fast path on IPv6 hardware. But instead we got a monster that keeps growing with things like NAT64, 4over6, DS-Lite, MAP-E, and now BGP stopgaps and a growing
https://en.wikipedia.org/wiki/List_of_IPv6_transition_mechan...
wredcoll 6 hours ago
> IPv6 should have really just worked like NAT/IP over IP on IPv4 hardware
This literally exists. There's no need for it to be part of the original specification because it's a completely separate concept.
There's nothing wrong with ipv6 other than the general human desire to not change things that "work" and for people who are currently powerful because they own a bunch of ipv4 to resist changes.
superchicken099 4 hours ago
If your solution is that “if everyone just used IPv6 we wouldn’t have this problem” then it’s not a solution. Standards like USB, Wi-Fi, HDMI, DP, etc. are so successful because they are by out-of-the-box backwards compatible with their predecessors.
orangeboats 4 hours ago
tredre3 5 hours ago
> There's nothing wrong with ipv6 other than [long list of human things]
The unfortunate reality is that technology exists to serve us. If humans don't want to use it, it means that your technology is wrong. End of story. It doesn't matter if you (or any of us) think it's elegant and beautifully designed.
orangeboats 4 hours ago
asdfsa32 5 hours ago
> This literally exists. There's no need for it to be part of the original specification because it's a completely separate concept.
By that token, IPv6 never had to exist at all then, but we know that is completely missing the point.
IPv6 is a privacy nightmare without privacy extensions. It is designed with "a stupid desire to pretend we can boil the ocean".
Close to 3 decades and we are barely scraping 50%: https://stats.labs.apnic.net/ipv6/
boredatoms 5 hours ago
craftkiller 3 hours ago
cyberax 4 hours ago
> There's nothing wrong with ipv6
Sweet summer child...
There's EVERYTHING wrong with IPv6. It's a recursively bad protocol. From the basic header design (extension headers, wtf) to the "human management" layer ("why should we deploy IPv6 if it actively _breaks_ stuff?").
As an example, try to design a standards-compliant IPv6 network where you can reliably print from an Android phone if your Internet connection goes down and the router withdraws the prefix. It's trivial with IPv4 and _impossible_ with IPv6.
craftkiller 3 hours ago
adrian_b 3 hours ago
icedchai 2 hours ago
throwawaysoxjje 3 hours ago
q3k 5 hours ago
This isn't one of those. It's for ISPs who run a native IPv6 backbone and want to exchange and route IPv4 traffic without setting up IPv4 addressing.
asdfsa32 3 hours ago
It is a network. No part of it is exactly a surprise. But 3 decades in, we are still getting there. Almost 50% any year from now!