A Farewell to ARPs - IPv6 resolved gateways#

Remco van Mook

• Why: IPv6-only fabrics with native IPv4 reachability is a live design problem for DC/WAN interconnect. This proposes a clean mechanism to give IPv4-capable hosts on an IPv6-only network a working IPv4 default gateway without ARP, tunnels, or translation — complementary to RFC 8950 (IPv4 NLRI with IPv6 next-hop).
• What: A draft I-D requesting 192.0.0.11/32 from the IANA IPv4 special-purpose registry. The address is a signal: hosts configured with it as their IPv4 default gateway resolve the gateway's link-layer address from the IPv6 default gateway learned via RA/ND — reusing the IPv6 neighbor cache instead of running ARP. IPv4 packets remain native and unaltered; no IPv4 subnets, no tunneling, no NAT.
• How: The host treats the gateway IP as a pure identifier for "use the IPv6 gateway's L2"; working code exists in Linux user space (kernel 5.2+) using rtnetlink to track the IPv6 gateway. A transitional deployment — DHCP-assigned /32 address plus a host route for 192.0.0.11 with the address answered on router interfaces — is essentially what some hosting providers (Hetzner-style) already do.
• Where applicable: General technique for IPv6-only datacenters and hosts; cleanly it needs OS network-stack support (currently user-space/known-config), but the transitional method is deployable today. Aligns with ongoing IETF v4-via-v6 work; the presenter was soliciting review of the draft and code.