Summary

  • André Grüneberg describes BCIX members exchanging IPv4 reachability through IPv6 next hops without an IPv4 address on the exchange peering LAN.
  • A member using only that mode cannot automatically reach legacy peers. His bridge is a real router, with AS-path handling that the exchange must own explicitly.

The obvious saving at an Internet exchange is one less IPv4 address on a member’s port. The less photogenic bill arrives when that member wants to talk to a peer still using IPv4 next hops. In his RIPE Labs account, BCIX CTO André Grüneberg describes that bill with unusual candour: the middle cannot be wished away by changing a route-server template.

RFC 8950 permits BGP to advertise IPv4 reachability with an IPv6 next hop after the relevant capability is negotiated. Capable bilateral peers can move the IPv4 routes onto their IPv6 session and, once forwarding works, retire the IPv4 session and address on that link. At an IXP, however, a route server shares advertisements among many independent members. A member with only the new mode receives routes only from members able to speak it. The old population does not vanish on the day the first new port is installed.

Grüneberg therefore describes a translator that is a router, not a label converter. It participates on both sides and forwards traffic with next-hop self. That introduces a second operational bargain: its ASN normally appears at the front of the path. In the controlled design he describes, the route server removes that leading AS; route preference also needs tuning so a direct path is not displaced by the bridge. The address saved at the port has created a routing-policy decision in the middle.

His piece says two networks had connected to BCIX without an IPv4 peering-LAN address at publication: V4LESS and the RIPE NCC Authoritative DNS Service. That is a concrete deployment claim, not a count of all members or proof of traffic performance. The missing evidence is a current peer roster and route/forwarding test across both sides of the translator. Such a record would show how far the arrangement scales and where packets actually go.

The overlooked workload is administrative as well as technical. A signup form may insist on an IPv4 field; a configuration generator may omit extended next hop; a looking glass may assume one address family per session. Grüneberg’s useful point is that address conservation changes the work rather than erasing it. Someone must operate the compatibility router, verify the AS path and update the tools that keep the IXP legible.