Are IPv6-only IXPs coming?

This is part of a series focusing on the presentations from the Netnod Meeting 2025. Each blogpost aims to summarise the key points from the presentation and provides link for readers who want to know more.

Up until recently, before RFC5549 was published, you had to use IPv4 addresses to announce IPv4 address space at an IXP. This is no longer the case. So what stands in the way of IPv6-only IXPs?

In technical terms, nothing. IPv6 ND replaces ARP, one IPv4 address is necessary for loopback, but the remaining IPv4 address space could then be used for revenue generating networks. 

One issue with IPv4 is the smaller prefixes in use. For example both LINX and France-IX have had to renumber to increase the number space to accommodate customers. 

The presentation suggested that if you have to renumber, do it “one final time”, by renumbering to IPv6.

Currently, the NIX.cz exchange is testing RFC8950 (the updated version of RFC5549) in their FENIX subnet, and several members have connected. TREX is also testing the same concept at their IXP in Tampere, and their brand new IXP in Turku, which has been IPv6-only from day one.

Euro-IX is working on best practices for adopting RFC8950 at IXPs, in a working group which is currently co-chaired by Aleksi. 

There are some challenges, though, which have to be addressed going forward. Interoperability has not been tested much in practical scenarios. And looking-glass support is near non-existent. In addition, there are IBGP next-hop and ICMP unreachable quirks which need to be handled. 

If you are interested in participating or contributing to the Euro-IX working group, see https://github.com/euro-ix/rfc8950-ixp.

You can watch Aleksi’s presentation from the Netnod Meeting 2025 here and see the slides here.