IPv6 Fragmentation and the DNS

In this episode of PING, APNIC’s Chief Scientist Geoff Huston discusses the change in IP packet fragmentation behaviour adopted by IPv6, and the implications of a change in IETF “Normative Language” regarding use of IPv6 in the DNS. IPv4 arguably succeeds over so many variant underlying links and networks because it’s highly adaptable to fragmentation in the path. IPv6 has a proscriptive requirement that only the end hosts fragment, which limits how intermediate systems can handle IPv6 data in flight. In the DNS, increasing complexity from things like DNSSEC mean the the DNS packet sizes are getting larger and larger, which risks invoking the IPv6 fragmentation behaviour in UDP. This has consequences for the reliability and timeliness of the DNS service. For this reason, a revision of the IETF normative language (the use of capitalised MUST MAY SHOULD and MUST NOT) directing how IPv6 integrates into the DNS service in deployment has risks. Geoff argues for a “first, do no harm” approach to this kind of IETF document. Read more about IPv6, Fragmentation, the DNS and Geoff’s measurements on the APNIC Blog and APNIC Labs.