Moin, I agree with this point, and will happily remove this paragraph in place of only stating the reference to min-MTU/TCP_MAXSEG (which, iirc, the draft explicitly notes further below) and RFC9715.
However, the above is a vocal counter argument against IPv6 for DNS, and as such was strongly required during an earlier discussion... So, as an author, I am currently receiving a bit of mixed signals from the group here. With best regards, Tobias On Tue, 2025-08-05 at 11:30 +1000, Mark Andrews wrote: > draft-ietf-dnsop-3901bis-03 states: > > If the requesting resolver is unable to process fragments, or > if > fragments are filtered on-path, resolution will fail over UDP. > These issues are more prevalent for IPv6, as it no longer > allows > on-path hosts to fragment packets. Therefore, working Path MTU > Discovery (PMTUD) is essential for IPv6 DNS-over-UDP packets to > be > fragmented to a size that allows them to traverse all segments > on > a path. > > This is not factually correct. There is NO requirement to perform > PMTUD > at all in a DNS server over IPv6. For UDP you just fragment at > network > MTU in the sending node at network MTU. This can be achieved by > using > IPV6_USE_MIN_MTU=1 socket option from RFC 3542 or using an interface > that > is configured with a MTU that matches the network MTU. For TCP you > use > the socket option TCP_MAXSEG to set the MSS to the network MTU. > > Both of these options have been used for years in nameservers and > avoid > response losses caused by attempting PMTUD itself. > > -- > Mark Andrews, ISC > 1 Seymour St., Dundas Valley, NSW 2117, Australia > PHONE: +61 2 9871 4742 INTERNET: [email protected] > > _______________________________________________ > DNSOP mailing list -- [email protected] > To unsubscribe send an email to [email protected] -- Dr.-Ing. Tobias Fiebig T +31 616 80 98 99 M [email protected] Pronouns: he/him/his _______________________________________________ DNSOP mailing list -- [email protected] To unsubscribe send an email to [email protected]
