On 19 Apr 2021, at 12:40, Peter van Dijk <peter.van.d...@powerdns.com> wrote:
> This note on statelessness is good, but I don't think it should be tied to > IPv6. Packets get lost in IPv4 too, especially when they are big, and even if > such evens trigger a report in the form of an ICMP message, the same > lack-of-state problem applies. In IPv4, datagrams that need to be transmitted over a link with an MTU is too low are fragmented by the router attached to the link, assuming DF=0. There is no signal sent back to the source in that case. In IPv6 that doesn't happen. In the v4 case a large DNS message (large enough to require fragmentation along the path) can be transmitted without the source having to retain any state. That's not true in v6. So I think the v4 and v6 cases are different. That's why I attached that comment to the v6 case. DNS messages can be lost in both v4 and v6 for a variety of other reasons, I agree. > https://datatracker.ietf.org/doc/draft-ietf-dnsop-avoid-fragmentation/ even > proposes setting DONTFRAG socket options, and some servers out there already > send IPv4 replies with the DF bit set (the two I can verify immediately are > OpenDNS, and whatever is running on the router my provider gave me, but most > likely there are others too). Setting DF=1 does seem like it would avoid the differences I was trying to allude to above, I agree. With DF=1 fragmentation (or not-fragmentation) is just another reason for a packet to get dropped. Joe _______________________________________________ DNSOP mailing list DNSOP@ietf.org https://www.ietf.org/mailman/listinfo/dnsop
