Paul,
I think this might be a little easier for people to parse, and I think it covers everything in yours; R3. UDP responders should compose response datagrams whose size does not exceed the requestor's offered buffer size (EDNS bufsize) or the interface MTU, the route MTU, or the path MTU, if any are known. - If the path MTU can be reliably discovered, then such discovery SHOULD be attempted, and the result used. - For IPv6, an interface MTU other than 1500 bytes should be advertised in a Router Advertisement [RFC4861]. - If none of the MTUs are known, a default of 1500 bytes should be assumed. Further, the MTU should be reduced to account for packetization by the UDP and IP/IPv6 layers, which might add as many as 100 bytes, resulting in the RECOMMENDED 1400 Bytes. R5. UDP requestors should set the requestor's offered buffer size (EDNS bufsize) to and compose request datagrams whose size does not exceed the minimum of the interface MTU, the route MTU, or the path MTU, if any are known. - If the path MTU can be reliably discovered, then such discovery SHOULD be attempted, and the result used. - For IPv6, an interface MTU other than 1500 bytes should be advertised in a Router Advertisement [RFC4861]. - If none of the MTUs are known, a default of 1500 bytes should be assumed. Further, the MTU should be reduced to account for packetization by the UDP and IP/IPv6 layers, which might add as many as 100 bytes, resulting in the RECOMMENDED 1400 Bytes. What do you think? On Sun, Jul 7, 2024 at 1:19 PM Paul Vixie <p...@redbarn.org> wrote: > Looks like the second WG mailing list fell off of this thread. See below > for history. I realize that the text I proposed to Mr. Farmer was > incoherent, so here's a second try: > > R3. UDP responders should compose response datagrams whose size does not > > exceed either the policy maximum if specified, or the requestor's offered > buffer > > size (EDNS bufsize), and will not after packetization by the UDP and > IP/IP6 > > layers (which might add as many as 100 octets) not exceed the predicted > end- > > to-end network MTU for the path to the requester. Neither the interface > MTU if > > known, or the route MTU if known, or the path MTU if known, shall be > exceeded. > > If neither the route MTU or path MTU are known, a default of 1500 should > be > > assumed. If interface, route, or path MTU can be reliably discovered, then > > such discovery SHOULD be attempted. Absent such knowledge, the lower of > > requester's offered buffer size (EDNS), or 1400, will be the maximum > datagram size for that response. The recommended 1400 value is simply 1500 > (default MTU) minus 100 (room for transport and network headers) and these > values may be revised in the future. > > If something like this can work, then something like it would have to also > be done for R5. > > -- > > P Vixie > > ---------- Forwarded Message ---------- > > Subject: [v6ops] Re: [DNSOP] Re: Fwd: New Version Notification - > draft-ietf-dnsop-avoid-fragmentation-18.txt > > Date: Saturday, July 6, 2024, 7:35:11 PM PDT > > From: Paul Vixie <paul=40redbarn....@dmarc.ietf.org> > > To: v6...@ietf.org, David Farmer <far...@umn.edu> > > On Friday, July 5, 2024 12:48:18 PM PDT David Farmer wrote: > > > Paul and Tim, > > > > > > Would this fit the bill? > > i don't think so, but it's a step in the right direction. we should not > > mention PLPMTUD since it's considered controversial in the here and now, > and > > there's no need to be provocative. > > > R3. UDP responders should compose response packets that fit in the > minimum > > > of the offered requestor's maximum UDP payload size [RFC6891], the > > > interface MTU, the network MTU value configured by the knowledge of the > > > network operators, and the RECOMMENDED maximum DNS/UDP payload size of > 1400 > > > bytes, or a different Path MTU value that is known to function without > > > encountering fragmentation, as determined by PLPMTUD [RFC 8899] or some > > > other future mechanism. (See Appendix A for more information.) > > R3. UDP responders should compose response datagrams whose size does not > > exceed either the policy maximum if specified, or the requestor's offered > buffer > > size (EDNS bufsize), and will not after packetization by the UDP and > IP/IP6 > > layers (which might add as many as 100 octets) not exceed the predicted > end- > > to-end network MTU for the path to the requester. Neither the interface > MTU if > > known, or the route MTU if known, or the path MTU if known, shall be > exceeded. > > If neither the route MTU or path MTU are known, a default of 1500 should > be > > assumed. If interface, route, or path MTU can be reliably discovered, then > > such discovery SHOULD be attempted. Absent such knowledge, either the > > requester's offered buffer size, or 1400 if lower, will be the effective > maximum > > datagram size. The 1400 value is simply 1500 (default MTU) minus 100 (room > for > > transport and network headers) and these values may be revised in the > future. > > > R5. UDP requestors should set the requestor's maximum UDP payload size > > > [RFC6891] to the RECOMMENDED maximum DNS/UDP payload size of 1400 bytes > > > unless the interface MTU or the network MTU is known to be smaller or a > > > different Path MTU value that is known to function without encountering > > > fragmentation, as determined by PLPMTUD [RFC 8899] or some other future > > > mechanism. (See Appendix A for more information.) > > i'd like to see this revised similarly to my example above, if you agree. > > -- > > P Vixie > > > _______________________________________________ > > v6ops mailing list -- v6...@ietf.org > > To unsubscribe send an email to v6ops-le...@ietf.org > > ----------------------------------------- > -- =============================================== David Farmer Email:far...@umn.edu Networking & Telecommunication Services Office of Information Technology University of Minnesota 2218 University Ave SE Phone: 612-626-0815 Minneapolis, MN 55414-3029 Cell: 612-812-9952 ===============================================
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