Does this resolve the type mismatch? Do you have any other concerns? R3. UDP responders should compose response datagrams whose size does not exceed the requestor's offered buffer size (EDNS bufsize) or, after packetization by the UDP and IP/IPv6 layers, does not exceed the interface MTU, the route MTU, or the path MTU, if they 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. Considering packetization, which might add as many as 100 bytes, the RECOMMENDED buffer size is 1400 bytes. R5. UDP requestors should set the requestor's offered buffer size (EDNS bufsize) to and compose request datagrams whose size, after packetization by the UDP and IP/IPv6 layers, does not exceed the interface MTU, the route MTU, or the path MTU, if they 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. Considering packetization, which might add as many as 100 bytes, the RECOMMENDED buffer size is 1400 bytes. On Sun, Jul 7, 2024 at 8:41 PM Paul Vixie <p...@redbarn.org> wrote: > see inline. > > On Sunday, July 7, 2024 3:55:36 PM PDT David Farmer wrote: > > > Paul, > > > > > > I think this might be a little easier for people to parse, and I think it > > > covers everything in yours; > > that attempt is visible, but there's a fine point it loses. > > > 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. > > a datagram == a udp payload. it is subject to limitation by remote bufsize > or local policy. the estimated or discovered MTU has to be 100 octets > larger than that. so the above paragraph has a type error. so while this > formulation is clearer than mine, it's also incorrect, and as you can see > in my "second try" draft, i think the difference is important. > > re: > > > > > > - 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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