Hi Joe, annotations below again: Thank you - Fred
From: to...@strayalpha.com <to...@strayalpha.com> Sent: Monday, September 30, 2024 8:57 AM To: Templin (US), Fred L <fred.l.temp...@boeing.com> Cc: Brian Carpenter <brian.e.carpen...@gmail.com>; Gorry (erg) <go...@erg.abdn.ac.uk>; Tim Chown <tim.ch...@jisc.ac.uk>; Internet Area <Int-area@ietf.org>; IPv6 List <i...@ietf.org>; tsvwg IETF list <ts...@ietf.org> Subject: Re: UDP options [was IP Parcels and Advanced Jumbos (AJs)] On Sep 30, 2024, at 8:41 AM, Templin (US), Fred L <Fred.L.Templin=40boeing....@dmarc.ietf.org<mailto:Fred.L.Templin=40boeing....@dmarc.ietf.org>> wrote: >> For parcels/AJs >= 64K, the overall length appears in the Parcel Payload >> Length of the HBH option and >> the UDP length is set to 0. The IP parcels draft specifies that UDP Length = >> 0 means that there will be >> a trailing 2-octet UDP Option Length field beyond the end of what would be >> considered the UDP options. >> The trailing field is not part of the UDP options, but is used to determine >> the starting offset and length >> of the UDP options. Again, this is only for parcels/AJs >= 64K. I’m not sure I understand; it seems like somebody needs to adjust that PPL HBH option. Either: PPL HBH gives total packet length then UDP options has to know to adjust that by -2 UDP options currently takes what it gets from the IP layer length; PPL HBH would need to know to subtract that by 2 for UDP, maybe something else for TCP or other transports. >> The IP layer of the source inserts a Parcel Payload Hop-by-Hop option as the >> final step prior to >> transmission of the parcel/AJ. The HBH option includes a Parcel Payload >> Length field that encodes >> the length of the IP header for IPv4 or the extension headers for IPv6, plus >> the length of the UDP >> packet that follows, plus the length of the UDP options, plus the length of >> the UDP Option Length >> field (i.e., either 0 octets if UDP length is non-zero or 2 octets if UDP >> length is 0). The IP layer of >> the destination then parses the HBH option as its first step upon reception >> of the parcel/AJ. >> The destination can then set up for processing UDP options based on whether >> a UDP Options >> Length field is included or whether the standard UDP length field is >> non-zero. >> >> The key thing is that the parcel/AJ HBH option is added as the final step >> before transmission >> and parsed as the first step upon reception. The source and destination can >> therefore work >> with octets that appear beyond what would be considered the end of the UDP >> surplus area. ?? Joe
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