[Int-area] Re: UDP options [was IP Parcels and Advanced Ju mbos (AJs)]

Hi Joe, annotations below again:

Thank you - Fred

From: [email protected] <[email protected]>
Sent: Monday, September 30, 2024 8:57 AM
To: Templin (US), Fred L <[email protected]>
Cc: Brian Carpenter <[email protected]>; Gorry (erg) <[email protected]>; Tim Chown <[email protected]>; Internet Area <[email protected]>; IPv6 List <[email protected]>; tsvwg IETF list <[email protected]>
Subject: Re: UDP options [was IP Parcels and Advanced Jumbos (AJs)]

On Sep 30, 2024, at 8:41 AM, Templin (US), Fred L <[email protected]<mailto:[email protected]>> 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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