[DNSOP] udp options draft

[Paul Vixie <[e-mail]>]

as most dns technologists are aware, ip and tcp have options, and udp does 
not. there is a draft:

https://datatracker.ietf.org/doc/draft-ietf-tsvwg-udp-options/

which has been ongoing since 2015, which proposes to add options to udp:

Internet-Draft        Transport Options for UDP         September 2019

                             IP transport payload
                <------------------------------------------------->
      +--------+---------+----------------------+------------------+
      | IP Hdr | UDP Hdr |     UDP user data    |   surplus area   |
      +--------+---------+----------------------+------------------+
                <------------------------------>
                           UDP Length

               Figure 3 IP transport payload vs. UDP Length

this relies on the unaccounted octets which follow the udp header and data, 
inside the ip length but outside the udp length. this is moderately 
controversial since it's a deliberate layering violation, but it may be more 
workable than creating a new "udp2" ip datagram type, due to middleboxes.

the options proposed are:

Internet-Draft        Transport Options for UDP         September 2019

             Kind    Length    Meaning
             ----------------------------------------------
             0*      -         End of Options List (EOL)
             1*      -         No operation (NOP)
             2*      3         Option checksum (OCS)
             3*      6         Alternate checksum (ACS)
             4*      4         Lite (LITE)
             5*      4         Maximum segment size (MSS)
             6*      8/10      Fragmentation (FRAG)
             7       10        Timestamps (TIME)
             8       (varies)  Authentication and Encryption (AE)
             9       6         Request (REQ)
             10      6         Response (RES)
             11-126  (varies)  UNASSIGNED (assignable by IANA)
             127-253           RESERVED
             254     N(>=4)    RFC 3692-style experiments (EXP)
             255               Reserved

since dns has been the greatest single user of wide area udp, i suggest that 
those in dnsop who have an interest in this topic, please review this draft. 
something of this form will likely be created, in order to support quic, a new 
udp based transport protocol which is expected to be used by http/3.

-- 
Paul