In DHCPv6, I would like to have access to all the information in the network packet
as in section 3 Frame Format here: https://tools.ietf.org/html/rfc2464

I've put a logging statement in:
"  Packet:", pick-first-value(binary-to-ascii(16, 8, ":", packet(0, 6)), "(none)")

This logs:
Packet:5:af:c7:f5:0:1

tcpdump of packet:
21:12:48.178994 b8:78:2e:59:3c:bd > 33:33:00:01:00:02, ethertype IPv6 (0x86dd), length 160: (flowlabel 0x401a8, hlim 1, 
next-header UDP (17) payload length: 106) fe80::8ba:eccd:e835:7ab.dhcpv6-client > ff02::1:2.dhcpv6-server: [udp sum ok] dhcp6 
renew (xid=afc7f5 (client-ID hwaddr/time type 1 time 568643687 b8782e593cbe) (option-request DNS-server DNS-search-list) 
(elapsed-time 0) (server-ID hwaddr/time type 1 time 568582025 d0d0fd09741d) (IA_NA IAID:0 T1:0 T2:0 (IA_ADDR 
2001:470:c3c7:40:ce11::4b pltime:0 vltime:0)))
     0x0000:  3333 0001 0002 b878 2e59 3cbd 86dd 6004  33.....x.Y<...`.
     0x0010:  01a8 006a 1101 fe80 0000 0000 0000 08ba ...j............
     0x0020:  eccd e835 07ab ff02 0000 0000 0000 0000 ...5............
     0x0030:  0000 0001 0002 0222 0223 006a 397c 05af  .......".#.j9|..
     0x0040:  c7f5 0001 000e 0001 0001 21e4 d067 b878 ..........!..g.x
     0x0050:  2e59 3cbe 0006 0004 0017 0018 0008 0002 .Y<.............
     0x0060:  0000 0002 000e 0001 0001 21e3 df89 d0d0 ..........!.....
     0x0070:  fd09 741d 0003 0028 0000 0000 0000 0000 ..t....(........
     0x0080:  0000 0000 0005 0018 2001 0470 c3c7 0040 ...........p...@
     0x0090:  ce11 0000 0000 004b 0000 0000 0000 0000 .......K........


As you can see, the offset of 'packet' in the IP frame is at 0x3e which doesn't
give me access to the source MAC address.  I'm trying to meld my DHCPv4
and DHCPv6 ddns updates so that I don't have to run:
update-conflict-detection    off;

I currently pull the MAC address from the DUID but that's not guaranteed to
be the real MAC address.  It might be the address of the NIC that used to be
in the machine but got replaced.  DHCPv4 receives the current MAC address.

There are several hurdles to overcome for a wider IPv6 adoption of which this
is one.  No DHCPv6 for Android is also a major pain.  I've also noticed that
Apple devices don't send zilch as far as information.  No dhcp6.fqdn ( nor
fqdn.hostname).  I suspect this is all the new 'privacy' rage but Apple devices
are merrily handing out hostname and other info for IPv4.  This may be fine
for your home network but when you administer a network of hundreds of
devices it becomes a nightmare.  With no hostname, I can't pair a IPv4
address with a IPv6 address in DNS.

I do appreciate the fine software that ISC produces.  Thanks!

Bill