Add NTP and DHCP L7 dissectors

NTP decodes the fixed header's version/mode/stratum - the timestamp
fields need NTP era/fraction fixed-point math to render meaningfully
and add nothing a one-line summary needs, so they're left alone.

DHCP decodes RFC 2131's BOOTP fixed header + magic cookie, then walks
the TLV options bounds-safely for option 53 (message type), plus
yiaddr when the server has assigned one. It's the first dissector
needing two well-known ports (67 server, 68 client) rather than one;
registering at just 67 still matches both directions since
l7_summarize() already falls back from dst_port to src_port.

Verified live: NTP against a real pool.ntp.org query on wlp1s0 (a
genuine stratum-2 reply came back). DHCP over loopback with a
synthetic-but-wire-format-real DISCOVER/OFFER exchange rather than a
real lease renewal, to avoid disrupting this machine's actual network
state - caught a test-setup mistake in the process (both packets
sent from the same ephemeral port instead of the OFFER actually
originating from port 67), not a dissector bug.

1 files changed, 31 insertions, 0 deletions

diff --git a/PLAN.md b/PLAN.md
index 5c0f2f1..c384e20 100644
--- a/PLAN.md
+++ b/PLAN.md
@@ -406,3 +406,34 @@ None currently open.
   split-segment HTTP scenario used to verify -a on the CLI and GUI:
   both "checksums: IP=ok TCP=..." and "[reassembled request: ... Host:
   ... (72 bytes so far)]" appeared correctly inline in the packet list.
+- NTP (packeteer/l7/ntp.hpp) and DHCP (packeteer/l7/dhcp.hpp)
+  dissectors. NTP decodes only the first two header bytes (version,
+  mode, stratum) - the timestamp fields need NTP era/fraction
+  fixed-point math to render meaningfully and add nothing a one-line
+  summary needs, so they're left alone. DHCP decodes RFC 2131's fixed
+  236-byte BOOTP header + 4-byte magic cookie, then walks the
+  variable-length TLV options bounds-safely to find option 53 (message
+  type) - the one field that actually says DISCOVER/OFFER/REQUEST/ACK/
+  etc; other options are skipped over, not decoded. yiaddr (the address
+  being offered/assigned) is shown when non-zero since it's genuinely
+  new information, not a repeat of the IPv4 line's src/dst above it --
+  formatted with a small local snprintf helper inside dhcp.hpp rather
+  than reusing summarize.hpp's ipv4_to_string, since summarize.hpp
+  already depends on this header and the reverse include would be
+  circular (same reasoning as arp_summary living in summarize.hpp
+  instead of arp.hpp, just resolved in the other direction here).
+  DHCP is the first dissector needing two well-known ports (67 server,
+  68 client) rather than one; registering at just 67 still matches
+  both directions because l7_summarize() already falls back from
+  dst_port to src_port. Verified live: NTP against a real query to
+  pool.ntp.org on wlp1s0 ("NTP v4 client stratum=0" request, "NTP v4
+  server stratum=2" reply from an actual stratum-2 timeserver at
+  196.10.55.57). DHCP verified over loopback with a synthetic-but-
+  wire-format-real DISCOVER/OFFER exchange (not a real DHCP renewal,
+  to avoid disrupting this machine's actual network state) - caught a
+  test-setup mistake in the process, not a dissector bug: the first
+  attempt sent both packets from the same arbitrary ephemeral port, so
+  the OFFER's source port never matched DHCP's server port and nothing
+  decoded; fixed by actually binding the "server" send to port 67 (as
+  real DHCP servers do), which then correctly decoded "DHCP OFFER
+  yiaddr=192.168.1.50" on top of "DHCP DISCOVER" for the request.