// interactive wire-format field guide
Packets are just bits.
Read them precisely.
Bit diagrams with exact offsets, reserved bits, valid ranges and RFC citations for every field. Build a header from its fields, or paste raw hex to inspect and validate it in the browser. No capture file required.
// the tcp/ip model
Where every protocol lives.
click a layer to filter · click a protocol to open
// protocol index
Pick a header. See every bit.
13 protocols · 17 pages
field sheets by layer
IPv4 & options
The 20-byte workhorse, fragmentation flags, DSCP/ECN, checksum, and the TLV option space everyone forgets.
ICMP errors & echo
Type/code semantics, checksum coverage, rest-of-header variants, quoted original datagrams and RFC 4884 extensions.
IPv6 & extension chain
Fixed 40-byte header, 128-bit addresses, traffic class and flow label, extension headers, jumbograms and RFC 5952 text.
TCP flags & TLVs
Eight control bits, the option kind registry, MSS, window scale, SACK and timestamps — plus scan recipes.
UDP datagrams
Ports, length, checksum, IPv4 and IPv6 pseudo-headers, service lookup and a decoded port-to-port flow.
QUIC frames
Long and short headers, the 2-bit varint prefix, STREAM/ACK/CRYPTO frames and a frame-level codec.
BGP path attributes
Optional/transitive/partial flags, extended lengths, AS_PATH segments, communities and MP_REACH_NLRI.
DNS records & flags
Header flags, questions, resource records, name-compression pointers, EDNS(0) and a query/response codec.
DHCP leases & options
BOOTP header, broadcast flag, message types, lease timers, option overload, relay agent information and a message codec.
HTTP requests & frames
Request and status lines, header fields, Content-Length and chunked framing, HTTP/2 frames and HPACK header compression.
TLS 1.3 records & hello
Record layer, ClientHello and ServerHello, extensions, the HKDF key schedule, alerts and the encrypted boundary.
Ethernet II frames
Destination and source MACs, EtherType, 802.1Q VLAN tags, padding and the CRC-32 frame check sequence.
ARP
IPv4-to-MAC resolution, request/reply opcodes, ARP probes, gratuitous ARP and Ethernet padding.
Packet dissector
One frame, every layer: Ethernet, VLAN, IP, TCP/UDP/ICMP, DNS, HTTP, TLS and opaque payloads with offset-linked hex.
// field index
Find a field without opening five PDFs.
try “SACK”, “fragment”, “varint”, “0x94”