LPDU

The LLC protocol data unit — an LLC header, a SNAP extension, and the payload they describe.

Reading a capture

The layer that answers "what is inside this frame?". Ethernet answers it in two octets; 802.11 needs eight, because 802.2 was designed before EtherType won and SNAP exists to carry an EtherType through it anyway.

Subfields

• DSAP — Destination service access point. Always 0xAA when SNAP follows.
• SSAP — Source service access point. Always 0xAA when SNAP follows.
• Control — Always 0x03, meaning unnumbered information — no sequencing, no acknowledgement at this layer.
• OUI — Organizationally unique identifier. All zeroes means the next field is an EtherType.
• EtherType — What protocol the payload is.

Where it sits

LPDU

Authored in LLC with SNAP header . Drawn in 11 frames.

• TCP over IPv4, in a protected QoS Data frame, aggregated
• Four-way handshake message 1
• Four-way handshake message 2
• Four-way handshake message 3
• Four-way handshake message 4
• ARP request in a QoS Data frame
• ICMP echo over IPv4, in a QoS Data frame
• UDP over IPv6, in a QoS Data frame
• TCP over IPv4, in a protected QoS Data frame
• TCP over IPv4, in an open QoS Data frame
• UDP over IPv4, in a QoS Data frame

Accuracy

Clause

IEEE 802.2 §3.2; RFC 1042

Verified

Not verified against the standard. Treat this as a claim, not a fact.