Lets look at different Ethernet frames first: (Cisco Link)
- Ethernet II or DIX Frames:
- Most popular
- Ether Type is used for indicating upper layer protocol.
- Exists prior to standardization work started by IEEE.
- IEEE 802.3 Skeleton:
- Treats ether type as length instead of protocol
- Just a skeleton (as there is no field to indicate upper layer protocol)
- Used to hold IEEE standardized Ethernet frames (discussed next).
- IEEE 802.3 with 802.2 LLC
- Define 3 bytes LLC header (DSAP, SSAP, Control) taken from HDLC.
- DSAP & SSAP refers to Destination SAP & Source SAP.
- DSAP and SSAP are just one byte field and hence not capable to hold upper protocol type (need 2 bytes for that). IEEE introduced SNAP header to remove this limitation.
- IEEE 802.3 with 802.2 LLC/SNAP
- DSAP & SSAP of LLC header are fixed to 0xAA and control field is fixed to 0x03.
- SNAP header is of 5 bytes (3 bytes for OUI & 2 bytes for specifying protocol)
- In wireless frame, OUI is 00-00-00.
Note: Ether Type > 1536 (0x600) indicates the Ethernet II frame.