Ethernet uses the type field to determine the packet protocol. 802.3/802.2
use the DSAP and SSAP fields.
Because there are only 256 possible SAP values, they are fairly hard to get.
The special SAP number of AA was assigned to indicate that there are
further headers after the 802.2 header that must be parsed to determine the
network-level protocol. This is the SNAP header that uses the same type
field used by V2 Ethernet.
IP on an Ethernet can be indicated by Ethernet V2 type 0x0800, 802.2 SAP
code 0x06; or a SAP code of 0xAA followed by a SNAP type code of 0x0800.
AppleTalk can be indicated by either Ethernet V2 type 0x809B (Phase I), or
a SAP code of 0xAA followed by a SNAP type code of 0x809B (Phase II).
AppleTalk is currently never sent as an 802.3/802.2 packet with a unique
Novell can be found as either Ethernet type 0x8137, or a raw 802.3 packet.
It is not sent as an 802.3/802.2 packet with a unique SAP code.
There are only a few SAP values that you are likely to run across. They are:
04 - IBM SNA
06 - IP
80 - 3Com
AA - SNAP
BC - Banyan
E0 - Novell (TR)
F4 - Lan Manager FE - CLNS
FDDI Encapsulation Methods
On FDDI you have only three encapsulation formats:
FDDI with LLC
FDDI with LLC and SNAP
Cisco: ipx encapsulation fddi-raw (IOS 11.1.x and up)
Novell: FDDI_raw (used only from third-party vendors, not from Novell)