Enterasys Networks 700 - Manual (Page 161)

Configuring FDDI Frame Translation Settings 5-17
FDDI Management
This is the default frame type for Novell NetWare software version 3.12 and
beyond; it is also used for OSI packets on IEEE 802.x LAN networks.
Ethernet 802.3 (Ethernet Raw)
The Ethernet 802.3 frame format has an 802.3 MAC layer header (as do Ethernet
802.2 frames); however, it does not contain an 802.2 LLC header. Instead, Novell
IPX is fixed within the packet as the network layer protocol. This frame type – also
known as Raw 802.3 – is the default frame type for Novell NetWare
software
before version 3.11. Since these frames do not carry the 802.2 header, they do not
conform to the IEEE 802.3 specification. If you are using the Ethernet 802.3 Raw
frame format, you should consider upgrading your Novell NetWare software to
ensure interoperability with other communications protocols (unless your current
network is not likely to be upgraded, and has no interoperability problems).
Note that IPX packets with checksums which provide data integrity (a feature of
newer Novell NetWare releases) cannot be transmitted on Ethernet 802.3
networks. Note also that a single Ethernet can carry both Ethernet 802.3 and
Ethernet 802.2 traffic simultaneously. The Novell server software will treat the
two frame types as two logical networks (and function as an IPX router between
the two networks).
Ethernet SNAP
To allow for proprietary protocols, such as IBM’s SNA protocol, the Ethernet
SNAP frame was created. This frame format extended the Ethernet 802.2 packet
by improving the frame’s byte alignment, and by allowing further protocol
identification than the one byte LSAP protocol identifier of Ethernet 802.2 frames
(which is reserved for standard protocols). Ethernet SNAP packets have an LSAP
protocol ID of hex AA, indicating that they contain a SNAP (Subnetwork Access
Protocol) packet. A SNAP packet, encapsulated within the Ethernet 802.2 packet,
has a five byte SNAP header which is simply a five byte protocol identifier. The
first three bytes of the header indicate the Organizationally Unique Identifier
(OUI) – or the authority assigning the protocol ID – and the last two bytes indicate
the protocol according to that authority. Note that for most protocols, the OUI is
0-0-0, and the type identifier is the standard Ethernet protocol ID. Although most
Ethernet transport protocols use the Ethernet II frame format, the AppleTalk II
protocol uses Ethernet SNAP (AppleTalk has its own unique OUI).
FDDI Frames
There are two legal FDDI data frame types:
FDDI 802.2
The FDDI 802.2 frame type has two headers: the FDDI header (which includes the
Frame Control field that indicates the class of frame, length of the address field,
and the type of FDDI frame), and the 802.2 header.