Ethernet

A full description of Ethernet is beyond the scope of this document; some basic information on Ethernet and its use with NetBIOS is given below.

Ethernet is widely used today and well documented. Four types of Ethernet frames have been in common use. For convenience the notation used by Novell is used to describe the four Ethernet frame types:

Ethernet_802.3

Known as Ethernet 802.3 raw, this frame type is used in NetWare networks and was the default type in NetWare v2.x and v3.x

Ethernet_II

Known as Ethernet DIX (Developed by Digital Intel Xerox)

Ethernet_802.2

IEEE Ethernet

Ethernet_SNAP

SNAP (Sub-Network Access Protocol) derived from the Ethernet 802.2 structure

Ethernet_802.3

Known as Ethernet 802.3 raw, this frame type is used in NetWare networks and was the default type in NetWare v2.x and v3.x Because of the nature of these frames they are unlikely to carry NBF frames, unless encapsulated in IPX.

Table 2. Ethernet_802.3 Frame Structure

Preamble 7 octets
Start frame deliminator 1 octet
Destination Address 6 octets
Source Address 6 octets
Length 2 octets
Data 46-1500 octets
Frame Check sequence 4 octets

Ethernet_802.2

NBF frames are found in Ethernet_802.2 frames more than in other Ethernet frames when NBF is implemented "on the wire" rather than encapsulated.

Ethernet_802.2 frames are also used with IPX/SPX and FTAM (File Transfer Access and Management) protocol.

Table 3. Ethernet_802.2 Frame Structure

Ethernet frame 802.2 Frame detail NBF frame
Preamble 7 octets    
Start frame deliminator 1 octet
Destination Address 6 octets
Source Address 6 octets
Length 2 octets
IEEE 802.2 Logical Link Control DSAP 2 octets
SSAP 2 octets
Control 1 or 2 octets
Data 46-1500 octets NetBIOS header
Optional data
Frame Check sequence 4 octets    

Ethernet_SNAP

Ethernet_SNAP frames are used by IPX/SPX, TCP/IP and AppleTalk Phase II.

Table 4. Ethernet_SNAP Frame Structure

Preamble 7 octets
Start frame deliminator 1 octet
Destination Address 6 octets
Source Address 6 octets
Length 2 octets
DSAP 2 octets value AA
SSAP 2 octets value AA
Control 1 octets
Organizational code 3 octets
Ethernet Type 2 octets
Data 46-1500 octets
Frame Check sequence 4 octets

Ethernet_II

Ethernet_II frames are used with IPX/SPX TCP/IP AppleTalk Phase I

Following the source address, is an Ethernet frame type. Information on Ethernet frame types can be found at: http://www.iana.org/assignments/ethernet-numbers and at: http://www.cavebear.com/CaveBear/Ethernet/type.html

For SNA (Systems Network Architecture) communications the value registered for the type is 0x80D5. This value of 0x80D5 is also used for other systems using the IEEE 802.2 API including NetBIOS

Table 5. Ethernet_II Frame Structure

Preamble 8 octets
Destination Address 6 octets
Source Address 6 octets
Ethernet Type 2 octets
Data 46-1500 octets
Frame Check sequence 4 octets

Further information

Many manuals and documents describe Ethernet in detail including Novell's Guide to NetWare LAN Analysis, see Bibliography