This is a general overview to familiarize people interested in learning some of the lower level architecture of internetworking. To keep from covering any information that could be considered insipid, I am keeping it narrowly scoped. Any additional questions should be addressed to the response section and will be answered in discussion.
There are a couple of different types of common Ethernet frame configurations used today. They are the Ethernet_II (the 'blue book') frame, developed by Xerox, the IEEE LAN standard 802.2 and 802.3 Carrier Sense Multiple Access/Collision Detection (CSMA/CD) frame, developed by the Institute of Electrical and Electronic Engineers and Ethernet SNAP. Ethernet_II is the Internet standard. 802.2 and 802.3 are used by Novell. 802.2 is default for NetWare 3.12 and above while 802.3 is used in previous versions. Ethernet SNAP is used when AppleTalk is involved.
The Ethernet_II frame's makeup is as follows:
Bytes Element
8 Preamble
6 Destination Address (DA)
6 Source Address (SA)
2 Protocol Type
46-1500 Service Data Unit (SDU)
4 Frame Check Sequence (FCS)
5
The 802.2 (802.3 with LLC) frame's makeup is as follows:
Bytes Element
8 Preamble
6 Destination Address (DA)
6 Source Address (SA)
2 Length
1 Destination Service Access Point (DSAP)
1 Source Service Access Point (SSAP) and High Level
1 Data Link Control (HDLC)
43-1497 Service Data Unit (SDU)
4 Frame Check Sequence (FCS)
The 802.3 frame's makeup is as follows:
Bytes Element
8 Preamble
6 Destination Address (DA)
6 Source Address (SA)
2 Length
46-1500 Service Data Unit (SDU)
4 Frame Check Sequence (FCS)
The Ethernet SNAP frame's makeup is as follows:
Bytes Element
8 Preamble
6 Destination Address (DA)
6 Source Address (SA)
2 Length
1 Destination Service Access Point (DSAP)
1 Source Service Access Point (SSAP) and High Level
1 Data Link Control (HDLC)
3 Oganiztion Code
2 Ethernet Type
38-1492 Service Data Unit (SDU)
All frames start with an eight bit Preamble. After which is the Media Access Control (MAC) protocol encapsulation header consisting of the Destination Address (DA), Source Address (SA), and followed by the Type element in Ethernet_II or the Length element in 802.2, 802.3 and SNAP. The "Ethernet Type" values are managed by Xerox. Some assignments are public, others private. (chart below)
After the Length element, the 802.3 frame type can vary depending on if the incorporation of the IEEE 802.2 Logical Link Control (LLC) is being used. If used, the LLC is designed to bridge the gap in the Data Link Layer of the OSI model between the Media Access Control (MAC) sublayer and the Network Layer. When the LLC protocol is used, the MAC layer PDU (the payload data) is further encapsulated, adding two additional header fields called Service Access Points (SAPs) that identify the applications/users involved. Unlike the Destination SAP (DSAP), the Source SAP (SSAP) icludes an additional byte to define High Level Data Link Control (HDLC) mode which provides reliable data transfer using numbered control frames. If using SNAP there are 3bytes for organization code and 2 more for Ethernet Type.
At this point, the data to be transfered is pasted in. It is also important to note that if we are dealing with an 802.2 and SNAP frame, the SDU size limitations change from 46-1500 byte to 43-1497 and 38-1492 bytes (perspectivly) to accomidate for the extra encapsulation. This is to assure the packet stays below the 1518 byte 'Giant Frame' maximum and above the 64 byte 'Runt Frame' minimum. Otherwise these frame will be considered malformed and discarded.
Ethernet_II, 802.2 and 802.3 frames end by converting the Packet Data Unit (PDU) in to the Service Data Unit (SDU) element, and then creating a CRC that is stored in the Frame Check Sequence (FCS) for use in performing a quick check on data integrity at the final destination (and sometimes in route by some bridges/switches and routers).
Ethernet_II Type Element Codes:
Note Hex Definition
@ 0000-05DC IEEE802.3 Length Field (0.:1500.)
+ 0101-01FF Experimental
0200 Xerox PUP (conflicts with 802.3 Length Field
range) (see 0A00)
0201 Xerox PUP Address Translation (conflicts ...)
(see 0A01)
0400 Nixdorf (conflicts with 802.3 Length Field)
+* 0600 Xerox NS IDP
0601 XNS Address Translation (3Mb only)
+* 0800 DOD Internet Protocol (IP)
+ 0801 X.75 Internet
+ 0802 NBS Internet
+ 0803 ECMA Internet
+ 0804 CHAOSnet
+ 0805 X.25 Level 3
+* 0806 Address Resolution Protocol (ARP) (for IP and for
CHAOS)
0807 XNS Compatibility
081C Symbolics Private
+ 0888-088A Xyplex
0900 Ungermann-Bass network debugger
0A00 Xerox IEEE802.3 PUP
0A01 Xerox IEEE802.3 PUP Address Translation
0BAD Banyan Systems
0BAF Banyon VINES Echo
1000 Berkeley Trailer negotiation
1001-100F Berkeley Trailer encapsulation for IP
1234 DCA - Multicast
* 1600 VALID system protocol
1989 Artificial Horizons ("Aviator" dogfight simulator
[on Sun])
1995 Datapoint Corporation (RCL lan protocol)
3C00 3Com NBP virtual circuit datagram (like XNS SPP)
not registered
3C01 3Com NBP System control datagram not registered
3C02 3Com NBP Connect request (virtual cct) not
registered
3C03 3Com NBP Connect repsonse not registered
3C04 3Com NBP Connect complete not registered
3C05 3Com NBP Close request (virtual cct) not
registered
3C06 3Com NBP Close response not registered
3C07 3Com NBP Datagram (like XNS IDP) not registered
3C08 3Com NBP Datagram broadcast not registered
3C09 3Com NBP Claim NetBIOS name not registered
3C0A 3Com NBP Delete Netbios name not registered
3C0B 3Com NBP Remote adaptor status request not
registered
3C0C 3Com NBP Remote adaptor response not registered
3C0D 3Com NBP Reset not registered
4242 PCS Basic Block Protocol
424C Information Modes Little Big LAN diagnostic
4321 THD - Diddle
4C42 Information Modes Little Big LAN
% 5208 BBN Simnet Private
6000 DEC unassigned, experimental
6001 DEC Maintenance Operation Protocol (MOP)
Dump/Load Assistance
6002 DEC Maintenance Operation Protocol (MOP) Remote
Console
6003 DECNET Phase IV, DNA Routing
6004 DEC Local Area Transport (LAT)
6005 DEC diagnostic protocol (at interface
initialization?)
6006 DEC customer protocol
6007 DEC Local Area VAX Cluster (LAVC), System
Communication Architecture (SCA)
6008 DEC AMBER
6009 DEC MUMPS
+ 6010-6014 3Com Corporation
7000 Ungermann-Bass download
7001 Ungermann-Bass NIUs
7002 Ungermann-Bass diagnostic/loopback
7003 Ungermann-Bass ??? (NMC to/from UB Bridge)
7005 Ungermann-Bass Bridge Spanning Tree
7007 OS/9 Microware
7009 OS/9 Net?
+ 7020-7029 LRT (England) (now Sintrom)
7030 Racal-Interlan
7031 Prime NTS (Network Terminal Service)
7034 Cabletron
8003 Cronus VLN
8004 Cronus Direct
8005 HP Probe protocol
+ 8006 Nestar
+ 8008 AT&T/Stanford Univ. Local use
8010 Excelan
+ 8013 Silicon Graphics diagnostic
+ 8014 Silicon Graphics network games
+ 8015 Silicon Graphics reserved
+ 8016 Silicon Graphics XNS NameServer, bounce server
+ 8019 Apollo DOMAIN
+ 802E Tymshare
+ 802F Tigan, Inc.
+ 8035 Reverse Address Resolution Protocol (RARP)
+ 8036 Aeonic Systems
8037 IPX (Novell Netware?)
8038 DEC LanBridge Management
8039 DEC DSM/DDP
803A DEC Argonaut Console
803B DEC VAXELN
803C DEC DNS Naming Service
803D DEC Ethernet CSMA/CD Encryption Protocol
803E DEC Distributed Time Service
803F DEC LAN Traffic Monitor Protocol
8040 DEC PATHWORKS DECnet NETBIOS Emulation
8041 DEC Local Area System Transport
8042 DEC unassigned
+ 8044 Planning Research Corp.
+ 8046 AT&T
+ 8047 AT&T
8048 DEC Availability Manager for Distributed Systems
DECamds (but someone at DEC says not)
+ 8049 ExperData
+ 805B VMTP (Versatile Message Transaction Protocol, RFC-
1045) (Stanford) [experimental]
+ 805C Stanford V Kernel, version 6.0
+ 805D Evans & Sutherland
+ 8060 Little Machines
+ 8062 Counterpoint Computers
+ 8065 University of Mass. at Amherst
+ 8066 University of Mass. at Amherst
+ 8067 Veeco Integrated Automation
+ 8068 General Dynamics
+ 8069 AT&T
+ 806A Autophon
+ 806C ComDesign
+ 806D Compugraphic Corporation
+ 806E-8077 Landmark Graphics Corporation
+ 807A Matra
+ 807B Dansk Data Elektronik
+ 807C Merit Internodal (or Univ of Michigan?)
+ 807D-807F Vitalink Communications
+ 8080 Vitalink TransLAN III Management
+ 8081-8083 Counterpoint Computers
8088-808A Xyplex
+ 809B EtherTalk (AppleTalk over Ethernet)
+ 809C-809E Datability
+ 809F Spider Systems Ltd.
+ 80A3 Nixdorf Computers
+ 80A4-80B3 Siemens Gammasonics Inc.
+ 80C0-80C3 DCA (Digital Comm. Assoc.) Data Exchange
Cluster
+ 80C6 Pacer Software
+ 80C7 Applitek Corporation
+ 80C8-80CC Intergraph Corporation
+ 80CD-80CE Harris Corporation
+ 80CF-80D2 Taylor Instrument
+ 80D3-80D4 Rosemount Corporation
80D5 IBM SNA Services over Ethernet
+ 80DD Varian Associates
+ 80DE-80DF TRFS (Integrated Solutions Transparent
Remote File System)
+ 80E0-80E3 Allen-Bradley
+ 80E4-80F0 Datability
+ 80F2 Retix
+ 80F3 AppleTalk Address Resolution Protocol (AARP)
+ 80F4-80F5 Kinetics
+ 80F7 Apollo Computer
+ 80FF-8101 Wellfleet Communications
+ 8102 Wellfleet; BOFL (Breath OF Life) pkts [every 5-10
secs.]
+ 8103 Wellfleet Communications
8107-8109 Symbolics Private
812B Talaris
+ 8130 Waterloo Microsystems Inc.
+ 8131 VG Laboratory Systems
+ 8137 Novell (old) NetWare IPX (ECONFIG E option)
+ 8138 Novell, Inc.
+ 8139-813D KTI
813F M/MUMPS data sharing
8145 Vrije Universiteit (NL) Amoeba 4 RPC (obsolete)
8146 Vrije Universiteit (NL) FLIP (Fast Local
Internet Protocol)
8147 Vrije Universiteit (NL) [reserved]
814C SNMP over Ethernet (see RFC1089)
814F Technically Elite Concepts Network Professor
8191 PowerLAN NetBIOS/NetBEUI (PC)
817D XTP
81D6 Artisoft Lantastic
81D7 Artisoft Lantastic
8203-8205 QNX Software Systems Ltd.
8390 Accton Technologies (unregistered)
852B Talaris multicast
8582 Kalpana
86DD IP version 6
8739 Control Technology Inc. RDP Without IP
873A Control Technology Inc. Mcast Industrial Ctrl
Proto.
873B Control Technology Inc. Proprietary
873C Control Technology Inc. Proprietary
8820 Hitachi Cable (Optoelectronic Systems Laboratory)
8856 Axis Communications AB proprietary
bootstrap/config
8888 HP LanProbe test?
+ 9000 Loopback (Configuration Test Protocol)
9001 3Com (Formerly Bridge Communications), XNS
Systems Management
9002 3Com (Formerly Bridge Communications), TCP/IP
Systems Management
9003 3Com (Formerly Bridge Communications), loopback
detection
AAAA DECNET? Used by VAX 6220 DEBNI
FAF5 Sonix Arpeggio
% FF00 BBN VITAL-LanBridge cache wakeups
Notes:
* These protocols use Ethernet broadcast, where multicast would be preferable.
% Possible Private Protocols, i.e. not registered
+ These are publicly assigned numbers. Only vendors are listed by Xerox, not protocols.
@ Anything less than 600H, the packet is assumed to be an 802.3 packet; if it is greater than 600H, the packet is flagged as an Ethernet packet.
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