This material is extracted from RFC 1340 "Assigned Numbers". Data Notations The convention in the documentation of Internet Protocols is to express numbers in decimal and to picture data in "big-endian" order [COHEN]. That is, fields are described left to right, with the most significant octet on the left and the least significant octet on the right. The order of transmission of the header and data described in this document is resolved to the octet level. Whenever a diagram shows a group of octets, the order of transmission of those octets is the normal order in which they are read in English. For example, in the following diagram the octets are transmitted in the order they are numbered. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1 | 2 | 3 | 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 5 | 6 | 7 | 8 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 9 | 10 | 11 | 12 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Transmission Order of Bytes Whenever an octet represents a numeric quantity the left most bit in the diagram is the high order or most significant bit. That is, the bit labeled 0 is the most significant bit. For example, the following diagram represents the value 170 (decimal). 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |1 0 1 0 1 0 1 0| +-+-+-+-+-+-+-+-+ Significance of Bits Similarly, whenever a multi-octet field represents a numeric quantity the left most bit of the whole field is the most significant bit. When a multi-octet quantity is transmitted the most significant octet is transmitted first. Special Addresses There are five classes of IP addresses: Class A through Class E. Of these, Classes A, B, and C are used for unicast addresses, Class D is used for multicast addresses, and Class E addresses are reserved for future use. With the advent of classless addressing [CIDR1, CIDR2], the network-number part of an address may be of any length, and the whole notion of address classes becomes less important. There are certain special cases for IP addresses. These special cases can be concisely summarized using the earlier notation for an IP address: IP-address ::= { , } or IP-address ::= { , , } if we also use the notation "-1" to mean the field contains all 1 bits. Some common special cases are as follows: (a) {0, 0} This host on this network. Can only be used as a source address (see note later). (b) {0, } Specified host on this network. Can only be used as a source address. (c) { -1, -1} Limited broadcast. Can only be used as a destination address, and a datagram with this address must never be forwarded outside the (sub-)net of the source. (d) {, -1} Directed broadcast to specified network. Can only be used as a destination address. (e) {, , -1} Directed broadcast to specified subnet. Can only be used as a destination address. (f) {, -1, -1} Directed broadcast to all subnets of specified subnetted network. Can only be used as a destination address. (g) {127, } Internal host loopback address. Should never appear outside a host. IANA ETHERNET ADDRESS BLOCK The IANA owns an Ethernet address block which may be used for multicast address asignments or other special purposes. The address block in IEEE binary is: 0000 0000 0000 0000 0111 1010 In the normal Internet dotted decimal notation this is 0.0.94 since the bytes are transmitted higher order first and bits within bytes are transmitted lower order first (see "Data Notation" in the Introduction). IEEE CSMA/CD and Token Bus bit transmission order: 00 00 5E IEEE Token Ring bit transmission order: 00 00 7A Appearance on the wire (bits transmitted from left to right): 0 23 47 | | | 1000 0000 0000 0000 0111 1010 xxxx xxx0 xxxx xxxx xxxx xxxx | | Multicast Bit 0 = Internet Multicast 1 = Assigned by IANA for other uses Appearance in memory (bits transmitted right-to-left within octets, octets transmitted left-to-right): 0 23 47 | | | 0000 0001 0000 0000 0101 1110 0xxx xxxx xxxx xxxx xxxx xxxx | | Multicast Bit 0 = Internet Multicast 1 = Assigned by IANA for other uses The latter representation corresponds to the Internet standard bit-order, and is the format that most programmers have to deal with. Using this representation, the range of Internet Multicast addresses is: 01-00-5E-00-00-00 to 01-00-5E-7F-FF-FF in hex, or 1.0.94.0.0.0 to 1.0.94.127.255.255 in dotted decimal ETHERNET VENDOR ADDRESS COMPONENTS Ethernet hardware addresses are 48 bits, expressed as 12 hexadecimal digits (0-9, plus A-F, capitalized). These 12 hex digits consist of the first/left 6 digits (which should match the vendor of the Ethernet interface within the station) and the last/right 6 digits which specify the interface serial number for that interface vendor. Ethernet addresses might be written unhyphenated (e.g., 123456789ABC), or with one hyphen (e.g., 123456-789ABC), but should be written hyphenated by octets (e.g., 12-34-56-78-9A-BC). These addresses are physical station addresses, not multicast nor broadcast, so the second hex digit (reading from the left) will be even, not odd. At present, it is not clear how the IEEE assigns Ethernet block addresses. Whether in blocks of 2**24 or 2**25, and whether multicasts are assigned with that block or separately. A portion of the vendor block address is reportedly assigned serially, with the other portion intentionally assigned randomly. If there is a global algorithm for which addresses are designated to be physical (in a chipset) versus logical (assigned in software), or globally-assigned versus locally-assigned addresses, some of the known addresses do not follow the scheme (e.g., AA0003; 02xxxx). 00000C Cisco 00000E Fujitsu 00000F NeXT 000010 Sytek 00001D Cabletron 000020 DIAB (Data Intdustrier AB) 000022 Visual Technology 00002A TRW 000032 GPT Limited (reassigned from GEC Computers Ltd) 00005A S & Koch 00005E IANA 000065 Network General 00006B MIPS 000077 MIPS 00007A Ardent 000089 Cayman Systems Gatorbox 000093 Proteon 00009F Ameristar Technology 0000A2 Wellfleet 0000A3 Network Application Technology 0000A6 Network General (internal assignment, not for products) 0000A7 NCD X-terminals 0000A9 Network Systems 0000AA Xerox Xerox machines 0000B3 CIMLinc 0000B7 Dove Fastnet 0000BC Allen-Bradley 0000C0 Western Digital 0000C5 Farallon phone net card 0000C6 HP Intelligent Networks Operation (formerly Eon Systems) 0000C8 Altos 0000C9 Emulex Terminal Servers 0000D7 Dartmouth College (NED Router) 0000D8 3Com? Novell? PS/2 0000DD Gould 0000DE Unigraph 0000E2 Acer Counterpoint 0000EF Alantec 0000FD High Level Hardvare (Orion, UK) 000102 BBN BBN internal usage (not registered) 0020AF 3COM ??? 001700 Kabel 008064 Wyse Technology / Link Technologies 00802B IMAC ??? 00802D Xylogics, Inc. Annex terminal servers 00808C Frontier Software Development 0080C2 IEEE 802.1 Committee 0080D3 Shiva 00AA00 Intel 00DD00 Ungermann-Bass 00DD01 Ungermann-Bass 020701 Racal InterLan 020406 BBN BBN internal usage (not registered) 026086 Satelcom MegaPac (UK) 02608C 3Com IBM PC; Imagen; Valid; Cisco 02CF1F CMC Masscomp; Silicon Graphics; Prime EXL 080002 3Com (Formerly Bridge) 080003 ACC (Advanced Computer Communications) 080005 Symbolics Symbolics LISP machines 080008 BBN 080009 Hewlett-Packard 08000A Nestar Systems 08000B Unisys 080011 Tektronix, Inc. 080014 Excelan BBN Butterfly, Masscomp, Silicon Graphics 080017 NSC 08001A Data General 08001B Data General 08001E Apollo 080020 Sun Sun machines 080022 NBI 080025 CDC 080026 Norsk Data (Nord) 080027 PCS Computer Systems GmbH 080028 TI Explorer 08002B DEC 08002E Metaphor 08002F Prime Computer Prime 50-Series LHC300 080036 Intergraph CAE stations 080037 Fujitsu-Xerox 080038 Bull 080039 Spider Systems 080041 DCA Digital Comm. Assoc. 080045 ???? (maybe Xylogics, but they claim not to know this number) 080046 Sony 080047 Sequent 080049 Univation 08004C Encore 08004E BICC 080056 Stanford University 080058 ??? DECsystem-20 08005A IBM 080067 Comdesign 080068 Ridge 080069 Silicon Graphics 08006E Concurrent Masscomp 080075 DDE (Danish Data Elektronik A/S) 08007C Vitalink TransLAN III 080080 XIOS 080086 Imagen/QMS 080087 Xyplex terminal servers 080089 Kinetics AppleTalk-Ethernet interface 08008B Pyramid 08008D XyVision XyVision machines 080090 Retix Inc Bridges 484453 HDS ??? 800010 AT&T AA0000 DEC obsolete AA0001 DEC obsolete AA0002 DEC obsolete AA0003 DEC Global physical address for some DEC machines AA0004 DEC Local logical address for systems running DECNET ETHERNET MULTICAST ADDRESSES An Ethernet multicast address consists of the multicast bit, the 23-bit vendor component, and the 24-bit group identifier assigned by the vendor. For example, DEC is assigned the vendor component 08-00-2B, so multicast addresses assigned by DEC have the first 24-bits 09-00-2B (since the multicast bit is the low-order bit of the first byte, which is "the first bit on the wire"). Ethernet Type Address Field Usage Multicast Addresses: 01-00-5E-00-00-00- 0800 Internet Multicast [RFC1112] 01-00-5E-7F-FF-FF 01-00-5E-80-00-00- ???? Internet reserved by IANA 01-00-5E-FF-FF-FF 01-80-C2-00-00-00 -802- Spanning tree (for bridges) 09-00-02-04-00-01? 8080? Vitalink printer 09-00-02-04-00-02? 8080? Vitalink management 09-00-09-00-00-01 8005 HP Probe 09-00-09-00-00-01 -802- HP Probe 09-00-09-00-00-04 8005? HP DTC 09-00-1E-00-00-00 8019? Apollo DOMAIN 09-00-2B-00-00-00 6009? DEC MUMPS? 09-00-2B-00-00-01 8039? DEC DSM/DTP? 09-00-2B-00-00-02 803B? DEC VAXELN? 09-00-2B-00-00-03 8038 DEC Lanbridge Traffic Monitor (LTM) 09-00-2B-00-00-04 ???? DEC MAP End System Hello 09-00-2B-00-00-05 ???? DEC MAP Intermediate System Hello 09-00-2B-00-00-06 803D? DEC CSMA/CD Encryption? 09-00-2B-00-00-07 8040? DEC NetBios Emulator? 09-00-2B-00-00-0F 6004 DEC Local Area Transport (LAT) 09-00-2B-00-00-1x ???? DEC Experimental 09-00-2B-01-00-00 8038 DEC LanBridge Copy packets (All bridges) 09-00-2B-01-00-01 8038 DEC LanBridge Hello packets (All local bridges) 1 packet per second, sent by the designated LanBridge 09-00-2B-02-00-00 ???? DEC DNA Lev. 2 Routing Layer routers? 09-00-2B-02-01-00 803C? DEC DNA Naming Service Advertisement? 09-00-2B-02-01-01 803C? DEC DNA Naming Service Solicitation? 09-00-2B-02-01-02 803E? DEC DNA Time Service? 09-00-2B-03-xx-xx ???? DEC default filtering by bridges? 09-00-2B-04-00-00 8041? DEC Local Area Sys. Transport (LAST)? 09-00-2B-23-00-00 803A? DEC Argonaut Console? 09-00-4E-00-00-02? 8137? Novell IPX 09-00-56-00-00-00- ???? Stanford reserved 09-00-56-FE-FF-FF 09-00-56-FF-00-00- 805C Stanford V Kernel, version 6.0 09-00-56-FF-FF-FF 09-00-77-00-00-01 ???? Retix spanning tree bridges 09-00-7C-02-00-05 8080? Vitalink diagnostics 09-00-7C-05-00-01 8080? Vitalink gateway? 0D-1E-15-BA-DD-06 ???? HP AB-00-00-01-00-00 6001 DEC Maintenance Operation Protocol (MOP) Dump/Load Assistance AB-00-00-02-00-00 6002 DEC Maintenance Operation Protocol (MOP) Remote Console 1 System ID packet every 8-10 minutes, by every: DEC LanBridge DEC DEUNA interface DEC DELUA interface DEC DEQNA interface (in a certain mode) AB-00-00-03-00-00 6003 DECNET Phase IV end node Hello packets 1 packet every 15 seconds, sent by each DECNET host AB-00-00-04-00-00 6003 DECNET Phase IV Router Hello packets 1 packet every 15 seconds, sent by the DECNET router AB-00-00-05-00-00 ???? Reserved DEC through AB-00-03-FF-FF-FF AB-00-03-00-00-00 6004 DEC Local Area Transport (LAT) - old AB-00-04-00-xx-xx ???? Reserved DEC customer private use AB-00-04-01-xx-yy 6007 DEC Local Area VAX Cluster groups Sys. Communication Architecture (SCA) CF-00-00-00-00-00 9000 Ethernet Configuration Test protocol (Loopback) Broadcast Address: FF-FF-FF-FF-FF-FF 0600 XNS packets, Hello or gateway search? 6 packets every 15 seconds, per XNS station FF-FF-FF-FF-FF-FF 0800 IP (e.g. RWHOD via UDP) as needed FF-FF-FF-FF-FF-FF 0804 CHAOS FF-FF-FF-FF-FF-FF 0806 ARP (for IP and CHAOS) as needed FF-FF-FF-FF-FF-FF 0BAD Banyan FF-FF-FF-FF-FF-FF 1600 VALID packets, Hello or gateway search? 1 packets every 30 seconds, per VALID station FF-FF-FF-FF-FF-FF 8035 Reverse ARP FF-FF-FF-FF-FF-FF 807C Merit Internodal (INP) FF-FF-FF-FF-FF-FF 809B EtherTalk