DNARD Host ID EEPROM format
The DIGITAL Network Appliance Reference Design includes a serial EEPROM that contains the host identifier for the machine. The identifier is a sequence of 6 bytes (48 bits) assigned as a unique address in conformance with IEEE Std 802-1990 (also known as an 802.x MAC address, or more casually as an Ethernet address). The full address is denoted in this document as six bytes U-V-W-X-Y-Z, corresponding to network transmission order. (Since it is not useful to regard this byte sequence as a 48-bit numeric quantity, byte order is specified only for notational purposes, not numeric significance.)
To assign host IDs, manufacturers must:
The bytes U-V-W are the OUI assigned to the manufacturer and the bytes X-Y-Z are the unique identifier assigned by the manufacturer. Since this host ID is used to identify the machine on the network, great care should be taken to ensure its uniqueness (in particular, it must differ from the address assigned to any network interface cards, as well as being unique among NCs!). Note also that the host ID is always an individual address, rather than a group (multicast) address; this means that the first byte (U) is always even.
- obtain a 3-byte Organizationally Unique Identifier (OUI) from the IEEE
- allocate a 3-byte unique identifier to each board (i.e. just as with an Ethernet interface card). (See the IEEE tutorial.)
The EEPROM should be pre-programmed with the host ID. This is read by the firmware, and otherwise untouched by software (higher levels of the software stack should query the firmware to extract the host ID). Under no circumstances should this EEPROM be modified in any way by any level of software or firmware after the machine has completed the manufacturing process.The table below shows the EEPROM layout corresponding to host ID U-V-W-X-Y-Z.
- Bytes 0-5 and 10-15 contain the two copies of the host ID: the first in normal order and the second in reverse order.
- Bytes 24-31 contain two copies of a fixed "landmark" pattern, which serves to identify the ROM as a valid host ID ROM.
- All other bytes in the address range 0-65 are reserved.
Byte Contents 0 U 1 V 2 W 3 X 4 Y 5 Z 6-9 (reserved) 10 Z 11 Y 12 X 13 W 14 V 15 U 16-23 (reserved) 24 0xFF 25 0x00 26 0x55 27 0xAA 28 0xFF 29 0x00 30 0x55 31 0xAA 32-65 (reserved)
Updated: 11 September 1997
Copyright (c) 1997 by Digital Equipment Corporation
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