Cabletron Systems DMS-100 - Manual (Page 186)

186 Appendix I: Obtaining a MAC address
297-8991-910 Standard 03.01 August 1999
Figure 47 EIU MAC address format
The format of the MAC address is defined as follows:
• Nortel sets the two bits for the I/G and U/L fields according to the IEEE
definition of the MAC address.
• For the vendor identifier, Nortel uses the 22-bit identifier that the IEEE
assigns (00 0000 0000 0000 1010 1110). The convention used to represent
addresses in hexadecimal is to flip the bits in each byte end-for-end.
Therefore, the first three bytes of a single-station globally administered
address for an Nortel product in hex is 00 00 75.
• Nortel uses the System field to identify the type of product to which the
address applies. The hexadecimal value F identifies SuperNode systems.
• Nortel assigns in sequence the remaining 20 bits for the system-dependent
fields.
In summary, the first 24 bits of the address are defined by IEEE standards and
regulations. The remaining 24 bits are partitioned internally by Nortel to define
MAC addresses for its range of products.
EIUs are assigned 20 bits (greater than 1 million addresses) out of this range.
By convention, EIUs are datafilled with MAC addresses in a block of 16
addresses. This block must be unique among all SuperNodes deployed with
EIUs (65 384 unique values). The remaining four bits are also uniquely
defined to provide unique addresses within each SuperNode. Uniqueness is
enforced only within a SuperNode, not between SuperNodes even on the same
network.
I/G Nortel’s vendor ID System-dependent field
0
U/L
1 2 23 24
System
27 28 31 32 47
System
dependent
field