2.1.a Implement and troubleshoot switch administration

i/g u/l

i/g means individual/group, u/l means universal/local. examine the mac diagram below:


msb is to the far left (1st byte), while lsb is far right (6th byte). the first three bytes comprise the organizationally unique identifier and the last three bytes comprise the vendor assigned unique value to round out the complete address. this is mandated by the ieee.

we know the mac is 48 bits or 6 bytes.

the 1st bit of the 1st byte (left to right) is considered the most significant bit. the last bit of the 1st byte likewise is the least significant bit. when the frame is transmitted the expected order is 1st byte 1st and so on, however the bits of the individual byte are transmitted in reverse order. this is often referred to as canonical (authorized; recognized; accepted as standard).

if the i/g bit is set to 0 it is a unicast address; if it is set to 1 it is either a multicast or broadcast.

if the u/l bit is zero the mac has been assigned by the vendor; if it is 1 it has been locally assigned (administered), which overrides the original assignment by the vendor.

now consider this address: (from pearson it certification test, ccie v5)


An Ethernet MAC address is always written out in the big endian order, most significant byte first, and is also transmitted on the wire in this order of bytes. However, individual bits of each byte are transmitted in the reverse order, starting with the least significant bit (as stated above). The first byte of the MAC address to be put on wire is 0x03, or 00000011 in binary. In this byte, the least significant bit, or the rightmost bit, is the Individual/Group (I/G) bit, currently set to 1, thereby indicating this is a group MAC address (multicast). The second least significant bit is the Universal/Local (U/L) bit, also set to 1, indicating that this MAC address is locally administered and has not been allocated by IEEE. The bits of the first byte will be transmitted as 1-1-0-0-0-0-0-0 (note reversal). In this sequence, the first transmitted bit is clearly set to 1. (it would be unicast if zero)