network cisco ccna gns3 certification arteq

network cisco ccna gns3 certification arteq
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Wednesday, January 2, 2013

i/g u/g, msb and lsb...

this bugged me for about an hour last night and i was hoping i'd move on but it seems i'll have to post about it to get rid of it...


i/g individual/group

u/l universal/local

msb most significant byte/bit

lsb least significant byte/bit

and from what i've read cisco and ibm and others have differing opinions on the placement of these... of course this borders on networking esoterica and will probably never win you a bar bet...


that's wendell's take on it... the MSB is on the left, which is nice for me since i am an english speaking human and i read from left to right... things get a little hazy when the most significant bit is considered on the right of the most significant byte in the diagram above...

one of the great things about wendell is that he is tireless... while searching about this i came upon a document of his that addresses the ambiguity or confusion about this... here's an excerpt:,d.dmQ

It appears that some documentation, even from seemingly authoritative sources, will represent the I/G bit differently. In some cases, a doc references the bit as the lsb, and in others, the msb. In some cases, the I/G bit is shown on the left of a drawing or text representation of the first byte, and sometimes it's on the right.

But what matters? That when you type MAC addresses on Cisco routers and switches, and look at the output of show commands on the same devices, that the I/G bit is the rightmost bit in the leftmost byte, regardless of any other terms you use.

more significant than the significance of the bits is that this guy, in this document, has made a formal note to himself to address this issue in later editions of ccie r&s for clarity... it impresses me that he takes such care...

ultimately i'll go with wendell on this, but here are some others...

The most significant byte, also abbreviated MSB, is the byte in a multiple-byte word with the largest value. As with bits, the MSB (byte) is normally the byte farthest to the left, or the byte transmitted first in a sequence.
When the MSB in a sequence is farthest to the left (or first), the least significant bit or byte (LSB) is usually the one farthest to the right (or last). In this case, the sequence is said to be big-endian . If the order is reversed so the MSB is farthest to the right (or last) and the LSB is farthest to the left (or first), the sequence is said to be little-endian .

and scott morris here:

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