Differences between version 3 and predecessor to the previous major change of MAC.
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| Newer page: | version 3 | Last edited on Thursday, September 23, 2004 5:43:58 pm | by PerryLorier | Revert |
| Older page: | version 2 | Last edited on Thursday, September 25, 2003 12:28:41 pm | by JimCheetham | Revert |
@@ -8,7 +8,23 @@
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The term __MAC Address__ is also used to refer to the hardware address of an Ethernet card. These are usually hard-coded in an __Address [ROM]__ on the network interface card.
-A MAC address is 48 bits long, and is commonly represented as a colon-delimited sequence of 12 hex digits -
"mm.mm
.mm.nn.nn.nn
". The first 24 bits/6 digits identify the manufacturer of the network card, as overseen by the [IEEE] and [IANA]. See [http://standards.ieee.org/regauth/oui/oui.txt] for more information.
+A MAC address is 48 bits long, and is commonly represented as a colon-delimited sequence of 12 hex digits:"ab:cd:ef:gh:ij:kl
".
+
+The low nybble of the first byte (the
"b") contains a lot of information, the lowest bit of this means that the traffic is multiple destination (ie, multicast or broadcast)
.
+This is because on the wire each byte is sent low bit first.
+
+
The first 24 bits/6 digits (the "ab:cd:ef")
identify the manufacturer of the network card, as overseen by the [IEEE] and [IANA]. See [http://standards.ieee.org/regauth/oui/oui.txt] for more information.
A MAC address should be globally unique - no two network cards should ever have the same MAC address. Note that some network cards (notably, those used with Solaris machines) may be software-reprogrammable.
+
+----
+Recognising various mac addresses:
+* http://cert.uni-stuttgart.de/archive/intrusions/2004/01/msg00058.html
+
+Some common mac addresses you'll see (And get confused about):
+
+|1:0:c:cc:cc:cc|Cisco discovery Protocol (CDP)
+|1:0:c:0:0:0|Spanning Tree Protocol (STP)
+|1:0:c:0:0:0|Cisco Interswitch Link
+|1:0:5e:x:x:x|IP Multicast (RFC:1112)
