BROCADE IP PRIMER

Chapter 1: Networking BasicsSwitches provide another wonderful advantage over hubs. They are capable ofsomething called full-duplex communication. This is the concept of transmittingdata and receiving data at the same time. We'll talk much more about thisa little later in the chapter.Layer 2 Ethernet (Addressing)Now we know how Ethernet is typically laid out physically. Let's talk more aboutthe protocol itself.MAC AddressWe talked about addressing in the Data Link Layer section. Ethernet uses a48-bit (6 byte) number to uniquely identify every physical device. This addressis called the Media Access Control (MAC) address. It is typically represented inhexadecimal (because writing out 48 1s and 0s makes for a very long number),and looks like this: 46:72:69:6E:6B:21. Different operating environmentsrepresent MAC addresses differently, but the number is the same. For example,Brocade represents the MAC address by separating it into two-byte pairs.The same number would be represented this way: 4672.696E.6B21.With 48 bits, you can represent over 281 trillion unique addresses. While thisnumber looks big and intimidating, there is a rhyme and reason to it. Theaddress is split into two 24-bit sections. The first 24-bits are assigned by theInstitute of Electrical and Electronics Engineers (IEEE). This 24-bit number isreferred to as an organizationally unique identifier (OUI). Every legitimateEthernet hardware manufacturer has at least one of these OUIs. Larger manufacturershave several. The second part of the address (the last 24-bits) is aunique identifier created by the manufacturer. It's the unique serial number ofthe device. This gives the company 16,777,216 unique addresses per OUI.46 : 72 : 69 : 6E : 6B : 21OUI Unique ID46 : 72 : 69 6E : 6B : 21So, if we take a look at an example MAC address, 46:72:69:6E:6B:21, we cansee that the OUI of the manufacturer is 46:72:69, and that the NIC's uniqueidentifier (assigned by the manufacturer) is 6E:6B:21. There are software programsavailable that will help you identify the OUI with a known manufacturer.This can be very valuable when troubleshooting problems on your network.28 Brocade IP Primer