Friday, September 06, 2002
Layer 2 refers to the Data Link layer of the commonly-referenced multilayered communication model, Open Systems Interconnection (OSI). The Data Link layer is concerned with moving data across the physical links in the network. In a network, the switch is a device that redirects data messages at the layer 2 level, using the destination Media Access Control (MAC) address to determine where to direct the message. The Data-Link layer contains two sublayers that are described in the IEEE-802 LAN standards:
Media Access Control (MAC) sublayer
Logical Link Control (LLC) sublayer
The Data Link layer ensures that an initial connection has been set up, divides output data into data frames, and handles the acknowledgements from a receiver that the data arrived successfully. It also ensures that incoming data has been received successfully by performing an error checking routine called a CRC (Cylic Redundancy Check).
Media Access Control (MAC) sublayer
Logical Link Control (LLC) sublayer
The Data Link layer ensures that an initial connection has been set up, divides output data into data frames, and handles the acknowledgements from a receiver that the data arrived successfully. It also ensures that incoming data has been received successfully by performing an error checking routine called a CRC (Cylic Redundancy Check).
Layer 2 Hardware Addresses
The Media Access Control (MAC) addresses used by Ethernet (802.3), WiFi (802.11b) Token Ring (802.5) and FDDI (802.6) take the form of a 48 bit binary value expressed as 12 hexadecimal digits. An example is: 00-50-56-C0-00-08
The first six digits are the Organizationally Unique Identifier and typically indentify a manufacturer of network hardware. The addresses are dispensed by the IEEE . You can find a searchable index of OUI's here.
The Media Access Control (MAC) addresses used by Ethernet (802.3), WiFi (802.11b) Token Ring (802.5) and FDDI (802.6) take the form of a 48 bit binary value expressed as 12 hexadecimal digits. An example is: 00-50-56-C0-00-08
The first six digits are the Organizationally Unique Identifier and typically indentify a manufacturer of network hardware. The addresses are dispensed by the IEEE . You can find a searchable index of OUI's here.
Thursday, September 05, 2002
Nerds 2.0.1 and Triumph of the Nerds are two great PBS shows about the history of modern computing and the development of the Internet. If you have kids or if you simply enjoy decent television, you should check these shows out.
If you wish to understand the history of the development of TCP/IP, read the Internet Timeline
Daryl's TCP/IP primer.
Introduction to TCP/IP.
Charles Spurgeon knows an awful lot about Ethernet.
Here is a link to an IANA "well known ports" document. This will tell you which services are associated with which TCP and UDP ports.
Ethereal is one of the best graphical protocol analyzers available.... and it runs on nearly any OS... and it's FREE!
Tuesday, September 03, 2002
Here is a link to an older "how to set up a simple network" document.
