TechBasic Network Principles - A Supplement to BYOB #35

Basic Network Principles – A Supplement to BYOB #35

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In BYOB podcast #35 we talk about basic networking principles and some core concepts you should know about when building or working on your home network. Check out this short sermon while you are listening to BYOB #35.

Basic Network Principles – A Supplement to BYOB #35

You can download and listen to the show here

A NIC, a MAC, a Frame and a Packet walk into a bar…

A computer on your network is connected via a NIC, or Network Interface Controller. The NIC is the part of the computer where the network cable plugs in to. When your PC wants to send data, the NIC converts that data to a FRAME and sends the data through the cable. A frame consists of a Destination Address, a Source Address and then the data. In data networking, the concept of Media Access Control protocol, or MAC, provides a unique ID (or address) for each device. The address is 48-bit and symbolized by three, four hexadecimal groups. This address does not tell the actual location of your device, it just tells the unique MAC ID.

Basic Network Principles – A Supplement to BYOB #35

With these MAC addresses our NIC can create a frame. Once the frame is sent another NIC will see its own MAC address on the frame and then accept the frame also seeing the address of the sender. This is a very basic description but it suits us for the show.

If you are sending data to another network your NIC makes a packet. A packet is different than a frame in that it also includes the Destination and Source Network Address in addition to the MAC addresses. The one thing to note is that the MAC address will change as it goes across networks. The network address will stay the same.

Fast Ethernet

The Fast Ethernet was introduced in 1995. This standard is at 100 Mbit/s. Remember that when we talk Mbit/s that the number needs to be divided by 8 to get megabytes. For example, I get 30 Mbit/s download from my ISP which equates to 3.75 megabytes per second download. This conversion means that the highest theoretical speed in a 100 Mbit/s network is 12.5 megabytes per second. In reality you would be lucky to get 75% of that.

Gigabit Ethernet

Finalized in 1998, Gigabit Ethernet is the now becoming mainstream for desktop PC manufacturers and for home enthusiasts around the world. 1000BASE-T, as the copper wiring spec is known, actually uses all four cable pairs to transmit data in both directions. The speed of Gigabit is 1,000 Mbit/s which converts to 125 megabytes per second. Again, you will never get that max number and will settle for up to 80% or so.

Network Cabling

Cat 5e cable is used for Fast Ethernet although you can get away with using it for Gigabit. Cabling for Cat 5e can go 328 feet.

Cat 6 Cable is used for Fast, Gigabit and even 10-Gigabit Ethernet. Cabling for Cat 6 can go 300 feet while 10-Gigabit lengths are limited to 180 feet. This is more than enough for any enthusiast listening to this show.

Switches and cables all look the same so make sure you verify your equipment. In my network all blue cables are 100 while all yellow are Gigabit.

Basic Network Principles – A Supplement to BYOB #35

Switches

The switch is a multiport complex device that acts as a bridge at the MAC address level. Switches allow you to segment the network and allow for greater network capacity.

When the packet enters the switch the destination mac address the switch looks within the broadcast domain.

As I start talking about this keep in mind that there are two addresses. There is a Source MAC address and a Destination MAC address. Think of an eight port switch you can buy at Fry’s or BestBuy. You connect each device into a port. The switch keeps a table of the MAC address of each device. When you send a frame, the switch can do one of three things: Flood, filter and/or forward.

If the destination MAC is a broadcast address then the frame is sent to all ports except the sending port and this is called Flooding. Flooding also happens if the destination MAC address is NOT in the table.

If the MAC address is the same as the sender then there is no reason to forward it and this is called Filtering.

If the Destination MAC address is in the table the frame is sent to the proper port and this is called Forwarding.

Basic Network Principles – A Supplement to BYOB #35

Switching Methods

Store and Forward – Receives entire frame before switching and verifies addresses and error checks. Latency is an issue at times but this is going to be the most common for Linksys, Netgear and D-Link switches.

Cut Through – Starts as soon as it sees the MAC address. No error check so end device has to check.

Fragment Free – Receives first 64 bytes before forwarding, this prevents collisions.

The switch allows many workstations to transmit at the same time.

Basic Network Principles – A Supplement to BYOB #35

Routers

Expensive and setup intensive a router connects two or more devices on separate networks. Your router is what is needed to communicate with your ISP and determines the path when transferring data from one network to another. Your router will control access, port forwarding and other network specific settings. You can also have your router do policy-based routing which sets some rules for things like QOS for applications like VOIP and gaming apps. The main purpose of a router though is to connect your network to another network (internet) and forward packets to their destination. Routers do not care about the actual data in the packet and only look at the address. We heard last week though that you can build your own router and use software to create your own forwarding decision structure.

Basic Network Principles – A Supplement to BYOB #35

Listen to BYOB in the coming weeks for more information on networking!

Additional References

Cisco offers a good set of training documents for anyone looking for more information. The link will be in the show post.

http://www.ieee802.org/3/

http://www.cisco.com/E-Learning/bulk/subscribed/tac/cim/iprouting/basic_ip_routing_concepts/mod_frameset.htm

http://www.10gea.org/1000base-t/

Timothy Daleo

Timothy Daleohttp://usingwindowshomeserver.com
Timothy Daleo is a Project Resource Analyst and Oracle Applications Trainer in Pasadena, California. In addition to financial analysis, Tim has been developing training materials since 2003 and supporting direct projects through various auxiliary databases since 2005.

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