Networking & Security FAQ

Anti-Trend

Networking FAQ

Q: What's the difference between a hub, a switch, a router, and a firewall?

A: Hubs, switches, routers and all have the same general purpose, which is to provide network connectivity. However, they are all very different network appliances. The hub is the dumbest of the group; all it basically does is physically connect several network devices together. Since a hub does not provide any switching or buffering features, there are many data collisions (especially on busier networks), which results in much lower data transfer rates than might be achieved. Hubs are depreciated technology, and are rarely seen in the field anymore. A switch is much like a hub, in that it also connects multiple network devices together. The important difference is that the switch provides switching, which is basically a form of traffic management, much like a traffic signal. This virtually eliminates data collisions, effectively increasing data throughput by cutting back the need to send the same data multiple times due to packet loss. Switches also feature memory buffers of various sizes, which further increase transfer efficiency. In terms of home networking, router and firewall are almost synonymous terms -- except in the case of software firewalls, which run on the client computer rather than in hardware. Routers/firewalls handle packets which are being sent to and from different networks, sending them along the proper routers so they get to their destinations, and forcing them to obey rules which are set by their administrators. If a switch is a traffic light on a network, a router would be a traffic cop. They are primarily security appliances, which prevent unauthorized access while allowing approved traffic to pass through unabated. Wise people will be noted to have routers between their local networks and the Internet (see the Security FAQ for further security information). A managed switch is a device which has properties of both a router and a switch in that an administor can manage traffic on a per-port basis. This is useful on large networks where extra control is needed.

Q: What's the best way to share a broadband connection or create a home network?

A: I unreservedly recommend purchasing a router. There are routers in the sub-$40 range which offer strong security capabilities and even have integrated network switches. In other words, you can have a pretty good network solution for very inexpensive and almost zero setup time. I don't recommend Windows ICS (Internet Connection Sharing) as a method for sharing broadband, as it has several fundamental flaws and security problems. Besides this point, it's actually more troublesome to setup than a real router. If you're the do-it-yourself type, check out the excellent IPCop. You can build a powerful, easy to use router out of an obsolete PC at virtually no cost, since the software portion is 100% free!

Q: What is the difference between Cat3, Cat5, and Cat6 cables?

A: The "Cat" in "Cat5e", for instance, is short for category. The number in the designation stands for the grade of networking capability that particular cable is capable of. Higher numbers are higher grade. For example, Cat3 is the type of cable most typically used for broadband internet connections such as ADSL and in-wall phone lines. Cat5e (e = enhanced) is the most commonly seen type of networking cable used in home & office networks. What many of the "Cat" cables have in common is that they're made up of UTP; that is, unshielded twisted pair. This type of cable is fairly light gauge copper sheathed in a light plastic such as PVC, which is very inexpensive to deploy. Since it relies on its own built-in redundancy to cancel out interference, it doesn't need bulky and expensive insulation to shield it. Here's a quick, non-comprehensive table of cable categories and their respective typical transfer rates:

Category:..........................Speed:..........................Usage:
Cat1......................................Up to 1Mbps.....................Analog voice; Doorbells; etc.
Cat2......................................4 Mbps.............................IBM Token Ring networks
Cat3......................................16 Mbps...........................Voice or Data; 10BaseT
Cat4......................................20Mbps.. ..........................Token Ring; Not often seen
Cat5......................................100Mbps. .........................Depreciated Ethernet
Cat5e....................................200Mbps (Full-Duplex).......Standard Ethernet
Cat6......................................Up to 400Mhz...................Network Backbones; Gigabit
Cat7......................................600-700Mhz......................Proposed Network Standard

Q: What is a crossover cable? What are they used for?

A: In network cabling, there is often more than one way to wire the connector jacks at the ends of the cable. For instance, with Cat5 cables, there are two which are commonly used: type A and type B. Type A cables place the green pair on the outer edge of the jack and the orange pair around the center. Type B is the opposite, with orange on the outside and green around the center pair. Normal patch cables utilize one standard or the other. A crossover cable uses a type A connector on one end of the cable and a type B on the other. The gist of it is that the pair of wires that send and the pair that recieve are opposite on each end so that both ends are not trying to send through the same pair. This configuration is typically used to directly connect non-switching network devices, such as PC to PC (with no hub/switch), router to router, etc. Some modern switches and routers feature auto-negotiating ports, which sense if the connection needs to be a crossover and adjusts for this on the fly. However, many devices still require crossover cables in order to uplink to another device.

Q: What does "TCP/IP" stand for? What about "UDP"?

A: TCP/IP stands for Transmission Control Protocol over Internet Protocol. It's basically the standard language for networking communication, and was established by DARPA long before "Internet" was a household word. Many different protocalls run on top of TCP, for example HTTP (which is providing the website you're viewing now). One of the unique things about TCP which makes it so popular is the way traffic is handled. Basically, start and end bits are needed on each transmission to make sure the data was sent and in turn recieved properly. UDP stands for User Datagram Protocol. Since UDP does not have the data safeguards found in TCP, it is used for some important networking functions (Notably DNS), but only a scant few of these involve the transfer of large amounts of information. The exceptions include some games, which typically make use of UDP due to the fact that it's faster than TCP (and games are considered less-than-critical data transfer).

Q: What is "ADSL"?

A: ADSL stands for "Asyncronous Digital Subscriber Line". It's a method of sending digital information over your standard copper phone lines. ADSL subscribers can achieve very high download speeds but upload is substantially slower, hence the 'asyncronous' designation. One of the nice things about ADSL is that although it runs over your standard copper phone lines it does not tie up your phone like dialup. Because it avoids using the small frequency range that voice transmition uses, you are free to use your phone normally while you download large files simultaneously.

__________________
See My Desktop | Try Linux | Install Linux | Visit My Server | Support Hardware Forums | Easily rip DVDs in Linux | Remember Everything