Routers and Hubs

Hubs
Hubs are dirt cheap and dumb as doornails.

Of course, this could lead off into a discussion of doornails. Frankly I have no idea what a door nail is, or why it is less intelligent than, say a 20-penny sinker. But apparently it is. You will have to go to home depot or someplace like that to explore this, as this is just a networking site. (I already tried AltaVista and it gave no significant information on doornails.)

Flash! The Doornail mystery has been cleared up, and I'm forced to take corrective action, viz,

The correct term is "Dumb as a doorknob", not "dumb as a doornail." There are however, doornails. They are big nails used to hold the door-jam in.

Are we done with this silly diversion now? YES!
Hubs are little tiny boxes with 4 to 24 RJ-45 connectors on the back that are used to connect Ethernet lines together. A hub is just a way to connect these lines in a "star" configuration, instead of daisy-chaining one to another. Daisy-chaining requires Ethernet interface adaptors that have one connection going to the computer and two for the network. They exist in coax and 10baseT (phone wire) form. With a hub, you just connect each computer to the hub, and the hub relays traffic among all the connected machines.

Daisy Chain of 4 computers (no hub):

    -------   ----------------   --------------
    |      |  |               |  |             |
    |      |  |               |  |             |
  +++++   ++++++             ++++++          ++++
  comp1     comp2            comp3            comp4

Here's a star connection of 4 computers:

          |     Hub     |
          ________________
    	/    |        |   \
       /     |        |     \
   comp1    comp2    comp3    comp4

Routers are smarter
A router, on the other hand, knows about types of traffic and destinations.

A router has at least two network connections: one to the local network and one to a remote network, or backbone. The purpose of the router is to "route" certain kinds of traffic between the two networks, and to NOT route certain kinds of traffic between the two networks.

This means that traffic between two computers on the same local network never gets onto the remote network or backbone. That keeps unnecessary traffic off the network, improving the performance for the traffic that does belong there. It also provides some security: traffic between local machines is not visible on the other side of the router.

So routers need to know at least:

• The range of addresses (IP or other) that are on the local network.
• How to access addresses (IP or other) that are NOT on the local network.

Typically routers have some other capabilities. Most have a hub built in, so you can connect at least 4 machines directly to the router using ethernet patch cables. Many routers are also specialized for making the connection to the WAN: that is, they are designed as an ISDN router or a DSL router or a Cable router (which is what a cable modem really is.) So in addition to the routing abilities, it has the ability to make a connection to the ISP over whatever network it is designed to work with.

A DSL router, such as the CISCO 675 has a phone line input for the DSL line, a "filtered" phone line output you can connect to a regular phone line, and 4 RJ-45 connectors to connect Ethernet to.

An ISDN router, such as a Netopia, has a phone line input for the ISDN line, two phone line outputs for the two regular analog phone lines you get with ISDN, and 6 RJ-45 connectors for computers.

Netopia Router

Since the router makes the connection to your ISP, it needs to know things like phone numbers to dial, accounts and passwords and such. Most of the difficulty in setting up a router is getting this stuff in correctly.

The IP information is covered fairly thoroughly in About IP.

----the Internet with millions of machines, all with unique IP addresses---
                              |
                              |
                 Your ISP and all their machines
                              |
                              |
              Your ISP's gateway - a specific IP address
                              +
                              +  (Cable Modem, ISDN, T1 or other link)
                              +
                 Your Router, with it's IP address
                              |
                              |
                  Your Hub (no IP address needed)
                          ___________
                          |  |   |  |
             all of your machines, each with their own IP addr.
                            

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