MTA exam question

[netsider]

I know this is just basic fundamentals of networking, but I'm getting a little confused. In most of the resources that I have (for the MTA exam, anyways), it states that a router connects networks and determines the best path for a packet to take to reach its destination (hops). "Routers track subnets, not individual computers" - Okay... simple enough, I get it. BUT!:

What is confusing me, is the fact that I have a router for my cable modem, which acts as a switch for multiple computers in my house. If I were to use a hub, there would be collisions... which insinuates to me that it's helping direct the traffic of the other PC's in my household (obviously).

Since all of the computers in my house are on the same subnet, and if a router isn't responsible for directing traffic from multiple computers... what offers an explanation for the router I have in my house, acting without a hub or switch? If a router only tracked subnets and routes, then how would someone be able to use a router (which you can), to act as a hub/switch for your home network, even when there isn't internet involved at all?

Do I have a router, with a built in switch, or something? I understand a lot about networking without effort... but this is almost contradictory. Basically, a router can be used in place of a hub or switch, with or without internet, to connect multiple computers. That's a given.. I've done it, and mostly anybody involved in networking has done this. Why, for the purpose of the exams, does it seem to want you to not think of a router in terms of connecting individual computers together?

Any help would be appreciated... and sorry for the long explanation... just wanted to make sure I was making a clear statement. Thanks guys!

 

[gimp]

Don't use regular consumer hardware as an example.

Your off-the-shelf consumer router also has a built-in switch. The 4+ LAN ports are actually a switch. The routing is really only done through the single WAN port.

 

[/usr/home]

Think of a home grade router or even an all in one from your ISP as the modem, router, and switch. They are three physically different devices, but on one PCB. The router only routes between networks, the switch only forwards packets out of the appropriate ports, and the modem only converts analog to digital. They are all just in one device.

 

[Protoform-X]

Yes, your router has a built-in switch. Almost all consumer routers have built-in switches. You'll notice on enterprise routers that they typically only have 2 or 3 ports- Generally these are ALL layer 3 routed ports, where the consumer router is only routing traffic from the layer 2 switch ports through the WAN port.

Routing is needed any time you change subnets. So say you're on the 192.168.1.0/255.255.255.0 subnet and you want to get to google.com which happens to be on IP 74.1253.224.167 for me today. The computer will need to send the packet to it's gateway, the router, for that packet to find it's way. The only network the computer knows about is the 192.168.1.0 subnet, and it'll send all other packets to the router. All 192.168.1.0 packets only hit the switch; they'll never hit the router.