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General discussion

Airport Express with wired networks

by therealcote Aug 23, 2005 2:22AM PDT

Hi,

It's now confusing to me as whether I can use an Airport Express as I would like to. Here's how:
I have a cable modem plugged into a wired router and two PCs plugged directly into my wired router.

I would like to know if it is possible for me to somehow plug the Airport Express to my router with an Ethernet cable and to have both a wireless and a wired network? Or can I divide my Ethernet cable coming out of my cable modem so one end goes into my wired router and the other end goes into the Airport Express?

Thanks a lot
Mathieu

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3 Posts
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how it works...
by Dick White Aug 23, 2005 4:31AM PDT

Let's start at the end of your question and work backwards. You cannot "divide" an ethernet cable like you would an electric extension cord or a telephone cable. The ethernet cable is point to point, with different things going on with the several different little wires inside. So we can just let go of that idea.

Your wired router has 4 ethernet ports on it (or at least most common ones do, you didn't say exactly which on you have...). You have 2 PCs plugged in there, leaving 2 open ports. Yes, if you use another ethernet cable from the port #3 on the router to the Airport Express, you will now have a wireless network running in the airspace around your wired network, and if you configure the Airport Express properly, the wireless devices that might come into the room and connect to the Airport Express will indeed be part of the same overall network that includes your wired computers too.

dw

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Thanks
by therealcote Aug 23, 2005 8:05AM PDT

Thanks a lot

This is what I thought at first but then I read something on the web suggesting that I couldn't plug an Ethernet cable from my router to the Airport Express.
Final and dumbest question: does an Ethernet cable is the same type of cable (RJ-45) that I'm using right now between my router and my PCs?

thanks again for your help
Mathieu

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...welcome...
by Dick White Aug 23, 2005 10:06AM PDT

hmmm, I can't imagine why anybody would think you can't plug in an ethernet cable from the router, especially when the bottom of page 7 of this document from Apple says that's how you do it...

Yes, an ethernet cable is the same kind of cable you are already using. The terminolgy "RJ-45" refers to the standard size and number of pins on the connector on the end of the cable. "Ethernet" refers to the networking methodology. When ethernet is implemented using an unshielded twisted pair (UTP) topology (as opposed to coaxial or thin-net), RJ-45 connectors are assumed. Thus, in the marketplace you might see the terms used interchangably, though that is not technically correct. A nuance to be aware of when shopping, ethernet patch cords can be wired either as standard straight through or cross-over. Each has a specific use and usually will not work when the other type is called for. You will need a standard straight through cable. If the bag says cross-over, put it back on the rack and look down the row for a straight through. If it does not specifically say cross-over but doesn't say anything else, it is presumed straight.

Another nuance when setting this thing up in your configuration. The Airport Express is a very robust little device. It can operate as a full-featured wifi router complete with DHCP services, as well as just a plain access point. Your existing router is currently doing the DHCP service for your (wired) network. It should also do so for the new wireless portion being established by the Airport Express. That means you need to configure the Airport Express during the setup process to NOT do another layer of DHCP for the wireless part only. If that were to happen, a wireless client could still get to the internet, but it would be operating on a different subnet from your wired systems and thus you would not be able to transfer files between wired and wireless systems or share printer resources between wired and wireless. So.... turn off the DHCP in the Airport Express when you set it up.

dw

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