Help: Xfinity Internet slow speeds?

The late 2009 iMac does support Gigabit Ethernet.

Two things to check:

1. The Ethernet cable between the iMac and the Extreme. You should also test this with your MBP as well.
2. The Ethernet setting on your iMac. Go to System Preferences > Network > Ethernet > Advanced > Hardware tab. By default, the Configure option should be set to "Automatically." Check the Speed, Duplex, & MTU settings. If the connection between the Extreme and the iMac is full Gigabit, those settings should be (respectively): 1000bastT, full-duplex, & Standard (1500). Are they for yours?

using the Netgear CM600 for modem

Sorry you did mention it in your first post.. and once in the nitty gritty I forget some details.

CM600 should be fine. It is pure modem without any known interaction issues with the airport.

Wireless my speed jumped to 212.

Ok.. excellent.. this proves the first link is working fine.. modem to airport is clearly working at gigabit as you could not exceed 100mbps otherwise.

Although you can plug the Mac into the modem directly I doubt that will prove much. Might be worthwhile later.

What I would do is swap one of your upstairs airports for the one in the office..

Reset it to factory and do a new clean configuration.

Use all short names, no spaces and pure alphanumerics. Also use passwords with same rules.. but can be longer.

You will need to power cycle the modem due to change of router..

If this succeeds then the Extreme you used as router is faulty.. but might be ok upstairs extending wireless.

Went to main floor and then upstairs to 2nd floor to perform a speed test on my MBP.

It's a wireless connection on my MBP.

Speed hasn't changed, still 90s.

This is expected.. you are connected to an extender Extreme back to the Extreme that is still problematic..

If ethernet is used for the link, downstairs to upstairs.. then wireless might connect at high speed but the ethernet link slows it down.

Remember in research a negative result is disappointing but equally valid to positive result.

Pinpointing issues is based on lots of tests with the smallest number of components.

Did a speed test on my MBP and got 294.

This was wirelessly too.

Which indicates that the Extreme is working fine in terms of WAN connection and wireless is clearly good. It is just ethernet that is the problem.

You need something else with gigabit ethernet port.. I presume your MBP does not have ethernet? How old is it?

Would you be prepared to buy a thunderbolt to ethernet adapter? That would be a big help.

Or see if you can get a friend over with older Macbook that does ethernet.. or a PC laptop with gigabit.

We need to do the next bit of testing with a lot more numbers. And you need to check with some other device than your old iMac if the Extreme is somehow limiting the speed.

Assuming your modem is a pure or bridged type.. Just checked back.. yes it is CM600 .. straight modem..

To get internet to the iMac you need to shut down the modem for 10-20min during the disconnect time unplug the airport and plug the modem direct to the iMac.. start up the modem.. wait until all the light are working then start the iMac.. it should pickup an IP address and work.

I thought maybe there was a setting we could try first on the iMac to test.

If the iMac has stopped working at all.. as per your 0mbps .. then it has totally failed..

You should get at least 100Mbps but you really have to get 1000Mbps to have high speed.

Even if the iMac does not get internet the light on the modem or the airport should turn green when you plug in the iMac.. that is called connectivity light. Some modems or routers show speed by the color of the LED.. so green = gigabit and orange = 100Mbit.. The modem might show you this.

If you gain an Internet connection when you have them connected as follows:

Netgear > Extreme > iMac

... but not when they are connected as:

Netgear > iMac

The issue is that the Netgear is not "forgetting" that it is no longer connected to the Extreme. LaPastenague offered that you should power-down the Netgear for a number of hours. I would further suggest that you leave it powered-down overnight. Optionally, review the Netgear user guide to see how to reset this modem back to its factory default conditions.

The problem, as I see it, is with the Netgear. Replacing may or may not fix it. That is why again, I suggest that you work with a networking expert in your local area to help you get this working.

Is your iMac older? The only thing I can think of is that it doesn’t have a Gigabit ethernet port and only supports 10/100. Also, what type of Ethernet cable are you using?