Help: Xfinity Internet slow speeds?

When you test.. do not plug the upstairs into the Extreme at first..

Just use modem to wan port of the AE.. and Mac to LAN port of AE.

As Tesserax indicated already ensure the connection is gigabit.

You can also use network utility which Apple has now hidden.. just use search in finder.

Click on info and you will see the connection speed.

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?

100Mbit/s is what I got on my iMac using Network Utility

I would like for you to do the following:

1. Power-down the Netgear gateway, the AirPort base stations, and your iMac. Order doesn't matter.
2. Connect a single Ethernet cable between the Netgear and the iMac.
3. Power-up the Netgear. Give it about 5 minutes to initialize.
4. Power-up your iMac. Leave the AirPort base stations powered off.
5. Using the Network Utility, what is the Link Speed read now? Is it still 100 Mbit/s or 1 Gbit/s?
6. If it is still 100 Mbit/s, either the Netgear, the cable, or the iMac's Ethernet settings is faulty/wrong.
7. If it is 1 Gbit/s, then power-down the Netgear and iMac. Again order doesn't matter.
8. Now connect your "main" AirPort base station to the Netgear, using the Ethernet cable that was connected to the iMac. Connect a second Ethernet cable between one of the available LAN (opposing arrows) ports on the base station to your iMac.
9. Power-up the Netgear, wait at least 5 minutes for it to initialize.
10. Power-up the AirPort base station, wait until its status LED is a solid green.
11. Power-up the iMac.
12. Again, use the Network Utility. What is the Link Speed now?
13. Did it drop back down to 100 Mbit/s or is it now 1 Gbit/s?

At this point there should only be the Netgear and the iMac connected by Ethernet. If you are getting zero for the link speed, the only possibilities are:

1. The Ethernet port on the Netgear is faulty,
2. The cable is faulty, or
3. The Ethernet port on your iMac is faulty.

Two things from your image:

1. The iMac is not getting an IPv4 address from the "modem." It should get one whether it is performing as a router or as a simple modem. This could be that the "modem" is incorrectly configured or that you did not allow sufficient time to allow it to "forget" the previous device (the Extreme) that was connected to it.
2. I've never seen Apple use NVIDIA chipsets for their Ethernet port. I would have expected that it would be some variation of a Broadcom chip. Has this iMac ever been repaired? ... and if so, was it done by Apple or an Apple Authorized Service Provider or by some other third-party repair facility?

Shouldn't my speeds be higher than 90s I'm getting?

Ethernet that is damaged or incorrectly installed or cables made up badly will either not work at all which would be easy to detect.. or they work at 100Mbps.. which would give your 90Mbps speed.

Tesserax is asking the right question. Somewhere you have a badly installed cable.

On the iMac .. which I gather is in the same room as the Extreme that is working as router.. try using wireless instead of ethernet and give us a speed.

If that gives you high speed..

I would disconnect the Airport working as main router and plug the computer directly into the modem.. you will most likely need to power cycle the modem.. off for 10-15min is enough but can be longer.. and then get the speed.

Exactly what model of modem are you using..

Something does not make sense because if wireless on iphone etc is so fast.. I see no issue between the modem and the airport.. yet all your system appears to be slowed down once ethernet is involved.

Another test that is worth performing since you have three airports.. swap one of upstairs one with the router.. reset it to factory and use a different configuration name etc.. basic as possible.. and see how it goes.

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.