Which device should do PPoE: modem or TC?

al1776, welcome to the discussions!

BUT... my question is this. I've always had the modem in "bridge" mode with the Linksys (now the TC) doing the PPoE DSL authentication.

If you have a DSL connection as PPPoE implies, setting up the modem in "bridge" and PPPoE service on the TC is technically the correct way to handle things.

We see a substantial number of posts from users with connectivity issues...loss of signal intermittently...with the AirPorts that are setup to provide the PPPoE credentials. If there is a permanent "fix", I'm not aware of it.

Would you suggest that I set it up so that the modem (an ancient Speedstream 5100) does the PPoE instead? Might that be more stable for the TC?

If your old Speedstream allows you to setup the PPPoE service on the modem (I'm not sure if this model allows this), it might be worth trying. The "issue" here is that the modem will likely also supply NAT service. So when you connect the TC using "ethernet", +not PPPoe+, you'll likely see a Double NAT notice.

The Double NAT can range from being a very minor error to be ignored on a home network to a deal killer if you are trying to connect game consoles for interactive online gaming.

When my old Speedstream modem failed (can't remember the model), I replaced it with a Motorola 2210. I found that setting up the PPPoE service on the modem and connecting my AirPort Extreme using ethernet was a far more reliable way of staying connected, as opposed to configuring the modem as a "bridge" and setting up the PPPoE service on the AirPort Extreme.

Please keep us posted on your findings if you try the PPPoE service on the modem.

Bob, after reading many of your posts on the similar topics i thought i would try to ask you directly for your insights into my situation. Here it goes:

-Setup: ATT motorola DSL connected via ethernet to AEBS (N). AEBS connected via ethernet to iMac and PS3. iMac network set at manual DCHP address of 10.0.1.200. Multiple iPhones, an older iMac, a macbook, 2 macbook pros, and a pc all connecting via wireless to AEBS. 1 AEX connected wirelessly, configured to play iTunes to home stereo, 1 AEX connected wirelessly, configured to provide internt to a DVD player for Netflix streaming.

All worked 100% as expected for > 1 yr with very few problems. Occasioanly, the AEX to the DVD player would need to be unplugged and replugged as it would get droppped and the AEBS would blink amber.

Yesterday, I woke up to no internet service with the error reported from the AEBS that I have a Double NAT problem with a choice to either make it a bridge or keep it supplying NAT. If i choose the latter, i lose internet connectivity shorlty there after. If i choose brdige i get nothing. I have done factory resets several times and now when i configure it, i get forced to make this decision. In trouble shooting, i have unplugged both AEBS, turned off all the iPhones and only used one computer to work throught things. I have also turned my iMac back to DHCP vs Manual DHCP. (as i type this though, i forgot about my older iMac, which is probably still trying to connect)

I have checked my DSL modem and it is in PPPoE mode. I tried to change it to Bridge and again lost all connectivity, but was in a rush so I amy not have reset everything along the way probalby.

What is strange is that nothing i know of changed, but suddenly i get this error! The intial error was somethig to do with "the public IP address is already in use" and it asked me to change the ranges of the publick ip addresses.

Any thoughts how to get the DSL modem and the AEBS working consistently again?

thanks.

oops, my profile is old. Running on a 24 in iMac with 10.6.5. on all computers.

It sounds like you are using the Motorola 2210, but the product can vary a bit depending on where it is sold.

I would first power down the complete network. Wait a moment and start up the modem first and let it run for a few minutes. Plug the ethernet cable from the modem directly into your computer and make sure that you can open your browser and get a good internet connection. If yes, that confirms that the modem is working correctly and you can move to the AEBS.

If you want to use the modem with its current settings, you'll have to click "ignore" when you see the Double NAT message displayed from AirPort Utility. As I mentioned earlier in this post. Double NAT is a common network error, that can often be ignored on most home networks, to a real problem with some devices that require a different type of NAT setting to function correctly.

What is strange is that nothing i know of changed, but suddenly i get this error! The intial error was somethig to do with "the public IP address is already in use" and it asked me to change the ranges of the publick ip addresses

Haven't seen this one. Even if you wanted to, you can't change the range of public IP addresses, you can only change the range of "private" addresses on your
local network. These are the ones with the 10.0.x.x numbers.

Leave the iMac that is set for 10.0.1.200 off while you try to bring the rest of the network up. If everything looks good, then power up the iMac to see if it will connect correctly. Unless there is a specific reason that you have it set to connect at specific IP address, I would let it connect automatically using DHCP. Very few devices need a "fixed" IP address, so no reason to set that up if it's not needed. But, also no reason to change if it is working and you want it set up that way.

I think things work more reliably when the modem handles the PPPoE service, so I would try that first to see if you can get things going again. Sometimes, a simple complete power cycle will get everything back up when there has been an interruption in the Internet service. To do that, just power everything down, start the modem first, then the AEBS and devices all one a time waiting a moment or two for each device to power up.

Thanks for your follow up and the nice words! 🙂

Thansk Bob.. unfortunatley, i have done most of those things already. Will retry for 3rd time tonight. but more specifically:
-i have connected succesfully directly thru the modem via a laptop. no problems there.
-I have changed the imac to DHCP auto, stil get the same problem, everything works for about 5 minutes, then i get errors. If I hit ignore the double NAT, I then lose connectivity.
-I have powered everything down multiple times and in the proper sequence started them up, all to the same end point, errors.
-The only thing i havent done is hard reset the modem. That is what i will try tonight (if i can find my password for the ATT dsl set up!)

Could the AEBS being going bad? I have done factory resets on it multiple times. i have unplugged all cables and only connected via wireless from a macbook,and still get the same error.

Very strange behavior@@!

Thanks for your help!

One further question: If i have understood all your other great posts on the subject, to have a double NAT error, you typically have to have 2 sources of NAT going on. typically this errors seems to happen when cable or dsl modems are also routers, being paried to another router such as an AEBS.

In my case, their is ONLY the AEBS that has the DHCP /NAT, since my modem is NOT a router, only a modem... so where is the second one coming from that is causing the Double?

thanks.

If you have the Motorola 2210 or a similar device, it's hard to really know exactly what to call this device. It is technically a router or gateway because it does supply DHCP and NAT service.

But....the device only supplies one IP address.

So, if you connect it to another normal router, like one of the AirPorts, in order to have multiple devices connect, you must setup the AirPort to "Share a public IP address". The AirPorts supply DHCP and NAT service in this setting.

So, you have one layer of NAT coming from the modem and another layer introduced by the AirPort. The network now has a Double NAT.

If you put the AirPort in the technically correct setting....Bridge Mode....since the modem is only supplying one IP address, +only one device will be allowed to connect.+

I think the modem was really designed to make it easy for users to connect a single computer and get online quickly. It's easy to set up the PPPoE service on the modem and then all you have to do is plug into a computer and you are online. It you look at some of the setup pages for the modem by entering the 192.168.1.254 address, you'll see some notes about PPP service. There is a notation that PPP on the modem will work with "most" routers, but you may have to......etc.

The technically correct way to configure a router with this "modem" is to configure the modem as a simple "bridge" (it does not supply NAT service in this mode) and then setup the PPPoE service on the router, which supplies the NAT service. The Double NAT is eliminated this way.

So, there are two schools of thought here. One is to establish the PPPoE service on the modem because it is the device closest to the Internet connection. The other is to establish the PPPoE on the router and put the modem in bridge mode. There are plusses and minuses to each approach.

Message was edited by: Bob Timmons

I've looked for a Port Forwarding setting on the Motorola 2210 but never found it. Unless it's "hidden", I don't think the version that most people get will allow port forwarding to be configured. Will check again. Would be nice if the setting were there.

Network Address Translation is basically a "firewall" that protects devices on the local network (with "private" IP addresses) from the internet or "public" IP address at the WAN port of the main router on a network. It's very good protection.

Most of the time on most home networks, a Double NAT can be ignored. Actually when this happens, you are getting two layers of protection instead of one. Technically, I suppose this can slow things down a bit on a really large network with 50+ devices, but most home networks are much smaller than this...4-12 devices maybe.

Double NAT most often causes issues for online gaming consoles because they require a certain type of NAT to be able to work interactively with other gamers who are also online. That's why you see so many posts from Xbox guys who can't play online. They get a "strict" NAT notice when they try to set things up and can't figure out how to proceed from there.

Thanks Bob and Al. Very clear discussion. I did try to set up the motorola last night in Bridge mode but could not get it to work. But i did not make any changes to the AEBS in terms of changing any PPPoE settings. What are the settings that should be changed to coordinate with the Bridge setting on the modem? (I also ran out of time to really do a disciplined power down/up procedure, so will try again tonight)

But again, lastly, why suddenly am i having this problem? what could have changed and why? Previous to this, i simply plugged it all in and it worked! Now its become Plug& Pray...

So my game plan tonight is to:
1) shut down / disconnect everything.
2) try a hard reset on the modem, via a direct either net cable from a macbook at the right ip address.
3) Reestablish baseline connectivity to the internet on the macbook
4) disconnect the macbook, shut it down,
5) connect the modem to the unpowered AEBS, and doa factory reset on power up
6) restart the macbook and configure the AEBS wirelessly via Airport utility, using my past standard settings
7) see if things are stable, if yes, then....
8) connect the powered down iMac via ethernet to the AEBS, and reboot it, having previously set it to DHCPauto in network preferences
9) see if things are stable, if yes then....leave it alone for a few days
10) go back and add my DHCP manual address to the iMac. (for external access to the computer / files from a remote laptop etc, using dynDNS services for the modem I.P.)


If i fail at any of the above steps, i will go back and try to set the router on Bridge and the AEBS on PPPoE, following all the power down/up procedures.

Any further recommendations? THANKS!