Strange IP address issue

C

Chris Behm

Registered
Hi there,

I currently just moved into a new apt. I had to switch ISP's, given the old ISP wasn't available in my new neighborhood. My set up is a 15" Powerbook G4 1.67 ghz model, currently running OSX 10.4.8. I have an airport express involved in the picture, as well as the usual comcast motorola surfboard cable/broadband modem.

Here is my issue, when comcast came out to do the installation, I was not able to get a dynamic IP address using DHCP while connected via ethernet. I tried everything in the book to get that modem to kick a dynamic, restarted the modem, restarted the Powerbook, powercycled the modem for 15 mins, lit a candle and prayed to the gods, sacrificed a live chicken etc etc... it just wasn't happening. So, the smug comcast tech goes to his truck to grab his windows laptop, he plugs in and gets online no problem without any configuration what so ever. I was completely embarassed to say the least. How is this possible, I thought macs were far more superior and simple?:confused:

After the tech left my apt, I decided to grab my airport express, I planned on using it with the set up anyway. I plugged it in the wall socket and then plugged the ethernet cable in, next thing I knew, I was getting a dynamic IP no problem. I scratched my head and thought how is that possible? How am I getting a static when wired directly, and a dynamic when I am using a wireless router? Usually, in my experience, its always the other way around. As I am writing this, I am still not able to connect via ethernet only through the airport express. This is something that is just frustrating me to no end. I just want it to work! I am one of those kinds of people that even though I will probably never use the ethernet port to connect to my network as long as the express is working, I just need to know that I CAN get it to work. I am including screen shots of my airport express config as well as the ethernet config. Can someone please help me get a dynamic IP via ethernet it is bugging the crap out of me.

Thanks,
 

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It looks like what you have been provided with is, like you say a modem and as such is not capable of routing as it does not handle routing.

When you connect the airport express which is a router the problem is resolved. I am not surprised his laptop worked as it will have been specifically configured and tested with the kit before he came out.
 
so, does that mean that I have a bad modem from comcast? I'm not really clear on what needs to happen to make this work. Just for the record, I checked my ethernet port at work today and I got an IP in literally miliseconds via ethernet. How do I get this thing to work?
 
This is almost definitely not the problem, but there's a remote possibility the router isn't recognizing your laptop's MAC address for some reason. That would be highly unusual, but not impossible to imagine, since cable ISPs used to limit access to any particular modem by MAC address.

There's a remote possibility that your MAC address is being blocked at the ISP. That would be crazy, but crazier things have certainly happened. It's worth a call to their support people, if you have that kind of time.
 
What exactly does that mean? As far as I know comcast only offers the one modem that they issue you. I'm not going to go out and spend money on a modem. What if I didn't have my airport express and couldn't get online period. What would they do for me? Would I be stuck without internet? This whole situation is just weird. Can someone offer anymore input? To everyone that has attempted to help me out, I do appreciate your kindness. I support macs for a living so I am not a newb, I know what the issue is, I usually know how to resolve it instantly ie: powercycle, check using dhcp and renew dhcp lease. However, none of these have worked. Is there a way to reset the mac address on my powerbook so that it accepts the mac address from the modem? If so is this going to screw up my current solution of the airport express connection? Anyone else have anymore suggestions? I am really freaking out about this! Its become a pride issue now.
 
The only other possibility I can think of, which would be just as strange as the MAC address blocking possibility I mentioned above, is that your firewall is on, and somehow set so restrictively that you can get a DHCP address broadcast from the modem. Again, highly unlikely. But if your firewall's on, just for sh*ts and giggles, try turning it off.
 
I only know how it's handled with Cablecom, one of the Swiss cable providers. They restrict the amount of devices that can connect, i.e. how many devices can get an IP from their servers. If that limit is "1" or "2", that would explain your situation, maybe. His laptop got an address, then your AirPort router. Now if you connect through AirPort, you get an IP from _that_, not directly from Comcast. If you, however, connect directly, your notebook wants to get an IP from Comcast, which - if the limit of given IPs is reached - will be denied.

When I was working support for Cablecom, we usually told customers complaining about that to reset their cable modem completely, which should - at least - clear the MAC-address list from the modem, although the same list could also be kept on the cable-co's servers. We usually cleared that list anyway, if a customer called about such a problem.
 
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