Something I've never seen before

[DoYouKubuntu]

You'd think that after 100 years in computing, one would've seen it all, right? Wrong! Here's something I've just come across--and I'm scratching my head.

I plugged my [still quite new] System76 laptop directly into my cable modem--and had *NO* Internet. Double-checked...yes, this REALLY is the Ethernet cable FROM the modem that normally goes TO the router...so it's going FROM the modem TO the laptop...nothing.

Laptop shows hardwired connection.

Reboot modem.

Nothing.

Could the port on my [still quite new] System76 laptop be bad? *goes to bedroom, grabs Chromebook*

Unplug Ethernet cable from S76 laptop, plug it into Chromebook.

Chromebook shows hardwired connection.

NOTHING.

Reboot modem.

NOTHING.

Take Ethernet cable out of CB and plug it back into my router.

Activate wireless connection on S76. Voila! Internet.

Ditto for CB.

WTF?!!!

Anyone? Does anyone have ANY clue what the BLANKETY-BLANK it is that I'm seeing?! Because I don't.

To summarize:

- A 4(?) foot long Ethernet cable when plugged into the modem and router yields perfectly good Internet connections, both wired (some of my desktops, which I didn't mention above, are hardwired to the router) and wireless.

- That same cable, when taken out of the router and plugged into either of two laptops, yields NO Internet connection.

I did NOT try a different cable. But I don't see why I should need to, considering the cable in question works just fine when connected to the router--plus it would be a hassle to find and try a different one!

[Rod J]

I think it could only be that the cable is faulty. A bad connection somewhere in the wiring ... sometimes it works, sometimes it doesn't.

[life0riley]

Your router is broadcasting a MAC address. Your ISP saw that when they helped you connect. The MAC address of your router is not the same as the MAC address of the laptops you connected directly to the cable modem. Your ISP is expecting the MAC address your router is broadcasting.

[DoYouKubuntu]

I've already taken my sleeping pills, so if this is incoherent, well, just laugh it off!

I think it could only be that the cable is faulty. A bad connection somewhere in the wiring ... sometimes it works, sometimes it doesn't.

I don't know...I mean, I know that kind of makes sense, but:

- works 100% of the time if connected to modem
- fails 100% of the time if connected to a computer

I just don't know.

Your router is broadcasting a MAC address. Your ISP saw that when they helped you connect.

I thought the only MAC address they saw and/or cared about was that of the new modem.

The MAC address of your router is not the same as the MAC address of the laptops you connected directly to the cable modem. Your ISP is expecting the MAC address your router is broadcasting.

Okay, so then...what? I've hardwired a laptop directly to a modem before, and don't recall any issues like this.

[life0riley]

Something I've never seen before

It's a new modem and you had to call them to get a connection.

I had a similar experience when I connected my new modem. I had to call Comcast initially to give them the MAC address of my new cable modem. They told me to connect my computer first to get a connection and get online. When that was done I connected my router to my new cable modem and connected my computers to the router, but I couldn't get on the internet. I had to log into my router and set it to broadcast my computer's MAC address. Once I did that I was able to get online with all my devices through the router.

That's how it works with my ISP. This is my best guess based on my own experience with my new modem.

[DoYouKubuntu]

I had a similar experience when I connected my new modem. I had to call Comcast initially to give them the MAC address of my new cable modem. They told me to connect my computer first to get a connection and get online. When that was done I connected my router to my new cable modem and connected my computers to the router, but I couldn't get on the internet. I had to log into my router and set it to broadcast my computer's MAC address. Once I did that I was able to get online with all my devices through the router.

I started wondering if there was something I needed to edit/tweak in my router's settings, but then realized that's NOT the problem and to forget about it! It's when my router is taken OUT of the equation that I'm not getting an Internet connection. So it's kind of the opposite of your experience. In my situation, I don't see...well, I just don't see!

[SteveRiley]

In Seattle at least, Comcast:

• does not check MAC addresses of devices attached downstream of the modem. Thus, any device plugged into the modem's LAN port(s) would have Internet access.
• does not require any form of authentication sequence (like account ID/password) configured in devices attached downstream of the modem.

If this is also true for your area, then I think it's time to call your Comcast support line.

Wait... when your router is attached, how do your PCs obtain IP addresses? If DHCP, then your PCs are likely obtaining IP addresses from your router. If you attach your PC directly to the cable modem, you should receive an address from Comcast. If you're using static IP addresses in your with-router setup, then you must change that on the PC you're connecting directly to the modem.

[DoYouKubuntu]

In Seattle at least, Comcast:

• does not check MAC addresses of devices attached downstream of the modem. Thus, any device plugged into the modem's LAN port(s) would have Internet access.
• does not require any form of authentication sequence (like account ID/password) configured in devices attached downstream of the modem.

If this is also true for your area, then I think it's time to call your Comcast support line.

(It's Time Warner/Earthlink.) That's the same for me--Time Warner only needed information regarding the new cable modem, i.e., its MAC address, and that was that. They activated it and I was off and running.

Wait... when your router is attached, how do your PCs obtain IP addresses? If DHCP, then your PCs are likely obtaining IP addresses from your router. If you attach your PC directly to the cable modem, you should receive an address from Comcast. If you're using static IP addresses in your with-router setup, then you must change that on the PC you're connecting directly to the modem.

I've assigned static IP addresses to all of my computers. So, for example, the laptop I'm typing on right now: its address is 192.168.1.123; it's connected via wireless. When I hardwire it to the modem...?

[SteveRiley]

I've assigned static IP addresses to all of my computers. So, for example, the laptop I'm typing on right now: its address is 192.168.1.123; it's connected via wireless. When I hardwire it to the modem...?

Bingo. That won't work when your computer is directly connected to the modem. You need to switch the computer to DHCP and let it take an address assignment from your ISP.

[DoYouKubuntu]

Bingo. That won't work when your computer is directly connected to the modem. You need to switch the computer to DHCP and let it take an address assignment from your ISP.

Is it okay if I blow you a kiss, Steve? Mwaaaah!!

I'm way too lazy to lug any of my laptops over to the modem right now, but I strongly suspect the problem will now be solved. When the laziness wears off, I'll post the results.

[SteveRiley]

Is it okay if I blow you a kiss, Steve? Mwaaaah!!

May I have two, please.

[DoYouKubuntu]

May I have two, please.

Mwaaaaah! Mwaaaaah!