Cable modem newbie questions

Hardware and technical stuff
1

OK, I’ve just gotten connected to my new cable internet service with Comcast (they gave me a pretty great deal), and I have a couple of questions. Right now, I’m overlapping the service with DSL because I just want to make sure I get everything working properly with the new service first.

1st question: currently my wireless router is working as a wireless access point only, and it’s hooked up to my DSL modem/router, which is doing the DHCP and all that. What’s the best way to make the change in its configuration (i.e. make it act like a router again) so I can move it over to the cable modem (a Cisco 2100), which I understand is purely a gateway? Would the easiest thing to do be to hit its factory defaults button? Or access its configuration screen, turn on DHCP, and go from there?

2nd question: right now the cable modem is only hooked up to my main desktop machine, via ethernet cable. Am I currently behind any kind of firewall besides Windows firewall, or am I nakedly exposed to the big bad world?

That finally leads me to the third question: is there any configuration screen I can access for the cable modem itself? If so, at what IP address? What’s the default for Comcast provided cable modems?

Thanks for any and all help and for taking pity on a cable internet newb (I’ve only ever had DSL before this). José aka Papageno

2

To find the IP address, go to your command prompt and type ipconfig /all. If you’re wired straight to your modem, the gateway address should be the address for your modem. Not sure how much you can do, and I assume you’ll need a username and password. You can probably google the modem’s model number to get that info.

3

Weird, when I type in the “default gateway” address in the browser, I just get a “the connection to the server was reset while the page was loading” error in Firefox.

4

That is weird. Maybe the modem’s not reachable via HTTP. Is there a USB port on it?

5

I’ll double-check later, but I’m pretty sure there isn’t one. What I remember seeing was just the coax connector, the ethernet port, and the power connector.

6

Hey that was a fast switch, grats :)

  1. You’re basically on the open internet. Comcast used to do some port blocking (myself and a couple coworkers had to get them to unblock ports for RAS to work properly and not drop ever 2 minutes - this was several years ago though), but I don’t think they do anymore.

  2. Comcast’s modems don’t have any settings pages that I’m aware of - at the very least I’ve never seen one, and never been directed to one by their support people. They have remote control over the modems so it seems unlikely there is one.

One thing you might find annoying - Comcast does DNS Hijacking. You can opt out at https://dns-opt-out.comcast.net/

7

You will have to provide better information - best with numbers - to get a useful reply. For example, list all the IP addresses from IPCONFIG.

Your protection on cable is equivalent to the protection you had via the DSL modem.

How to setup a router modem? Best start with information on current router configuration and other status page information.

Most cable modems do not provide the so much more useful information provided by DSL modems. For some reason, Comcast considers users do not need to know that stuff. Maybe that Cisco is newer; can provide that information. But traditionally, Comcast equipment provides as little information as possible. Useful would be, for example, is the Cisco configured as a bridge or as a router? As a router, its IP address typically would be 192.168.x.1. And your computers ethernet port would be 192.168.x.yyy.

But again, to get a definitive answer, then first provide numbers.

8

OK, here’s what comes up when I do an ipconfig /all in the command window:

IP address: 76.105.164.188
Subnet Mask: 255.255.252.0
Default Gateway: 76.105.164.1
DHCP Server: 68.87.69.13
DNS Servers: 68.87.69.150
68.87.85.102

The cable modem is a Cisco 2100 per the label. There are only the ports I described on it, namely, the Coax connector port, the Ethernet RJ-45 port, and the power connector.

So is the first one my public IP address?

Anyone know of some good speed tests BTW? I want to see what my new service can do.

9

I don’t have experience with that model. But these numbers say your Cisco is configured as a bridge. Your computer is connected directly to the internet. Directly to the Comcast computer at 76.105.164.1. IOW your Cisco would only have one ethernet port.

When moving a wireless router to it, I recommend holding down the reset button and powering it. The wireless router should connect direct to the internet.

Now Comcast is probably expecting to also see your computer’s MAC address. Maybe 0F-45-01-C4-22-04 . A random MAC (physical) address to demonstrate what to search for. Don’t remember. But maybe this command will give it:
IPCONFIG /ALL or
ARP /A

MAC address is assigned uniquely to every ethernet card, part, router, etc by the manufacgturer. Every ethernet interface has a uniqe MAC address.

To change (spoof) the routers MAC address, you will probably have to talk to its server at 192.168.1.1 from your computer - without any Comcast connection. Once setup, then connect the router to that Cisco.

Configure the router to ‘spoof’ your computer NIC’s MAC address. Comcast equipment at 76.105.164.1 wants to talk to that MAC address. Then their DHCP server leases an IP address to your router thinking it is your computer.

Your router looks to Comcast like the NIC (same MAC address) as in your computer.

When your router is reassigned (spoofs) the MAC address of your computer’s NIC, then Comcast simply assigned an IP address to what they think is your computer. Something like 76.105.164.zzz

Now, your router’s DHCP will assign your computer with a new IP address. From the computer, your router will be 192.168.x.1. And your computer will be 192.168.x.yyy.

On the other side of your router, Comcast automatically leased to your router an IP address of 76.105.164.zzz.

Finally, you can record the MAC address of the router with Comcast (rather than spoof the MAC address they already have). Call Comcast to change their records. To change the recorded MAC address from your computer NIC to your router’s default MAC address. Your choice. Mine is to avoid doing that during daylight hours when the technical people do not seem to have as much knowledge. Just my preference in avoiding the most difficult part in every solution - a tech support person.

Hopefully I have told you what do by also introducing what these MAC and IP addresses actually do.

10

http://www.speakeasy.net/speedtest/ has always worked for me

11

Comcast employee here. If you want your wireless router to act as a router, then from the wall go modem (your Cisco), then the wireless router. Factory defaults will likely work on the router. DHCP tends to be the default these days. You’ll need to reset the moddm afterwards.

As for the modems own configuration, it is hidden for a reason. There is nothing an end user needs to ever touch.

There is no need to spoof your mac address or anything like that.

12

So basically, as long as I set the router to DHCP as a connection type, and enable its DHCP server, I should be able to just hook it up? And then you say I’ll have to reboot the cable modem by pulling its power cord for 15 seconds or something?

13

Yes to all of the questions. So long as the router is set to DHCP it should be good.

14

That question is made irrelevant by doing the master reset described up top.

You can let the router access DHCP. Or setup each computer to do DHCP access. And irrelevant. Hold the routers reset button and power it on - as posted. Hold that button maybe up to ten seconds. Default is to get DHCP IP server addresses automatically from the Comcast computer at 76.105.164.1. And the router’s IP address (maybe 76.105.164.xx) is automatically leased.

Your only concern may be assignment of a MAC address - as described earlier. All that other stuff is automatic with a router reset.

Meanwhile, Comcast considers us too dumb to view Signal to Noise numbers. That critically important number is how to determine which side of the modem has a failure. DSL modem provide that so useful information that many times even eliminates calls to customer service. Comcast thinks we are too dumb to be trusted with useful facts.

BTW, it not just consumers. Many Comcast linemen have spent $5000 for better equipment to find failures most often identified by insufficient dB numbers. I was shocked how many linemen spend their own money for what provides useful numbers rather than use what Comcast provides.

15

Thanks for all the replies. I didn’t particularly want to reset the router to factory defaults (which would have involved resetting its security and making a bunch of changes to the security settings of my TiVo, consoles, etc.), so I just turned on its DHCP server, changed its IP address to 192.168.0.1. (because that’s the gateway those devices are looking for) and made sure the connection type was DHCP, then hooked everything up, rebooted the cable modem and everything is good now. Didn’t have to do MAC address spoofing or anything.

16

Good to know. I guess they stopped using MAC addresses to confirm you are an authorized customer. Makes sense. And another fact that the ‘powers that be’ would rather not have us know.

Did not realize you had all those other configuration changes. Consider recording those unique router configurations and passwords somewhere safe in case an unfortunate disaster happens. Best with a new router is to start with what is known in writing to have worked.

17

FWIW, I’ve been working for Comcast(and before that, AT&T Broadband, and CableVision before that) since high speed internet first launched in Boston, and we’ve never required a user to spoof a MAC address to get a router working.

18

It was done at one point in Seattle. I specifically had to spoof the MAC to get it working a few years ago.

19

I think generally ISPs won’t really require a specific MAC address to get it working, but they will limit the number of MAC addresses that they’ll give out DHCP leases to, to keep people from just grabbing a bunch of IP addresses. If you’re lucky the limit is at least 2, and you can swap a new device in without having to clone a MAC address, but at some places the limit is 1 and cloning is just a quick way to get around having to wait for the current lease to expire.

20

Demonstrated are many ‘ways of doing it’. An ISP will sometimes short all users of facts. Because to a consumer is best left uninformed. This is a two way street. The person who asks for help then provides useful information. And that good thing happened here.

Some ISPs did spoofing. Many of what are now Comcast regions did spoofing. But the OP now suggests spoofing is no longer required for Comcast. Good to know, in part, because Comcast has an intermittent habit of shorting facts. Especially in customer support. In some cases, to avoid fixing problems in their network. Some consumers might quickly identify their constant service problems if that modem provided signal strength numbers in dBs. Then take action based in facts.