The tech showed up, changed all the cable connectors and the cable modem, said it appeared to be working fine and I should call if I continue to have problems, and left.
He also said that he has been repeatedly told that a customer should only use one of the two ethernet ports on the cable modem. He further said that he has asked why not and why does the cable modem have two ethernet ports if a customer should use a maximum of one, and he has never received a satisfactory answer.
He also said that he has no idea how a customer would connect to a web interface to the cable modem and that the customer should probably not be changing anything anyway.
It’s because each customer gets only one IP address. That’s typical for home consumers. Presumably there are business/commercial customers who get two IP addresses for their service and they would be able to use two ports.
I’ve never had a cable modem with more than one ethernet port myself.
I don’t see how ports and addresses are related. The customer gets one IP address which goes to the switch in the cable modem. That switch then does NAT to whoever is on its LAN or wifi. In that sense it’s irrelevant if you connect two clients to those two Ethernet jacks directly or if you connect a dumb hub to one of those jacks and then connect your two clients to that hub. Unless of course the modem somehow hardwires those two jacks to two separate switches which I highly doubt since this is a cheap modem intended primarily for residential consumers.
Some cable modems are combination modems and routers, and those are generally the ones that will also provide WiFi and should have multiple switched ethernet ports, as you describe. But a traditional cable modem is just a bridge rather than a switch that converts the signal from the cable provider (over coax or fibre usually) to ethernet internally and is not a router.
In Will’s case, if you do have a router/modem combo, you will still want to connect only a single ethernet port if you are using an AirPort as a router and not a bridge, or the devices that are connected to a second (or third or fourth) ethernet port will not see the devices connected to the AirPort network, because they are protected by the firewall on the AirPort NAT router. The ethernet ports on the cable modem/router are a completely different network from the devices connected to the AirPort router (though the devices not he AirPort router can see those other devices because they can connect to things upstream.) Having a router connected to a ISP-provided router leads to something called double-NAT when you do it, which is usually not much of a problem for most people, though I think that gaming consoles can have trouble, and anything providing services with UPnP might have trouble. Putting the AirPorts in bridge mode would solve any double-NAT problem and would allow you to use multiple ethernet ports on a modem/router combination.
And, of course, I jinxed it. Same as before. (But I had said it was intermittent.)
FWIW, the tech specifically suggested the dumb hub as an alternative if I wanted two ethernet connections.
The AirPort is connected as a router (it assigns IP addresses), but it had been the only device connected to the cable modem for a long time when the problem started. It was only since then, while trying test the ISP’s allegation that Wi-Fi was the problem, that I connected to the second ethernet port. As far as I can recall, even when two devices were connected to the cable modem, there was traffic on only one device at a time.
I have told the ISP that the AirPort is a router and received no criticism. No one here does gaming, there is no gaming console, and the only problems I’ve had with my extremely limited use of Plug and Play could be attributed to my ignorance more than networking.
He’s right. As @ddmiller pointed out, if you have several LAN clients you likely want them on the same network and the way to achieve that is by putting a switch (even most “hubs” nowadays are technically switches w/o UI) directly downstream of the cable modem. For most people an AirPort Extreme serves exactly that purpose. But I question that using both those ports at all must result in mayhem, and if it does I would question the weird cable modem logic that leads to the issue. As I said above, ports and public IP addresses are two entirely different matters.
As others have pointed out, it may be a combo modem/router device. This is typically what ISPs lease so you don’t need additional equipment.
When running in router mode, there will (typically) be NAT operating on the router, so you can use both ports without problem. When it is configured to be a modem-only device (that is “bridge” mode) then both ports go straight to the Internet (via the ISP). But if you don’t have a business account, you will only have one IP address, so only one connected device will operate properly - the other will either not have an address, or it will have an incorrect address, or it will share the address with another device - all of which are bad.
If the modem’s router functionality is disabled, then you only want to use one LAN port to connect it to the WAN port of a router (like your AirPort), and let all your devices access the Internet via the router’s Wi-Fi and Ethernet interfaces.
Sounds like he didn’t look all that closely. You should be able to get something like an owner’s manual from your ISP’s support web page or from the modem’s manufacturer.
Point a web browser at the modem’s IP address. For example, if it is 192.168.10.1, then type http://192.168.10.1/ in a web browser’s location bar. Mind you, it might be a bit tricky to get its address if its router features are turned off. In my case, what I did was:
Disconnect my router from the modem and connect a computer directly to it, so nothing else will interfere with the next steps.
Factory-reset the modem’s settings. This set it back to modem+router mode, reset the password to the factory default and gave it a default IP address (192.168.0.1, if I remember correctly). If you have the manual for the modem, it will say what these factory defaults are.
Connect to the modem’s web interface and set it back to bridge (modem-only) mode. Let it restart.
Go back to the modem’s web interface (192.168.0.1 remains valid) and use that interface to change the modem’s IP address. I changed it to 192.168.100.1, in order to avoid possibly conflicting with my LAN addresses (which are all in the 192.168.1.* block).
Disconnect the computer from the modem and re-connect the router to it.
Now, if I point a web browser at the modem’s address (e.g. 192.168.100.1), I get its configuration screen. If I point a web browser at the router’s IP address (e.g. 192.168.1.1), I get the router’s configuration screen.
Definitely true. For several years, I worked at a remote office which used a business cable connection for its Internet connectivity. We paid for a “/28” network, where the last three bits of the IP address (e.g. from 10.0.0.0 through 10.0.0.7) were assigned to us. Three were reserved - the all-ones address (e.g. 10.0.0.7) is the subnet-broadcast address, the all-zeros address (e.g. 10.0.0.0) is the null-address, and one (e.g. 10.0.0.1) is the router’s address. The remaining 5 addresses were for us to use. We set up one to be used by a NAT router and reserved the other 4 for devices that needed to be accessed from the Internet.
And I agree with you about the number of ports. Typically, a modem-only device will only have one port, while a modem+router device may have more (typically 4 or 8, but I suppose some vendors may have 2).
In the case of that employer, the modem was located in the building’s telco room and we never saw it. There was a single Ethernet wire run from that room to our office. We connected a 5-port Ethernet switch to it and ran cables from that to our router and our non-NATed devices.