Greetings,

Ok! Where did I get the impression that the SB6121 modem had a built-in router? It stands to reason that if it had, there would be more than one LAN port on the back of it. DUH! :|

Keep on BOINCing...! :)

Not necessarily. A single ethernet port (or, indeed, cable) can carry data for multiple logical devices on different IP addresses.

What is commonly called a "four port router" comprises (at least three) logical components:

1) A modem (modulator-demodulator) to convert the electrical signals (voltages, frequencies) between ethernet and DSL/DOCSIS.
2) A router to handle the translation between the internal and external interfaces, and ensure that the packets get forwarded to the right side.
3) A switch - effectively a port expander - to enable multiple devices to connect to the router conveniently.

You got the impression that the SB6121 modem has a built-in router because it does. It simply omits the switch (to save money), so you can spend your own money to buy an external port expander - if you had 8 or 32 devices, you would need to do that anyway, so you may as well not bother with the first four.

Greetings,

Ok! Where did I get the impression that the SB6121 modem had a built-in router? It stands to reason that if it had, there would be more than one LAN port on the back of it. DUH! :|

Keep on BOINCing...! :)

Not necessarily. A single ethernet port (or, indeed, cable) can carry data for multiple logical devices on different IP addresses.

What is commonly called a "four port router" comprises (at least three) logical components:

1) A modem (modulator-demodulator) to convert the electrical signals (voltages, frequencies) between ethernet and DSL/DOCSIS.
2) A router to handle the translation between the internal and external interfaces, and ensure that the packets get forwarded to the right side.
3) A switch - effectively a port expander - to enable multiple devices to connect to the router conveniently.

You got the impression that the SB6121 modem has a built-in router because it does. It simply omits the switch (to save money), so you can spend your own money to buy an external port expander - if you had 8 or 32 devices, you would need to do that anyway, so you may as well not bother with the first four.

Greetings Richard,

At this stage of the game, this is all a moot point. I needed a wireless router (access point) because we have 4 WiFi devices. But, through all my Internet searching and whatnot, I found what gave me the impression that the SB6121 had a 'built-in router'. This is from the Configuration page of the modem http access (or whatever it is called):

The SURFboard cable modem can be used as a gateway to the Internet by a maximum of 32 users on a Local Area Network (LAN). When the Cable Modem is disconnected from the Internet, users on the LAN can be dynamically assigned IP Addresses by the Cable Modem DHCP Server. These addresses are assigned from an address pool which begins with 192.168.100.11 and ends with 192.168.100.42. Statically assigned IP addresses for other devices on the LAN should be chosen from outside of this range.

Ok, so earlier in this thread, a couple days ago, I had a question and I do not see an answer. Because my memory ain't what it used to be, I'll have to search for the question and edit this post to re-ask it.

Be back in a bit... ;)

Keep on BOINCing...! :)
[edit] My question was why my modem shows a different MAC address, for the router, than what is printed on the router and router's box? The last number does not match. [/edit]

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CAPT Siran d'Vel'nahr - L L & P _\\//
Winders 11 OS? "What a piece of junk!" - L. Skywalker
"Logic is the cement of our civilization with which we ascend from chaos using reason as our guide." - T'Plana-hath

[edit] My question was why my modem shows a different MAC address, for the router, than what is printed on the router and router's box? The last number does not match. [/edit]

I have limited experience of working with DOCSIS or similar technologies, but I have some limited (and old) experience of connecting computers to the internet over the early iterations of Cable TV in the UK - I think it was known as TeleWest, or perhaps BlueYonder, at the time. Those were city-scale competing providers, all now subsumed into Virgin Media in the UK. The same principles will still apply.

Strictly speaking, the MAC address belongs to the network interface, rather than to the whole box. In Windows, you can see the MAC addresses for all interfaces by running

ipconfig /all

The laptop in front of me, for example, has a cabled ethernet interface with a physical address (MAC) starting "F0-4D-..." and a WiFi adapter with a physical address starting "8C-A9-...". Those are probably burned into the firmware during manufacture.

The early cable TV suppliers I mentioned were anxious that their revenues were not diluted by a single subscriber hooking up a shared connection for the whole street. So they licensed the subscription for one device only, and required pre-registration of the MAC address of the subscriber's (presumed one-and-only) computer network port. This worked, because the cable companies supplied true dumb modems which didn't have a MAC address of their own, but faithfully passed on the MAC of the computer plugged in to the other side of the modem.

Then router manufacturers joined in the arms race. A router will probably have two separate MAC addresses, one for the public interface pointing outwards towards the cable TV company, and one for the private interface pointing inwards towards your computer. If you simply plug one of those between your computer and the TV cable, the cable company will 'see' the public MAC address of the router, and that will be different from the pre-registered MAC address of the computer they're expecting. Result: breach of contract, and denial of service, until you ring up and re-negotiate the new MAC.

So the router manufacturers introduced 'spoofing'. Although their routers still had a public MAC address for the outward port, it was stored in flash memory and was editable. Some even supplied a button to read the MAC address of the computer being used to configure, and store it automatically as the router's outbound MAC address. So, the router's MAC address became that of the previous directly-connected computer (instead of the one printed on the box), and the cable company couldn't tell the difference. Instant connection, and no phone call.

I think the cable companies have largely given up fighting the spoofing war. I think Virgin now say (or did, the last time I worked on one of their systems) "switch off all your equipment, and wait a couple of minutes before switching it back on again. We'll accept whatever MAC address we find on the other end of the line after that". So, you can upgrade the subscriber equipment at any time, without the cable company needing to pay for a call centre to handle the re-registrations. Other companies may vary, of course.

It's possible that some modem/router devices supplied pre-configured for use with a particular provider's service may have some sort of automatic MAC spoofing pre-programmed to run the first time they're switched on. The difference you've spotted might result from that.

Greetings,

My apologies for resurrecting this old thread, but I thought it better than starting a new one. I will have the powers-that-be prevent further replies. :)

I just found out that this problem was also taking place on my Tablet. I was just on the BETA sight and found the MD5 errors there also. The new router seems to have fixed the problem. No errors since November... Woohoo! :)

Keep on BOINCing...! :)

---

CAPT Siran d'Vel'nahr - L L & P _\\//
Winders 11 OS? "What a piece of junk!" - L. Skywalker
"Logic is the cement of our civilization with which we ascend from chaos using reason as our guide." - T'Plana-hath