General cable modem questions

[videobruce]

I have had DSL for years and never had any experiance with cable modems. I have a few generic questions about them. The one in use is the Motorola SB5100 on what was Aldelphia, now Time Warner cable. There is also a Linksys router in the mix.

1. Adding a broadband amp (US made Winegard 40-1000MHz) seems to kill the modem. Is it because of excessive signal or is there a need for coverage below 40 MHz? Mind you, this isn't one of those cheap no-name Chineese made wonders. It is only a 10db gain, so I doubt it is a excessive signal issue. I would say there is around +5-10 dbmV of signal with the amp.
2. I was told (by TW support) that you have to leave the configuration of your NICs' to "Obtain a IP address automatically". Is this true? I perfer to assign each conputer with a static IP address. With DSL, I have no issue here, so I don't understand why cable would be different. What does the output of the router have to do with what the modem sees??

Hope all of that makes sense.

[doctorgonzo]

1. Adding any kind of amp or booster to the cable your cable modem is on is a bad idea. Besides, there is never really a need for it.

2. Since you have a router, you can assign IP addresses. Just make sure that your router is set up to get the WAN IP address automatically from the cable modem, and that DHCP is turned off.

[videobruce]

Besides, there is never really a need for it. Low signal, because of splits ahead of the modem. and that DHCP is turned off. Doesn't cable require "automatic DHCP" just as DSL requires PPPoE?

[doctorgonzo]

If you have splits ahead of the modem, try rearranging the splits so that the modem gets a signal that is split once at most. It may be impossible to do this, but that's a much better option than a booster. Cable Broadband is two-way communication, and so it is a very different beast than simply boosting a TV signal.

When I said turn off DHCP, I meant turn it off at the router for the LAN side of the network. Your router will get an IP address from the cable modem for the WAN address, so don't enter a static WAN address in the router. On the LAN side, however, you can do whatever you want. You don't have to use DHCP on the LAN side if you want static addresses.

[videobruce]

If you have splits ahead of the modem, try rearranging the splits so that the modem gets a signal that is split once at most. That can be done. don't enter a static WAN address in the router Never did. I will scope out Linksys site for the manual for the router.

[doctorgonzo]

If everything is working (you can get to the net from your computers), then your WAN settings are fine. All you need to do in that case is go to the router's configuration page, and then turn off DHCP on the LAN side.

[videobruce]

turn off DHCP on the LAN side. Understood, if I can find that page. I have the manual and will look through it.

[glc]

You need a high bandwidth 2 tap splitter as the FIRST split after cable entry into the house. It must be at least 1 GHz, but higher is better. The cable modem must be connected directly to one tap, you can run the other tap to whatever you want.

[videobruce]

I understand the issue (had a idea it was this). The amp isn't bi-directional and it doesn't pass below 40 MHz.

Ok, past that, why is the router considered the "Gateway" why the modem is the first device?
Why is the computers NIC MAC address the one the CC is interested in when the modem (usually theirs) is what connects to the HE (see forst question)??

[glc]

The router is the gateway to your computers because it's the device assigning local IP addresses. There's 2 levels of MAC for security and identification purposes - what's to stop someone from stealing your modem and using your account?

[videobruce]

what's to stop someone from stealing your modem and using your account? Scarface is my next door neighbor. :eek: (I couldn't resist)

No different than a stolen CC. You report it stolen, the account is closed.

[glc]

That was just an example. It uses the MAC of the modem and the MAC of the first downstream device to irdentify your connection.

[videobruce]

To make a long story short, the 'threshold' of the modem seems to be around -5 to -8dbmV. This is where the handshake becomes iffy. When I returned to the scene the PC had internet access. It wasn't that way when I left and nothing was changed. No idea what happened.

[glc]

That says that the signal strength is marginal. This can be caused locally by more than one splitter between the modem and cable source or low grade cables or splitter - or a weak signal to begin with.