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.

[rendrag]

1. I'm not sure on that one... maybe one of the other members can help us out.

2. Behind a router, you can do whatever you want. If you want to statically assign the IPs, you can do that. What they're probably talking about is the router's WAN interface. Where you would set PPOE, or whatever protocol for DSL, one of your choices will be DHCP... that's generally what you set for cable modems. You'll also have to adjust the MAC address in the router to match the PC that initially configured the modem, as cable ties your account to a MAC address

[bledd]

2. you use their modem, straight into your router, you can tell your router to do whatever you want, i use a mixture of static and dhcp, no problems, have done for years with dsl and cable, they're probably telling you to use dhcp, so you don't ring them up if you can't get manually issigned ip's to work (if you don't know how to set it up!)

obviously just set your dns and gateways (on the clients) to 192.168.1.1 (if this is the default of your router)

[videobruce]

First question answered elsewhere. Amp has to be bi-directional and cover below 40 MHz, neither was covered with the amp I have. NO problem, I can work around it.

You'll also have to adjust the MAC address in the router to match the PC that initially configured the modem, as cable ties your account to a MAC address

I understrand this, but why and how can the CC HE (head end) know or care about the NIC MAC address? Why isn't the modems address enough? After all, it is the first link from the CC.

Related question; why is a router called a "Gateway" when in fact the 'modem' is the device that actually 'sees' the internet first (at the customers house)?

If there is no router, what is considered the "Gateway" then, the NIC?

[rendrag]

I understrand this, but why and how can the CC HE (head end) know or care about the NIC MAC address? Why isn't the modems address enough? After all, it is the first link from the CC.

I never understood why cable ISPs tied the MAC address of the first NIC to the account... that question would probably be best answered by the provider.

a router acts as a gateway to the internet. If there was was no router (i.e. you were directly connected to the modem), the router at the ISP would be your gateway.

[videobruce]

I never understood why cable ISPs tied the MAC address of the first NIC to the account.

Paranoia? More security for the CC? So one couldn't take their modem over somewhere else and use it there? Not much of a reason if you ask me if that's it.

If there was was no router (i.e. you were directly connected to the modem), the router at the ISP would be your gateway.

I read that, now I'm more confused. Then why isn't the ISPs' router still the "gateway" if you have a router?? Edited August 21, 2006 by videobruce

[rendrag]

So one couldn't take their modem over somewhere else and use it there?

It's not very secure because you could just take your modem and router (since you cloned the MAC address in order to get online) to someone else's home and use it.

I read that, now I'm more confused. blink.gif Then why isn't the ISPs' router still the "gateway" if you have a router??

Technically, the ISP's router is still the gateway, but when you use a router, your PC's gateway is the router, and the router's gateway is the ISP's router. Make sense? If not, hopefully this will explain it better:

A network gateway joins two networks together. A network gateway can be implemented completely in software, completely in hardware, or as a combination of the two. Since routers are generally used connect 2 seperate networks, for all intents and purposes, a router = gateway.

If you are connected to a router in your home (linksys, dlink, whomever), it will act as your gateway to the internet (which is just a collection of networks). Your router's gateway will be the router at your CC. This is the same gateway if you were connected directly to the modem, bypassing the router.

[videobruce]

It seems as the term "Gateway" is very broad and this is where the confusion is coming from. It can be used in various ways.

(Almost 60 views and no one else has anything to add??)

Edited August 21, 2006 by videobruce

[RogueSpear]

The term "gateway" as I have always understood it, means the address that traffic is sent to when it is determined that the traffic is not going to another host on the local network. You need three basic things for IP connectivity - an IP address, a subnet mask, and a default gateway. That's the in-a-nutshell explanation of it. Anything that would be much more in depth than that could easily take up pages and get complex rather quickly.

If you truly have an interest in the fundamentals of IP then I would suggest checking out the following site:

http://www.learntosubnet.com

With Adelphia, and I would assume it will be the same with Time Warner, you must have your Internet facing interface set to use DHCP. Static IP addresses are not available for home accounts, though they may be for commercial accounts. Your router will have two primary "interfaces", not to be confused with the one or more RJ-45 ports for clients to connect into. One interface is the Internet facing interface and this will be set to a legal IP address. The inside interface will likely be set to the default of 192.168.1.1 as most manufacturers use this. The 192.168.x.x range is known as private. It is not routeable through the Internet. The 192.168.1.1 is going to be the "default gateway" for your computers that are connected to the router. Network Address Translation (NAT) is what allows you to have multiple computers sharing the one single IP address assigned to your router's Internet facing interface.

If you were able to make sense of all that, or even care for that matter, and still have more questions, I'd be happy to try and answer them.

[videobruce]

If you were able to make sense of all that, or even care for that matter

Yes to both.

you must have your Internet facing interface set to use DHCP

Yes, already set that way by default.

Static IP addresses are not available for home accounts, though they may be for commercial accounts.

Yes I know.

The 192.168.x.x range is known as private. It is not routeable through the Internet. The 192.168.1.1 is going to be the "default gateway" for your computers that are connected to the router.

Already understood.

Network Address Translation (NAT) is what allows you to have multiple computers sharing the one single IP address assigned to your router's Internet facing interface.

Pretty much understood.

Unfortunately I don't have the router here or have screen shots of some of the interface pages, or it would be easier. I have looked over the manual and think I know what/where the pronlem is, but untill I actually go back, this is kinda in limbo.

I'm just more use to DSL I guess.

[Pete_]

Im using cable modem+ NAT router too, working fine! Router has also wlan, so using laptop is no problem