Ask Me Help Desk - CABLE and Modem Router

Hi

my buddys has a cable modem which she connects to the internet with, its got one USB and one ethernet port on the modem.

Ive only seen t he modem through webcam so I couldn't play around, we were NOT able to connect 2 machines one through usb and the other through ethernet.

The cable modem allows a router to be connected.

I have a BT VOYAGER 2100. I would like to connect that into the ethernet port of the cable modem.

Im trying this at home but I've not been able to connect to the internet. I have 2 voyager 2100 so when I connect from the seconds modem it gives me the ip of the first modem sometimes and sometimes the second modem.

Help!

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Hi

Cajalat: Thanks, that clears up so much regarding the cable modem (usb and ethernet cannot be used simultaneously)

My hopes: on my second voyager 2100 I have disabled dhcp and get a great internet connection now (2 voyagers).

Will this work... My friends house who is connected via cable internet. If I plug my voyager into her ethernet port of the cable modem. Will I then be able to use the 4 ethernet ports to access the internet (dhcp is disabled in voyager).

The manual on the cable modem says it can take up to 64 ethernet connection, who will act as the router my voyager or her cable modem?

Thanks

You connect the cable modem to the WAN port of the router via Ethernet. You then connect your PCs to the router either via a wired or wireless connection. The DHCP server built into the router should handle assigning of IP addresses to the PCs.

You have two separate problems here. The first one deals with connecting your BT VOYAGER 2100 to your friend's Cable modem. The 2nd deals with you trying to connect 2 BT VOYAGER 2100 together.

For the first problem the answer is likely you can't. Most cable modems do have a USB, an Ethernet, and Coax. The Coax connects to your cable TV line. The USB OR the Ethernet are used to connect to your PC (or router). You can't use both at the same time. It is one or the other.

For the 2nd problem is that you're trying to connect 2 ethernets together which are competing with each other. You've connected the 2 BT VOYAGER 2100's via their Ethernet's which each BT VOYAGER 2100 will have its own DHCP server (as scott mentioned). You must disable the DHCP server on the BT VOYAGER 2100 that is connected behind the BT VOYAGER 2100 that has the DSL connection. In other words, keep the DHCP server enabled on the BT VOYAGER 2100 that is connected to your ADSL line and disable DHCP on the other.

Hi

Cajalat: Thanks, that clears up so much regarding the cable modem (usb and ethernet cannot be used simultaneously)

My hopes: on my second voyager 2100 I have disabled dhcp and get a great internet connection now (2 voyagers).

Will this work... My friends house who is connected via cable internet. If I plug my voyager into her ethernet port of the cable modem. Will I then be able to use the 4 ethernet ports to access the internet (dhcp is disabled in voyager).

The manual on the cable modem says it can take up to 64 ethernet connection, who will act as the router my voyager or her cable modem?

Thanks

The cable modem is not a router. That's why you need a router. The purpose of the router is to manage multiple PCs in a LAN as they share a single Internet connection (the modem). Your rotuer (if I have the modem correct) supports both wired and wireless connections. When you connect the router to the modem, you are essentially creatiing a LAN. Any devices you connect to the router will be on the LAN and can share the Internet connection or their own resources.

hmm.. I know its not a router!

when I tried voyager1 to voyager2.. the ip (pc1) showed the ip and default gateway of the voyager1 which is connected to the adsl. However the pc1 is connected to voyager2 (voyager2 is connected to 3 machines and 1 port connected to voyager1) who will assign the dhcp when voyager2 dhcp is disabled.

will it work.. My friends house who is connected via cable internet. If I plug my voyager into her ethernet port of the cable modem (usb port empty). Will I then be able to use the 4 ethernet ports to access the internet (dhcp is disabled in voyager).

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Motorola SURFboard SB5100

• Supports up to 32 users (1 via USB and up to 31 via
Ethernet or 32 users on Ethernet)
• Ethernet and USB connections are bridged allowing LAN
traffic between USB device and Ethernet LAN (failed to run both simultaneously)

I'm not following what you are trying here. Why are you using 2 routers in the first place?

If you plug a broadband router into a broadband modem (cable modem to the voyager) then you can use the ports on the router to access the Internet. If you plug a second router into the first router and disable DHCP, you can then use the ports on the second router to share the Internet. In the latter case, you are just using the switch part of the router.

I'm going to ditch the voyager 1.. And use only cable modem and voyager 2 (my friend only has cable broadband)

Quote:

Originally Posted by funk999

Hi

Cajalat: Thanks, that clears up soo much regarding the cable modem (usb and ethernet cannot be used simultaneously)

My hopes: on my second voyager 2100 i have disabled dhcp and get a great internet connection now (2 voyagers).

Glad you're set on the above.

Quote:

Originally Posted by funk999

Will this work... My friends house who is connected via cable internet. If i plug my voyager into her ethernet port of the cable modem. will i then be able to use the 4 ethernet ports to access the internet (dhcp is disabled in voyager).

The short answer is no. This will not work. As ScottGem mentioned the cable modem is not a router and it doesn't issue DHCP addresses. CableModems are designed to have either a router or a PC plugged into it. If you plug a PC then you get a DHCP address from your ISP. If you plug a Router then your Router gets a single IP and any PC behind the router is NAT'ed. Some Cablemodem ISP's even lock the IP to specific MAC address so that you only get an IP address for a specific machine.

Now when you plug your Voyager's Ethernet connection to the CableModem's Ethernet connection and a PC into the Voyager (DHCP disabled) then what is likely to happen is that you'll get an IP address from your ISP via the CableModem and that IP is assigned to the first device that requests it (i.e. the first PC you plug in). The 2nd PC you plug into the Voyager will not receive a DHCP address because your cablemodem is usually only programmed to provide 1 IP address. If you enable DHCP on your voyager then you in essence break the rules of your ISP by having a DHCP server facing the ISP (big no no) and might risk getting blocked.

Your problem is not that you can't plug a router into the cablemodem. Your problem is that your Voyager is a DSL router and not a Cablemodem Router. The Internet facing connection on your DSL router is an RJ11 which plugs into the phone line. A cablemodem router has a port called WAN port which would plug into the Ethernet of the Cablemodem. You simply have the wrong kind of router for cable internet.

Quote:

Originally Posted by funk999

The manual on the cable modem says it can take upto 64 ethernet connection, who will act as the router my voyager or her cable modem?

Thanks

True... the cablemodem can handle that many connections. However, your ISP is in control of the configuration of the cablemodem and it is up to the ISP to allow that many unique devices. You can ask the ISP if they allow multiple PC's directly through the cablemodem (i.e. if you plug a hub or a switch into the cablemodem). If the answer is yes then you can plug your Voyager's ethernet into the cablemodem's ethernet and you'll be able to access the internet from as many PC's as your ISP allows. The Voyager is only acting as a plain switch at this point.

Hope that helps.

Quote:

Originally Posted by cajalat

Glad you're set on the above.

True...the cablemodem can handle that many connections. However, your ISP is in control of the configuration of the cablemodem and it is up to the ISP to allow that many unique devices. You can ask the ISP if they allow multiple PC's directly through the cablemodem (i.e. if you plug a hub or a switch into the cablemodem). If the answer is yes then you can plug your Voyager's ethernet into the cablemodem's ethernet and you'll be able to access the internet from as many PC's as your ISP allows. The Voyager is only acting as a plain switch at this point.

Hope that helps.
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That's so helpful, I'm sure I could figure this out if I had this scenarios physically in front of me.

The isp does allow virgin.net to connect more than one PC, so I need the voyager to act as a switch or hub. So I gather I will need to turn on DHCP on the voyager, so wouldn't the voyager and cable modem fight to assign ip? I think you are saying the ISP DHCP will give us the ips? So voyagers DHCP should be off.

Or.. how should I do it?

Are you sure the ISP provides multiple IPs or that they just let you use a router. If you use a router, the cable modem will see it as a single device and will not assign multiple IPs. It will let the DHCP server on the router handle that.

Quote:

Originally Posted by funk999

Thats soo helpful, im sure i could figure this out if i had this scenarios physically in front of me.

The isp does allow virgin.net to connect more than one pc, so i need the voyager to act as a switch or hub. So i gather i will need to turn on DHCP on the voyager, so wouldnt the voyager and cable modem fight to assign ip? I think you are saying the ISP DHCP will give us the ips? so voyagers DHCP shud be off.

or.. how should i do it?

Yes I'm saying that you should turn off DHCP on your Voyager if you plan to connect them together on the LAN side because your ISP will assign the IP's instead of your Voyager.