where is the DHCP server?

where is the DHCP server?
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Subject Author Date
where is the DHCP server? Phil Dartol 12-10-2005
Posted by Phil Dartol on December 10, 2005, 4:49 pm
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Hi,

I have some very basic questions about how DHCP works with a cable modem and
I couldn't find any answer in Google; and as I don't have a cable modem
(yet) I cannot test:

What gives the IP address to the computer: is it the cable modem, or the
server at the ISP side? Is it a "private" address (192.168.**) or a
routable address?

Second question: in the users manual of some cable modem (Terayon) I read
that the modem can serve more than one computer. Same question: does the
modem then works as a DHCP server (with 192.168.* addresses), or are these
IP addresses given by the ISP (in which case the cable transfers the
traffic of more than one IP address).

Thank you.

Posted by $Bill on December 10, 2005, 5:49 pm
Phil Dartol wrote:

> Hi,
>
> I have some very basic questions about how DHCP works with a cable modem and
> I couldn't find any answer in Google; and as I don't have a cable modem
> (yet) I cannot test:
>
> What gives the IP address to the computer: is it the cable modem, or the
> server at the ISP side? Is it a "private" address (192.168.**) or a
> routable address?
>
> Second question: in the users manual of some cable modem (Terayon) I read
> that the modem can serve more than one computer. Same question: does the
> modem then works as a DHCP server (with 192.168.* addresses), or are these
> IP addresses given by the ISP (in which case the cable transfers the
> traffic of more than one IP address).
>
> Thank you.

Your best bet is to go to your nearest electronics store Sunday that has
a sale on a Netgear or Linksys router and buy one (should be $30 or less).

If you think you'll ever need wireless than get a wireless G router with
4-port switch. The router will not only handle all your local DHCP needs,
but also keep your computers safe from Internet attacks - and they're cheap.

Here's the password to access your status pages on a TJ715 (not sure what
actual model you will have): icu4at!

Here are the pages you can access on a TJ715:

Main                http://192.168.100.1/mainPage
Troubleshoot        http://192.168.100.1/modemTroubleshootPage
Connection        http://192.168.100.1/modemRfPage
Advanced Links
Event Log        http://192.168.100.1/modemLogPage
Status                http://192.168.100.1/modemStatusPage
DS Freq                http://192.168.100.1/modemDsFreqPage
Configuration        http://192.168.100.1/modemConfigPage
Logout                http://192.168.100.1/logout


Posted by Bit Twister on December 10, 2005, 6:29 pm
On Sat, 10 Dec 2005 22:49:59 +0100, Phil Dartol wrote:
> Hi,
>
> I have some very basic questions about how DHCP works with a cable modem and
> I couldn't find any answer in Google; and as I don't have a cable modem
> (yet) I cannot test:
>
> What gives the IP address to the computer: is it the cable modem, or the
> server at the ISP side?

dhcp serer.

> Is it a "private" address (192.168.**) or a routable address?

routable. ISP DHCP server hands out ip address. Cable modem gets it's
address and your computer gets it's address.


Here a lease packet on my linux box.

lease {
interface "eth1";
fixed-address 24.1.202.185; <==== my routable ip
option subnet-mask 255.255.254.0;
option time-offset -21600;
option routers 24.1.202.1;
option dhcp-lease-time 345600;
option dhcp-message-type 5;
option domain-name-servers 68.78.85.98,68.78.69.146;
option dhcp-server-identifier 86.87.66.18;
option broadcast-address 255.255.255.255;
option domain-name "hsd1.tx.comcast.net.";
renew 0 2005/12/11 22:22:24;
rebind 2 2005/12/13 17:58:38;
expire 3 2005/12/14 05:58:38;
}

My modem ip address is 10.180.215.11 and my otorola SURFboard sb5120
has it's internal status web page at http://192.168.100.1


> Second question: in the users manual of some cable modem (Terayon) I read
> that the modem can serve more than one computer.

Yes, when off line. When on line, your computers get address from your
ISP where you may have to pay for the extra IPs.


> Same question: does the
> modem then works as a DHCP server (with 192.168.* addresses),

when off line.

> or are these IP addresses given by the ISP (in which case the cable
> transfers the traffic of more than one IP address).

Yes. Get a router, plug it into your cable modem and your computers can share
one ip address from your ISP.


Posted by James Knott on December 10, 2005, 6:58 pm
Phil Dartol wrote:

> Hi,
>
> I have some very basic questions about how DHCP works with a cable modem
> and I couldn't find any answer in Google; and as I don't have a cable
> modem (yet) I cannot test:
>
> What gives the IP address to the computer: is it the cable modem, or the
> server at the ISP side? Is it a "private" address (192.168.**) or a
> routable address?
>
> Second question: in the users manual of some cable modem (Terayon) I read
> that the modem can serve more than one computer. Same question: does the
> modem then works as a DHCP server (with 192.168.* addresses), or are these
> IP addresses given by the ISP (in which case the cable transfers the
> traffic of more than one IP address).

The DHCP server is at the ISP. Also, if your modem is like mine, it
provides a DHCP server, only when disconnected from the ISP.


Posted by Spam Catcher on December 10, 2005, 10:03 pm
ig@rogers.com:

> it
> provides a DHCP server, only when disconnected from the ISP.

Or for your internal private network ... some cable modems have a router
built in too.

--
Stan Kee (spamhoneypot@rogers.com)

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other useful resources:
The Federal Communications Commission (FCC)
Telecommunications Industry Association
Electronic and Software Security Products and Services
International Telecommunication Union

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