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.

Phil Dartol wrote:

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

On Sat, 10 Dec 2005 22:49:59 +0100, Phil Dartol wrote:
dhcp serer.

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


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


when off line.

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

Phil Dartol wrote:

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.

Thank you B, BT and JK, it's clear now.

Phil Dartol <no@mail.com> wrote:
A server on the ISP side (unless the cable modem isn't attached to a
live cable system, in which case the modem will assign a temporary IP
address).

That depends on your cable company. Most use routable addresses, but
some use private addresses and NAT.

As above, the IP addresses are assigned by the ISP. Some ISPs won't
assign more than one IP addresses per cable modem unless you pay an
additional fee. Many allow two or three. There used to be a few that
allowed four, but I don't know if they still do or not. I've never
heard of anyone allowing more than four without additional fees.

-Larry Jones

I don't need to do a better job. I need better P.R. on the job I DO.
-- Calvin

lawrence.jones@ugs.com wrote:

All IPs are routable. Some are supposed to be blocked from the internet.

James Knott <james.knott@rogers.com> wrote:
Indeed. I was using the OP's terminology but I should have said
something like "publicly routable", instead.

-Larry Jones

I hate it when they look at me that way. -- Calvin