At 02:15 29/11/01, Jeffrey Altman wrote:
I have Cable Modem service from Time Warner Road Runner in NYC.
The way they work it you get up to 5 IP addresses for each cable
modem you have.
This is typical of most {NB: not all, most} currently deployed
residential IP/Cable Modem networks in at least US and Canada.
The problem I have run into is that the modem gets
assigned the number of addresses you pay for up front.
The modem then assigns them, one to each MAC address it sees until the
number of addresses is used up. Now if you connect a switch to the
cable modem the LAN and WAN MAC addresses of the switch will be seen
by the modem and two of your IP addresses will become inaccessible.
As far as I can tell there is no way to specify to the modem which
MAC addresses should be issued IP addresses.
The DOCSIS standards used in many countries (including the EuroDOCSIS
variant with 8 MHz downstream channel width that is sometimes used
in Europe) do not permit the operator to configure the information
into the DOCSIS cable modem in the manner you would like, as near
as I can tell. So the cable network operator isn't being malicious,
just limited by the currently deployed technology.
This means that for the first three addresses you get one computer.
Four addresses for two computers, five addresses for three computers.
Understood, though a strictly-compliant Ethernet bridge device ought only
have a single MAC address (not 2 or more). While many low-cost devices
aren't strictly-compliant to the Ethernet standard, the Ethernet spec
does say one MAC per box (not one MAC per network interface). Sun,
for example, is strictly compliant with this part of the spec even
if their systems have multiple interfaces, so compliance with the
Ethernet spec isn't unheard of.
Ran
rja(_at_)inet(_dot_)org