Subject: Re: trying to reconcile two threads

From: Jeffrey Altman <[email-masked]>
Date: Thu, 29 Nov 2001 2:15:35 EST

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.  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.  

This means that for the first three addresses you get one computer.
Four addresses for two computers, five addresses for three computers.

Now if you use a NAT device the WAN MAC address is seen first and gets
an IP address and then everything else gets private addressing.
Even if you want to play by the book, DOCSIS modems make things very
difficult.

- Jeff

Any ideas?

> I wish it were per-residence pricing. Here, if you want a 2nd (3rd, 4th,
> ...) IP address, the cable ISP expects you to connect a 2nd (3rd, 4th,
> ...) cable modem to the cable line. And they then charge additional fees
> for each such additional connection.
> 
> 	Tony Hansen
> 	[email-masked]
> 
> Keith Moore wrote:
> > 
> > > IP Addresses cannot at once be scarce enough to charge for and
> > > non-scarce enough that scarcity is a non-issue.
> > 
> > IPv4 scarcity is an issue, at least for customers.  Whether it's
> > an issue for large ISPs is a different question.
> > 
> > The cable ISP isn't really charging per-IP addresses; rather it's
> > charging per-residence.  The motiviation is not the scarcity of IP
> > addresses, but the scarcity of available dollars per customer -
> > in other words, they have an assumption that the amount of income they
> > can get from residental Internet service is more-or-less a constant
> > times the number of residental customers served.
> > 
> > So they use flat-rate, per-residence pricing to attract the largest
> > number of residential customers.  But they get annoyed when the
> > service is shared over multiple residences.  They'd get just as
> > annoyed if the mechanism were IPv6 instead of NAT.
> > 
> > Keith
> 

 Jeffrey Altman * Sr.Software Designer      C-Kermit 8.0 Beta available
 The Kermit Project @ Columbia University   includes Secure Telnet and FTP
 http://www.kermit-project.org/             using Kerberos, SRP, and 
 [email-masked]          OpenSSL.  SSH soon to follow.

---

From: RJ Atkinson <[email-masked]>
Date: Thu, 29 Nov 2001 10:03:12 -0500

At 02:15 29/11/01, Jeffrey Altman wrote:
>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

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.

>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
[email-masked]