DNS Issues

[chuckx]

On Wed, Jun 05, 2002 at 08:16:25PM -0500, Jerry Place wrote:
>    I use port forwarding to differentiate the two Linux systems when 
> I SSH into them from my office.  This allows me to keep two full data 
> mirrors plus I have easy access to the two remote systems.  Port 
> forwarding also allows me to set up a secondary HTTP server from home 
> as a backup to my office server.
> 
>    Incidentally, RR will not give me another IP address.  

If you call in to the local office, getting additional dynamic IPs
provisioned for your account is trivial.  There is no additional charge for
them at the moment, all you have to do is ask.

> I suspect 
> they are using port monitoring to identify my first 48 bit NIC 
> address and when they see packets with another NIC address, they 
> refuse the DHCP request and I can't direct connect another system to 
> my cable modem, thus I use NAT through the router to keep both my 
> systems up and on line.  Pretty slick and easy to administer.

What you described is just about right.  Once you reach the maximum number
of clients your modem is configured for, network traffic from additional
hosts is not passed on to the cable network by the cable modem.  Notice that
your connection is not being actively monitored though.  Your cable modem is
a just network bridge that is configured to pass network traffic for a
limited number of hosts.  The modem does keep track of the hosts connected
to it via their MAC addresses.

Regarding IP addresses, the DHCP client ID sent by your system to the DHCP
server is the main factor in the assignment of your IP address.  If you were
to change you client ID your coputer (or router) is sending to the server,
you would be assigned a new IP address.

In Windows, the client ID is generated using the MAC address of the network
interface being used.  Unfortunately, you can't manually change that
behavior.

In Linux, using various DHCP clients, that behavior can be mimicked or
changed.  Therefore, in Linux, it's rather simple to get a new IP address. 
Consult the documentation for your DHCP client and send the server a new
client ID.  For example, for some reason or another, my Linux box was all of
sudden bombarded with what seemed to a denial of service attack from
multiple random hosts.  I wanted a new IP, so I ran this command -

dhcpcd -I "newIP"

and I was immeditately assigned a new IP.  The -I flag allows you to send
any client ID you'd like.

When it comes to home routers, as produced by Linksys, Netgear, etc., most
of them have an option to do MAC address spoofing.  My guess is that this
would influence the client ID the router sends in it's DHCP lease request. 
I can't say for sure, since I've never gotten around to messing with one of
them.

-- 
- chuckx | Charles K. Lee II -
- chuckx at cold-sun.com -
- http://www.cold-sun.com -
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