[lug] Re: SurfBoard Cable Modem...

John Hernandez John.Hernandez at noaa.gov
Mon Aug 28 10:37:09 MDT 2000

I'm wasn't surprised to find that the User Guide for this device is
written for a non-technical audience.  Basically, it's useless.

Here's what I discovered (quite by accident).  If you generate a DHCP
query during the modem's initial power-up negotiations (while lights are
flashing), it should respond by assigning you a private IP address in
the neighborhood of  In this scenario, the modem's
10baseT port binds  I used 'nmap' to discover that the
modem listens on tcp ports 80 and "filtered" 513, corresponding to http
and login.  Hitting the modem's web server reveals some interesting
debugging and reporting capabilities, but not much else.  The login
service was non-responsive, but my probes were admittedly half-hearted.

To the best of my understanding (which may be completely off-base), once
the power-up sequence is sucessfully completed, the device switches to
layer-2 bridging mode.  It should be capable of learning more than one
MAC address on it's 10baseT port if you use a hub.  At this point,
however, DHCP queries will be handled by one of @HOME's servers, which
require you to provide an assigned "computer name" in exchange for your
address.  @HOME would most likely provide you with additional "computer
names" (and hence addresses) in exchange for your $$ :)  BUT, there must
(should?) be some mechanism to prevent you from just choosing an unused
address on their network.  IP doesn't like addressing conflicts.  Any
cable ISP techies out there??

If you already own a hub and run Linux, why not just use NAT?  Ipchains
is powerful and fairly easy to configure.  That would certainly be the
cheapest and least questionable (if not @HOME's favorite) approach.

My question to all is:  Anyone know anything about the SurfBoard cable =
modem?  Its manual says the modem can be used for up to 32 computers and
that "The network administrator at your service provider configures your
modem for multiple users."  Can I get in and change this stuff?

Can I telnet into it?  Anyone know any cool features it might have?

I found the product page at http://www.surfboard.com/, however I could =
not find anything of use over there.  I did not spend a lot of time, but
simply browsed around the site.


John Hernandez, Network Engineer --------------------------------------
US Department of Commerce                             tel: 303-497-6392
NOAA/OAR - Mailstop R/OM12                            fax: 303-497-6005
325 Broadway                            e-mail: John.Hernandez at noaa.gov
Boulder, CO 80303                               http://boulder.noaa.gov

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