Worldpath DSL

Ben Scott dragonhawk at gmail.com
Sun Jan 1 18:31:01 EST 2006


n 1/1/06, Lawrence Tilly <mail.list.tilly at gmail.com> wrote:
> Just to clarify, I haven't ordered the static IPs yet.

  That will make things harder.  :)

  To address your current problem: I've not experience with your model of
DSL modem, but I've encountered similar trouble.  What usually happens is
that some kind of NAT is done on the "modem".  Your config ends up looking
like this:

ISP <--------[modem]--------------> LAN - 192.168.1.0/24
             |     |
  24.34.44.212     192.168.1.1

  In the above example, your "modem" has a DSL interface with IP address
24.34.44.212 [1].  The Ethernet interface of the modem has an address from
the RFC-1918 private address space.

  Does that describe your setup accurately?

  With the above, you can often configure the modem to forward services from
the public IP (24.34.44.212) to a host on the LAN.  The problem is that the
modem's admin UI is already bound to TCP/80, and it grabs that before any
port forwarding can.

  As you surmise, the fix is to unbind the admin UI from the DSL interface,
or change the port number.

> I will be doing so on Tuesday when they reopen for business. I'm actually
> not sure yet how this will even be configured physically since I haven't
> spoken to a rep.

  Typically, they give you a small routable IP block, and your config then
looks something like this:


ISP <--------[modem]--------------> LAN - 24.34.45.48/29
             |     |
  24.34.44.212     24.34.45.49

  In the above .  A small netblock, 24.34.45.48/29 [2], is delegated to your
site from your ISP.  The Ethernet interface on the modem uses .49 from that
block.  You're free to use .50 - .54 for your own equipment.  You likely end
up assigning the "Internet" or "WAN" interface on your LinkSys box one of
those addresses.

Footnotes
---------
[1] That's actually my current Comcast cable Internet IP address.  Please
    don't try using that.  :)
[2] I got that by adding one to the third octect of my IP.  Hope the real
    owner doesn't mind.  :)

-- Ben



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