networking question

Kevin J. Cummings cummings at kjchome.homeip.net
Thu May 28 20:52:15 UTC 2009


Gerhard Magnus wrote:
> One thing I've always liked about computers is that it's possible for
> one to do so much more than one understands; a little knowledge turns
> out to have a great deal of leverage. But now I'd like to backtrack a
> bit and learn something about the LAN I've already cobbled together.
> 
> My interface with the Internet is an Actiontec DSL modem (which I then
> have connected to a router.) When I use a browser to look at the modem's
> "status" window I see it's connected to a WAN (wide-area network?) which
> I assume is administered by my ISP. The WAN information includes an "IP
> address" and a "Gateway" which differ only in their last two sections
> (i.e. IP address xxx.xxx.181.193 and Gateway xxx.xxx.180.1) Why are
> these two addresses needed? (I'm thinking my LAN would only need one IP
> address.)
> 
> Thanks for the help on what's probably a very elementary question....

Yes, very elementary, the IP address is what you think it is, the IP for 
your DSL modem.  All of your incoming traffic is routed to/through it.
The GATEWAY address is for all of your *outgoing* traffic.  The DSL 
modem needs to know that it needs to be sent to that address in order 
for it to be delivered to the proper targets.  The GATEWAY is not a part 
of your setup, its another router in your ISP's network that you need to 
know about in order to use it properly.  Its the ISP's equivalent of 
your LAN's "default" route.  Your LAN sends outgoing traffic to gateway 
listed on your "default" route (which I imagine is your DSL modem) which 
then needs to send it to *it's* GATEWAY in order to get where its going.

Clear as mud?

-- 
Kevin J. Cummings
kjchome at rcn.com
cummings at kjchome.homeip.net
cummings at kjc386.framingham.ma.us
Registered Linux User #1232 (http://counter.li.org)




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