Home Network Setup Problem
Greg Barniskis
nalists at scls.lib.wi.us
Fri Sep 9 12:18:10 PDT 2005
deltaski at earthlink.net wrote:
>>Is it a switch, is it a router, or is it really both (high end
>>thingy like Cisco 35xx?). Probably it is just a plain old switch
>>with no routing capabilities. To avoid confusion, you should call it
>>what it is.
>>
>
> Oh my, sorry. It is an 8-port 10/100Mbps Ethernet Switch! How does that change
> anything?
It really doesn't (you don't want a router in that location, you
want a switch). A router connects multiple IP subnets that otherwise
cannot talk to one another. Turning on the gateway feature on your
FreeBSD box makes it a two-interface router. A switch merely
multiplexes packets on many ports (it's a signal repeater/amplifier).
[snip]
> Oh, my sorry! Yes, the default gateway is set and I have no firewall to
> complicate matters.
Ah... I see the problem now. You *MUST* do NAT on your BSD gateway,
unless you personally control the configuration of your DSL router
and can give it the necessary routing instructions to find your 172
network.
You are trying to ping your DSL router from a private network
address that the router does not know about. The ping will reach the
DSL router and it will not know where to send the reply because your
private address does not (cannot) exist in its routing table. So, it
sends the reply on its default route, which is towards the Internet.
Bye, bye ping reply!
Again, this is just very basic networking stuff. I didn't see it
before because I route packets between private networks all the time
and it works -- the difference is that all my routers are
well-informed about the pathways to all nearby networks.
For the background information you need to know, buy this or find it
at your local library: http://www.oreilly.com/catalog/tcp3/
I'm sure there are other and even better titles.
--
Greg Barniskis, Computer Systems Integrator
South Central Library System (SCLS)
Library Interchange Network (LINK)
<gregb at scls.lib.wi.us>, (608) 266-6348
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