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Re: [tlug] LAN, but no internet

Dave M G writes:

 > Something about how the wireless and wired networks are talking to
 > each other is still not clear.

I think what you're missing is that in most cases routers function as
gateways between logically different networks (which almost always are
on separate wires[1]) and therefore are multihomed; that is, they have
multiple addresses.

Ie, the network looks like this, where global IPs are denoted by
single-digit quads (eg, and LAN (non-routable) IPs are
denoted by Class C private IPs (eg,  Each address can be
used only on the "wire" (including wireless channel) leading to it.
(Strictly speaking, not quite true, but we can talk about that later
if you care to.)

                             THE INTERNET
                           |   |
                           | ISP gateway |    (far, far away)
                           |   |
                           |   |
                           |  ISP modem  |    (in your closet)
                           | |
                           | |
                           |  wireless   |    (sitting on a shelf)
                           | |
                           | |
                           |    laptop   |    (on your desk)

I don't think it is possible for a router to have the same IP address
on two networks that are logically different.  So you could set up
"wireless" as transparent bridge with no address of its own (all
packets are simply relayed to the appropriate interface), or you can
set it up as a gateway, but then it must have two separate addresses:
one facing the ISP's modem, and one facing the client host.

It must be possible to distinguish the two logical networks by masking.
Not necessarily by class, but all of the addresses on the laptop side
of wireles must share a prefix of N bits for 0 < N < 32.  There are
some practical considerations that mean that N < 31 (ie, the smallest
possible networks have 4 addresses, one of which is conventionally the
network address (in practiced, simply wasted AFAIK), another is the
broadcast address, leaving two host addresses.

Re: your problem: try filling in the above diagram for your own
network.  Routers and gateways should have two IP addresses,
workstations only need one.  Once you've done that, you probably will
be able to figure out for yourself what needs done next.  If you
become convinced that your wireless only has one address, you'll need
to come back and ask, I suppose.

[1]  It's much easier to create a single logical network with multiple
wires by bridging.

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