Re: One or two questions.

"Jeff Gaines" <jgaines_newsid@xxxxxxxxxxx> wrote in message
news:xn0f3rw9hefofsk000@xxxxxxxxxxxxxxxxxxxxxx
On 16/03/2007 in message
<DwoKh.6477$DX5.5749@xxxxxxxxxxxxxxxxxxxxxxxxxx> pmj wrote:
"Jeff Gaines" <jgaines_newsid@xxxxxxxxxxx> wrote in message
news:xn0f3rhprdvx1k7000@xxxxxxxxxxxxxxxxxxxxxx

My WAP is able to get an address from a DHCP server - but it's
not the default.

If it does get an IP Address from a DHCP Server, isn't that the
WAN (Internet) IP Address?
& not the (Private) IP Address that it uses on the LAN?

Or have I got this all wrong?

I don't know about wrong but it's confusing me :-)

LOL!
Me too!!!

But I would like to try & understand what goes on...

<snip>
I don't think a router can have 2 IP addresses. If it gets its
address from a DHCP server then thats its address.

No, surely that's where you're wrong?

A Router, very specifically does ahve 2 (different) IP Addresses?

One is the WAN (Wide Area Network - usually the Internet) IP Address
Which it gets from whatever it's connected to (a Cable or ADSL Modem
or whatever) using its DHCP Client...

& one (which is its own (Private) IP Address on teh Lan, which it is
Set to use (or it chooses for itself & then it dishes out (Allocates)
IP Addresses to the things that Connect to it using its DHCP Server
(or the things can be Set with their own IP Address, but they all do
still have to be in the same Subnet)

OK, this may be the root of the confusion.

Yep, I think it prolly is.

... In the case where the new router/WAP is plugged into the existing
modem I envisage it working effectively as a dumb switch, i.e.
connected via one of its Ethernet ports, not the Internet port.

Yep, but (or and it's) *that* does seem to cause all sorts of probs!!!

... The signal conversion/NAT etc. happens at the modem

Hmmm...
I'm not sure about that?
Doesn't the Modem just pass the stuff (whatever comes in from either
side) straight through?
& isn't it the job of the *Router* to do the NAT - Network Address
Translation - stuff?

But if the "Modem" that you are talking about is actually a Modem with
a Router Combined (which is the case with a typical ADSL Modem/Router)
then yes, there is potential for probs (as we know & have found out!)

... and is presented on its Ethernet port for distribution round the
LAN. If the signal presented at that port is something different then
presumably it will be presented to the Internet port of the router
which will do the routing.

Now I'm getting Confuzzled again.

Actaully I remember we had a discussion about this sort of thing a while
ago, didn't we?

I wondered if it would be possible to use a typical ADSL Modem/Router
as just a Router (say, with a cable Modem, or a standalone ADSl Modem)
& since that sort of (combined) Modem Router doesn't actually have a
separate (Ethernet) "Internet" (WAN) Port - it only has an ADSL Phone
Line Port, then how do you get access to what would be the "WAN" Port
of it?

No one seems to make any sort of (combined) ADSL Modem/Router that
*also* has a normal Ethernet Port for an Internet (WAN) Connection.

I can see that would be *very* useful, but there must be some reason
why they don't make them.

<snip>
if DHCP is required, it should be turned on at the modem and off
at the new router/WAP.

Nope.
I don't think so.

& I think, like you say, that's where our perceptions differ?
Yo utalk about "the Modem", but you are actually talking a (combined)
Modem/ *Router* aren't you?
& you don't actually have access to the Modem (or Router) parts of it
separately, do you?

By which I mean you can't access (using Ethernet) the LAN ("output"?)
side of the Modem bit of it.
& you can't actually access (using Ethernet) the WAN ("input"?) side
of it, can you?

With separate Modems & Routers (whether the Modem is a Cable Modem or
an ADSL one), you *can*!

& therefore what I was saying about there being different DHCP Clients
(& Servers) makes more sense (to me at least!)

<snip>
That's the key really. If the modem is dishing out a WAN address
to the router and is connected via the Internet port then that makes
sense, although I don't know what happens if you connect more than
one router.

Yep.
So (I think) that bit is clearer now?
:-)

If the modem has a WAN address one side and a LAN address on the
other then its DHCP should just be dishing out LAN addresses.

But a Modem (& not a combined Modem/Router) *doesn't* do that, does it?
That is done by the *Router*

Or if it *is* a combined Modem/Router, then yes, the *Router* bit of
it has a DHCP Server that dishes out the LAN Addresses

& it *also* has a DHCP *Client* which gets an *Internet* IP Address
from the upstream Connection (usually the ISP), via the *Modem* part
of it?

It means that donut must ensure that the new router/WAP can accept
an IP address from a DHCP server,

Which all the Routers I have used (& which I suggested she could use)
do.
But we (or I am) talking about the Router getting its WAN - Internet
IP Address using DHCP.

OK, but see above. What I meant was you don't want 2 DHCP servers
dishing out LAN addresses.

Exactly!
:-)

& she won't have.

The Router will be the (only) one dishing out the LAN Addresses.

<snip>
Only if it can. As I said my router needs a fixed LAN address -
and that's logical since the LAN needs to know where to go for
external routing information.

Yep.
But (& again, this is what Confuzzled both me & you, I think?)
the Router *does* actually have a DHCP *Client* in it, which obtains
its *WAN* IP Address from the "Upstream" DHCP Server - either the
Modem part of a combined one, or a separate Modem.
& the Modem DHCP "Server" may well (as Ali mentioned) actually be what
is basically a DHCP "Relay" - just passing on whatever Internet IP
Address is allocated by the ISP

If it works like that, then it all seems to make sense (to me)

... In addition if it's not the default then it will need changing.

It is the Default.

Again, not on my WAP, its default is a fixed address.

LOL!!!
But again, i think we are talking at cross purposes here!!!

The Router/WAP *does* have 2 (separate) IP Addreses, doesn't it?

The WAN (Internet) IP Address, assigned to it by the Modem/ISP & yes,
the *LAN* IP ADdress which is Set in it (or, as is the case with some,
you can define)
<snip>

I've had to snip a bit of this out, cos it's getting very unwieldy.

They are (surely?) 2 completely different things?

No. To manage the modem/router you need to connect to it via a
browser.

Yep.

If its default IP address is, say, 192.168.0.1 and your LAN uses
192.168.1.n addresses you won't be able to connect.

But doesn't that actually depend on the "Subnet Mask"?

Though I see what you are getting at?

You need to temporarily change the IP address on the PC, manage the
router/WAP (including changing its IP address to match the LAN) and
then change the PC's IP address back.

Yep, I found that out, when I tried a Buffalo thingy that I *thought*
was a Router/WAp, bu tactually it was (basically0 just a "Bridge" type
thing.

<snip>
I hope donut is following this, but also that she isn't put off by
us going into all this stuff about DHCP & IP Addresses etc...
:-)

Cos it really is easy & non-complicated actually to do!

We have enough knowledge to talk her through it,

Yep!
I'm sure we can, one way or another & am very confident of that!
:-)

... as long as she can switch back to her original configuration
to get Internet access if there's an issue.

Yep.
I did mention that in one of my other Replies.

& I also suggested that it would be a good idea, to do it step by
step...
First of all, Connect (just) the Caable Modem to (one of) the Pcs,
using the Ethenet Connection instead of the USB cable.
& *then*, when she's happy that that all works as it should, she can
get a WiFi Router & then Plug that in.


--
pmj


.

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