Cannot set up ICS

[Guest]

I received the following message when I tried to set up a home network on the
host computer using the Network Setup Wizard:

"Windows cannot set up this computer to share its internet connection
because the IP address it needs (192.168.0.1) is being used by another
computer or device on the network, or by software running on this computer."

I'm trying to connect my PC and laptop (both running Win XP SP2) to share an
internet connection. I also have a printer on the network. I'm using a USB
DSL modem and connect the two PCs to a router.

How can I find out which device or software is preventing the host computer
from acquiring the required IP address? I've checked and my laptop is not
using the required IP address.

Thanks in advance.

 

[Doug Sherman [MVP]]

The 192.168.0.1 address is probably the router. If this is a NAT router and
you can connect the modem to the WAN (Internet) port of the router, then you
do not need ICS in this scenario.

Doug Sherman
MCSE Win2k/NT4.0, MCSA, MCP+I, MVP

 

[Guest]

hmm...the problem is, I cannot connect the USB modem to the router. The USB
plug on my modem goes to the USB port on my PC and there's a phone jack for
the telephone line. That's it, nothing on the modem that connects to the
router directly.

So I figured out I'll have to set up ICS. Any way to assign a different IP
address to the router?

 

[Bob Willard]

hmm...the problem is, I cannot connect the USB modem to the router. The USB
plug on my modem goes to the USB port on my PC and there's a phone jack for
the telephone line. That's it, nothing on the modem that connects to the
router directly.

So I figured out I'll have to set up ICS. Any way to assign a different IP
address to the router?

With most routers, you can change the LAN-side IPA. Log into the router, and
look at its configuration pages.

The down side is that whenever you do a hard reset on the router, it may
return to its default IPA: to recover from that, you'll need to turn off
ICS, then change the router's IPA, then turn ICS back on.

 

[AGS]

Question...I'm having similiar ICS connectivity problems between a
deskop and laptop and was wondering, is there no way to change the
default static IP on the ICS host that Windows XP assigns? In my case,
I know 192.168.0.1 is my router and I can change the router address if
needed...but i'd rather not since it would require me to change the
default gateway on all my networked PC's (all static).

Currently i'm trying to setup ICS between a deskop (which connects
wireless to the router; XP Home) and a laptop (2000 Pro). From the
laptop, I'm able to ping the desktop and see all shared files/folders on
the desktop. My last step (i'm assuming) is to share the wireless
internet connection on the desktop so the laptop can access the net.
But i'm running into the same error when I attempt to share the
connection, hence, my question about the default static IP.

Thanks.

-AGS

 

[Bob Willard]

Question...I'm having similiar ICS connectivity problems between a
deskop and laptop and was wondering, is there no way to change the
default static IP on the ICS host that Windows XP assigns? In my case,
I know 192.168.0.1 is my router and I can change the router address if
needed...but i'd rather not since it would require me to change the
default gateway on all my networked PC's (all static).

Currently i'm trying to setup ICS between a deskop (which connects
wireless to the router; XP Home) and a laptop (2000 Pro). From the
laptop, I'm able to ping the desktop and see all shared files/folders on
the desktop. My last step (i'm assuming) is to share the wireless
internet connection on the desktop so the laptop can access the net. But
i'm running into the same error when I attempt to share the connection,
hence, my question about the default static IP.

Thanks.

-AGS

ICS does not allow you to change the IPA it uses for itself (the ICS server)
or the range of IPAs it hands out to ICS clients.

Most routers do allow you to change their LAN-side IPA. But, when you
need to hard-reset the router, the IPA may revert to its default value.

Since you have a router, I don't understand why you also want to use ICS.
Hardware routing is more robust than software (ICS) routing, and avoids
the conflict over 192.168.0.1.

 

[AGS]

ICS does not allow you to change the IPA it uses for itself (the ICS
server)
or the range of IPAs it hands out to ICS clients.

Most routers do allow you to change their LAN-side IPA. But, when you
need to hard-reset the router, the IPA may revert to its default value.

Since you have a router, I don't understand why you also want to use ICS.
Hardware routing is more robust than software (ICS) routing, and avoids
the conflict over 192.168.0.1.

Thanks for the reply.

The reason i'm using ICS in between this particular desktop and laptop
is because the laptop is too far away from the router to be plugged in
directly and it has no wireless card. Granted, I could go out and buy a
wireless card for it but thought it would be more cost effecient if I
could get the ICS up and running between the two.

So from my understanding, since the default IPA with ICS cannot be
changed, there can only really be one ICS up and running at any given
time. If I attempt to setup ICS on another pair of PC's in my
home-office, it probably wouldn't work since there is already a PC on
the network with the static IP of 192.168.0.1. Is this assumption correct?

-AGS

 

[Bob Willard]

Thanks for the reply.

The reason i'm using ICS in between this particular desktop and laptop
is because the laptop is too far away from the router to be plugged in
directly and it has no wireless card. Granted, I could go out and buy a
wireless card for it but thought it would be more cost effecient if I
could get the ICS up and running between the two.

So from my understanding, since the default IPA with ICS cannot be
changed, there can only really be one ICS up and running at any given
time. If I attempt to setup ICS on another pair of PC's in my
home-office, it probably wouldn't work since there is already a PC on
the network with the static IP of 192.168.0.1. Is this assumption correct?

-AGS

That depends on the physical connectivity. For example, suppose A, B, C, and
D are PCs and R is a Router (with connectivity to the external 'net). If the
connections look like this:

A<===>B<===>R<===>C<===>D
|
+------------------> WAN-side link, to the 'net

and B is the ICS server for A, and C is the ICS server for D, then both B and
C can use the normal 192.168.0.1 ICS server IPA, and both B and C can assign
192.168.0.2 to A and D, *as long as* R is not using the 192.168.0.1 IPA on its
LAN side. The key is that 192.168.0.x are non-routable IPAs: C and D know that
192.168.0.1 belongs to C, but that information is hidden from A, B, and R; also,
A and B know that 192.168.0.1 belongs to B, but that infomation is hidden from
C, D, and R. {If R also tries to use 192.168.0.1, then B and C know about two
nodes with the same IPA: B knows about R and itself, and C knows about R and
itself -- that is a no-no.}


If the above diagram does not make sense to you, note that B and C both have
two NICs and each NIC has its own IPA: one is the downhill NIC/IPA to its
ICS client, and one is the uphill NIC/IPA to the router. And, it makes no
difference whether those connections are wired or wireless.

{Ain't ASCII-art wonderful?}

 

[AGS]

That depends on the physical connectivity. For example, suppose A, B,
C, and
D are PCs and R is a Router (with connectivity to the external 'net).
If the
connections look like this:

A<===>B<===>R<===>C<===>D
|
+------------------> WAN-side link, to the 'net

and B is the ICS server for A, and C is the ICS server for D, then both
B and
C can use the normal 192.168.0.1 ICS server IPA, and both B and C can
assign
192.168.0.2 to A and D, *as long as* R is not using the 192.168.0.1 IPA
on its
LAN side. The key is that 192.168.0.x are non-routable IPAs: C and D
know that
192.168.0.1 belongs to C, but that information is hidden from A, B, and
R; also,
A and B know that 192.168.0.1 belongs to B, but that infomation is
hidden from
C, D, and R. {If R also tries to use 192.168.0.1, then B and C know
about two
nodes with the same IPA: B knows about R and itself, and C knows about
R and
itself -- that is a no-no.}


If the above diagram does not make sense to you, note that B and C both
have
two NICs and each NIC has its own IPA: one is the downhill NIC/IPA to its
ICS client, and one is the uphill NIC/IPA to the router. And, it makes no
difference whether those connections are wired or wireless.

{Ain't ASCII-art wonderful?}

ASCII-art is wonderful, indeed.

A<===>B<===>R<===>C<===>D

Ok, I follow the diagram but still having difficulty understanding how B
and C would not know about each other if they connect to the same router
and are on the same domain. For example, lets say we add two more PCs
to the diagram, E and F, and neither are setup for ICS.

E
|
A<===>B<===>R<===>C<===>D
|
F

E has the IPA of 192.168.0.6 and F has the IPA of 192.168.0.7. E and F
can see each other on the network and both have their own respective
wired/wireless connection to R. So how is it that B and C would not?
If I were to go to either E or F and say ping 192.168.0.1, whom would
respond?

Thanks again for the response.

-AGS

 

[Bob Willard]

ASCII-art is wonderful, indeed.

A<===>B<===>R<===>C<===>D

Ok, I follow the diagram but still having difficulty understanding how B
and C would not know about each other if they connect to the same router
and are on the same domain. For example, lets say we add two more PCs
to the diagram, E and F, and neither are setup for ICS.

E
|
A<===>B<===>R<===>C<===>D
|
F

E has the IPA of 192.168.0.6 and F has the IPA of 192.168.0.7. E and F
can see each other on the network and both have their own respective
wired/wireless connection to R. So how is it that B and C would not? If
I were to go to either E or F and say ping 192.168.0.1, whom would respond?

Thanks again for the response.

-AGS

Let's take the case of B, the ICS server for A. B has two NICs (one to connect
to A and one to R), and each NIC has its own IPA. The IPA for ICS, 192.168.0.1,
is visible to B and to A, but -- since it is a non-routable IPA -- it is not
visible to R (or C, D, E, or F). By not visible, I mean that an IP packet with
a destination IPA of 192.168.0.1 when delivered to B through the NIC that connects
to R will be discarded: it will not be routed (by B) from its right-hand NIC to
its left-hand NIC. {A classic example of the saying that the left hand does not
know what the right hand is doing. ;-) }

As for the ping question: if the 192.168.0.1 network above is properly
configured, then when E pings 192.168.0.1, nobody will respond. In an improper
configuration, with R using 192.168.0.1 as its LAN-side IPA, then when E pings
192.168.0.1, R will respond; however, when B pings 192.168.0.1, there are *two*
potential responders -- B and R -- which is why this configuration is improper.
That illustrates why, in the A/B/C/D/E/F/R network above, you must not allow
R to use 192.168.0.1 if nodes connected to R are also ICS servers.

If you want to create a network like A/B/C/D/E/F/R with R using 192.168.0.1 as
its LAN-side IPA, then you must not use ICS. There are some non-M$ products
that do software routing but are more flexible than ICS; none come to mind, but
you can Google.

 

[AGS]

Let's take the case of B, the ICS server for A. B has two NICs (one to
connect
to A and one to R), and each NIC has its own IPA. The IPA for ICS,
192.168.0.1,
is visible to B and to A, but -- since it is a non-routable IPA -- it is
not
visible to R (or C, D, E, or F). By not visible, I mean that an IP
packet with
a destination IPA of 192.168.0.1 when delivered to B through the NIC
that connects
to R will be discarded: it will not be routed (by B) from its
right-hand NIC to
its left-hand NIC. {A classic example of the saying that the left hand
does not
know what the right hand is doing. ;-) }

As for the ping question: if the 192.168.0.1 network above is properly
configured, then when E pings 192.168.0.1, nobody will respond. In an
improper
configuration, with R using 192.168.0.1 as its LAN-side IPA, then when E
pings
192.168.0.1, R will respond; however, when B pings 192.168.0.1, there
are *two*
potential responders -- B and R -- which is why this configuration is
improper.
That illustrates why, in the A/B/C/D/E/F/R network above, you must not
allow
R to use 192.168.0.1 if nodes connected to R are also ICS servers.

If you want to create a network like A/B/C/D/E/F/R with R using
192.168.0.1 as
its LAN-side IPA, then you must not use ICS. There are some non-M$
products
that do software routing but are more flexible than ICS; none come to
mind, but
you can Google.

All my questions are answered. Thanks for all the great information.

BTW, I ended up dropping the whole ICS between my desktop and laptop. I
changed the router IPA and verified that none of the PCs on the network
were using 192.168.0.1, but any attempt to share the ISP connection on
my desktop failed with Windows complaining that the 192.168.0.1 was in
use. Not sure what was causing the conflict. Friend of mine had an
extra 802.11b wireless card laying around and ended up using it to setup
the laptop on the network. All is now well.

-AGS

 

[Bob Willard]

All my questions are answered. Thanks for all the great information.

BTW, I ended up dropping the whole ICS between my desktop and laptop. I
changed the router IPA and verified that none of the PCs on the network
were using 192.168.0.1, but any attempt to share the ISP connection on
my desktop failed with Windows complaining that the 192.168.0.1 was in
use. Not sure what was causing the conflict. Friend of mine had an
extra 802.11b wireless card laying around and ended up using it to setup
the laptop on the network. All is now well.

-AGS

Glad to have helped.