Interference between two wireless cards in one PC?

23 Feb 2005 10:03 AM

Terje_Midtbø

Hi!

I am using the following configuration:

Two desktop computers communicating trough a wireless network (ad-hock)
(Cards: Gigabyte GN-WPKG).

In one of the computers it is also installed another wireless card
(D-link g520+) with an external antenna. This card is connecting me to
the Internet (distant accesspoint)

Problem:

The ad-hock (peer-to-peer) communication between my two computers seems
to work fine when my Internet connection is disabled. However, when I
connect to Internet trough the D-link, the ad-hock communication fails.
The ad-hock is WEP encrypted on channal 3, while the external
communication is trough VPN on channal 1 or 11 (depends on link quality...).

Any suggestion on wath I can do to run both networks at the same time?

terjem

23 Feb 2005 5:50 PM

Jeff Liebermann

On Wed, 23 Feb 2005 11:03:28 +0100, Terje Midtbø <ter***@ntnu.no>
wrote:

Show quoteHide quote

>Two desktop computers communicating trough a wireless network (ad-hock)
>(Cards: Gigabyte GN-WPKG).
>
>In one of the computers it is also installed another wireless card
>(D-link g520+) with an external antenna. This card is connecting me to
>the Internet (distant accesspoint)
>
>Problem:
>
>The ad-hock (peer-to-peer) communication between my two computers seems
>to work fine when my Internet connection is disabled. However, when I
>connect to Internet trough the D-link, the ad-hock communication fails.
>The ad-hock is WEP encrypted on channal 3, while the external
>communication is trough VPN on channal 1 or 11 (depends on link quality...).
>
>Any suggestion on wath I can do to run both networks at the same time?

If you're on different non-overlapping channels, there will be little
interference. The three non-overlapping channels are 1, 6, and 11.
However, Ch 3 overlaps onto Ch 1. Therefore, I suggest you move your
Ad-Hoc network to Ch 6.

The mostly likely culprit is that your route changes when connected to
whatever wireless access point appears and is probably the remote
gateway for the VPN. Assuming you're running some Windoze mutation,
from an MSDOS window, run:
route print
to dump routeing table. Try to figure out where you packets are
really going. If you're not sure, try running:
tracert ip_address
where IP_address is some address on the internet. It might show the
route packets take to get through the VPN, to the internet, etc.

Also, I once threw together a wireless repeater crafted from a pair of
DWL-520 PCI cards in one machine. The antennas were about 2" apart.
The radios were on Ch 1 and Ch 11 for isolation. There was no obvious
RF interference problems with this arrangement, although I didn't do
much testing beyone moving the antennas around and using the site
survey tool to check for S/N deterioration.

--
Jeff Liebermann    je***@comix.santa-cruz.ca.us
150 Felker St #D   http://www.LearnByDestroying.com
Santa Cruz CA 95060    AE6KS 831-336-2558

23 Feb 2005 10:29 PM

Terje_Midtbø

Thank you for your answer. This evening I have done some more research,
and it sems like my local peer-to-peer network goes down the moment my
VPN connection is established. When close down the VPN my local network
is OK again. I have tried to generate some network activity without the
VPN, and it does'nt seme to influence on my local network.

Any suggestion on what I can do?

terjem

Jeff Liebermann wrote:
Show quoteHide quote

> On Wed, 23 Feb 2005 11:03:28 +0100, Terje Midtbø <ter***@ntnu.no>
> wrote:
>
>
>>Two desktop computers communicating trough a wireless network (ad-hock)
>>(Cards: Gigabyte GN-WPKG).
>>
>>In one of the computers it is also installed another wireless card
>>(D-link g520+) with an external antenna. This card is connecting me to
>>the Internet (distant accesspoint)
>>
>>Problem:
>>
>>The ad-hock (peer-to-peer) communication between my two computers seems
>>to work fine when my Internet connection is disabled. However, when I
>>connect to Internet trough the D-link, the ad-hock communication fails.
>>The ad-hock is WEP encrypted on channal 3, while the external
>>communication is trough VPN on channal 1 or 11 (depends on link quality...).
>>
>>Any suggestion on wath I can do to run both networks at the same time?
>
>
> If you're on different non-overlapping channels, there will be little
> interference. The three non-overlapping channels are 1, 6, and 11.
> However, Ch 3 overlaps onto Ch 1. Therefore, I suggest you move your
> Ad-Hoc network to Ch 6.
>
> The mostly likely culprit is that your route changes when connected to
> whatever wireless access point appears and is probably the remote
> gateway for the VPN. Assuming you're running some Windoze mutation,
> from an MSDOS window, run:
>   route print
> to dump routeing table. Try to figure out where you packets are
> really going. If you're not sure, try running:
>   tracert ip_address
> where IP_address is some address on the internet. It might show the
> route packets take to get through the VPN, to the internet, etc.
>
> Also, I once threw together a wireless repeater crafted from a pair of
> DWL-520 PCI cards in one machine.   The antennas were about 2" apart.
> The radios were on Ch 1 and Ch 11 for isolation. There was no obvious
> RF interference problems with this arrangement, although I didn't do
> much testing beyone moving the antennas around and using the site
> survey tool to check for S/N deterioration.
>
>

24 Feb 2005 6:31 AM

Jeff Liebermann

On Wed, 23 Feb 2005 23:29:57 +0100, Terje Midtbø <ter***@ntnu.no>
wrote:

>Thank you for your answer. This evening I have done some more research,
>and it sems like my local peer-to-peer network goes down the moment my
>VPN connection is established. When close down the VPN my local network
>is OK again. I have tried to generate some network activity without the
>VPN, and it does'nt seme to influence on my local network.
>
>Any suggestion on what I can do?

Several possibilities.

1. Your routes change when you connect to the VPN. Run:
route print
before and after connecting to the VPN. See where your local packets
are going. Post both results and we can help. While you're at it,
kindly disclose what operating system you're using, what version, what
VPN client, what version, what wireless service you're using, IP
address assignments, and anything else that might seem useful.

2. You configured your ad-hoc network to be the same as the VPN IP
block. If your VPN delivers an IP address as 192.168.22.xxx from its
IP address pool, then you should NOT use 192.168.22.xxx for the ad-hoc
network. The 192.168.xxx.xxx is fine, but don't re-use
192.168.22.xxx. Depending on the client and/or OS, your routing will
be a mess. Run:
ipconfig /all | more
to see what IP addresses are assigned to which interfaces.

3. Isolating the VPN traffic from the rest of the network is a
security feature of many VPN clients. For example, the Boigo wireless
client disconnects the user from anything outside the VPN address
space. This is normally a good thing as it protects against client to
client hacking and worm distribution. In a host spot environment,
there's also no reason to connect to other nearby clients.

Methinks #3 is the most likely, especially if you're using Boingo.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
# je***@comix.santa-cruz.ca.us
# je***@cruzio.com AE6KS