Wireless network effected by duplicate IP addy's

Posted on 2011-02-18
Last Modified: 2012-05-11
I'm helping out an office that is using several tablets & laptops over a wireless network. They are having problems with disconnections & reconnecting while moving throughout their office.

They are using the router default IP of I would like to know if there are other offices in their building using the same subnet for their network, would that create any interference on their network even though all of the networks have different SSID's & WPA security settings.
Question by:Blinkr
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Expert Comment

ID: 34930762
The IP-addressings won't of wireless networks won't affect each other. You won't even be able to check the IP-addresses of the other wireless networks unless they are open or you have their encyption keys. The access points of different networks may interfere each other if they happen to use the same channels (frequencies).

Most wireless interface cards include some sort of diagnostics software that let you look for detected WiFi networks and their channels. You could use a laptop equipped with one of these and walk around the office, especially in those locations suffering from disconnections and check what you see there. While doing that you can and should also check the signal strength of the intended network. Wireless networks are not very reliable in many environments due to signal fading caused by building structures, unless they are very carefully implemented with multiple access points covering all the areas.

LVL 13

Assisted Solution

kdearing earned 125 total points
ID: 34933326
Interference is caused by other devices operating on the same or similar frequency.
If you are getting interference, it could be caused by another wifi network.
Other common sources are cordless phones and microwave ovens.

Use Netstumbler on your laptop to see what your wireless environment looks like.

Assuming your wireless is b/g/n, there are only 3 non-overlapping channels: 1, 6, & 11
Configure your wireless to whichever of those 3 that gets you the best signal.
LVL 24

Accepted Solution

rfc1180 earned 125 total points
ID: 34933750
kdearing brings up several good points relating to the issue you are having;

>Interference is caused by other devices operating on the same or similar frequency.

Depending on the wireless network design (In General) you can have a very reliable network. I have designed countless wireless networks and have yet to have a customer call back in for anything that was related to connectivity issues, etc. My point being is have patience, take the time to analyze the issue, identify the issue, troubleshoot the issue, and move on with other facinating things that you do in your life! Great points have been presented, get netstumbler; however, I like inSSIDer; along with a floor map of the building floor (Hard to find, but most buildings have a floor map/plan of the building or office area for emergency evacuation purposes that you can use as a generic map). Map out the dbm levels in the office by walking  around. You will want to stay within -65dBm and -68dBm as most vendors will have a recieve sensitivity that matches those levels. You will also want to take the signal to noise ratio of the environment as well, if the interference (noise) is very close to the received signal level of the AP, the AP will have a hard time understanding which signal is which.


Author Comment

ID: 34933764
AriMC, thanks for that info. I was fairly sure of all of this but wanted an experts opinion. When I was checking the networks close by, nothing should up on their channel (3).

Thanks, kdearing. I am going to run Netstumbler in their office next week to see what going on.

I haven't had a chance to check what they have told me, but they claim that they have about 4-5 access points in ceiling spread out the office. would putting these access points in the ceiling have any effects on wireless service?? They do have flourescent lights & 10 ft. drop ceilings.
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Author Comment

ID: 34933798
Thanks rfc1180! Would the fact that they have about 4-5 ap in a drop ceiling throughout the office create any issues?

Thanks also for the suggestion for the inSSIDer. The more tools, the better the info.
LVL 13

Expert Comment

ID: 34933808
In my experience, the ideal height is 8-10'
With flourescent lighting, make sure the access points are not mounted too far above the ceiling.
I prefer to use the "smoke detector" style antennas mounted in the ceiling.
LVL 24

Expert Comment

ID: 34933889
>about 4-5 ap in a drop ceiling throughout the office create any issues?
only issue is decreased in signal due to absorption of the ceiling; Typically, the APs are mount on the drop ceiling, and ceilings are about 10.8 feet. You want to stay between 10.8 and 25 feet, any higher, you will start to see some issues. What kind of APs do you have, do they have an option for external antennas, you could get a patch antenna, such as: and leave the AP in the ceiling.


Author Comment

ID: 34934064
kdearing, that's a great suggestion. I will look for those antennas.

rfc1180, thanks as well. I have had a chance to look inside the ceiling yet. I'm working off what the office manager is telling me. Most of their equipment is either Linksys or Cisco that I have seen. So I'm assuming that the ap's are as well. The external antennas are a good idea. The one you suggested is similar the one that kdearing suggested.

Thanks again guys for the help!

Author Closing Comment

ID: 35098032
I got the InSSIDer & purchased the Wi-Spy 2.4. This is helping out alot. I'm finding interference in several locations in the office. I haven't found a database of signatures from Metageek yet but have been storing up many that others are sharing. This is a great program with or without the Wi-Spy. Thanks for all of the help!!

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