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Home networks interfere with Community Network

Discussion in 'Networking' started by CarolinaBill, Dec 5, 2011.

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  1. CarolinaBill

    CarolinaBill Thread Starter

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    I live in a retirement community that has been struggling with setting up a community wireless network system for its residents. The network technicians have been plagued by problems arising from many residents having home networks of many varieties -- some have retained legacy connections to dial-up and cable modem access to the internet, others connected to the new community system (which is called RESNET). The residents in question vary even more widely in their computer literacy ranging from those who barely know how to turn on a computer their grandson may have brought to them, while others are quite sophisticated. The RESNET network has dozens of separate wireless access points scattered through the buildings and communicating by roof-top antennas with separate cottages. It makes use of almost all channels from 1 to 11. Access control is by MAC addresses for individual residents' computers (or actually a wireless adapter on the computer). There are a couple hundred computers connected to the system plus a significant number of residents still connected to our previous cable network supplier.

    I have ranked the different types of networks in order of possible interference according to my view.
    1. It is my understanding that if residents have a home network that is security-protected, there should be no communication in either direction with RESNET and should not interfere unless the strength of its signal overwhelms that of the corresponding channel of the RESNET system.

    2. There are a number of home networks that are unsecured and are accessible by neighbors if any of them were so inclined. But unless that network was set up to broadcast DHCP addresses to neighboring antennas, I would think that type of network should not interfere with the overall system.

    3. There have been several networks located that have DHCP enabled that have sent IP addresses to neighbors who are simply connecting to the nearest and strongest signal. That indeed is a problem. In a couple cases those have been identified and the DHCP disabled.

    4. There are a few home networks that have adopted the name RESNET for their home network not knowing better.
    I am not sure how that is affecting the community system. The owners of these networks do not know better and so it is difficult to identify them. Given time, the network technicians should be able to identify them by going around the campus with a laptop and network sniffer and picking up the signal for any RESNET network that is of different manufacture.

    Do those of you who have experience with mixed networks like this have any strategy to suggest to get the problems under control.
     
  2. TerryNet

    TerryNet Moderator

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    1. Not true. Interference is a function of channel (frequency) and signal strength. Has nothing to do with security.

    2. See number 1.

    Depends on how much control the community has over the residents. Should outlaw (or request avoiding) the use of RESNET for their SSID. Could outlaw the use of wireless routers or access points other than the community system.
     
  3. Steve_oh

    Steve_oh

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    Unless there is something I am missing, there is no "interference" only confusion. Some community members attempting to connect to the community system may actually be connecting to the non-community systems mistakenly broadcasting the RESNET ssid. If there is genuine interference, it is likely electrical as in building wiring not another network.

    It is possible to just knock on some doors and ask the residents if they have a wireless router. If they do, verify the SSID. If they are using RESNET, ask/advise them to change it or offer to change it for them.
     
  4. TerryNet

    TerryNet Moderator

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    Do you have any experience with Wi-Fi? Why would you suspect electrical interference? Why would you not expect some wireless interference from networks on the same or close channel to a nearby community network AP?
     
  5. Steve_oh

    Steve_oh

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    True my Wi-Fi experience is limited but I would expect packet addressing to handle that type of cross-talk. I am saying the duplicated SSID within the community is the area to look at.
     
  6. TerryNet

    TerryNet Moderator

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    You would be wrong. :) Two networks on the same channel with the same signal strength is sorta like having two people side by side talking to you. Sure, you should be able to filter out what one is saying and concentrate on and understand every word spoken by the one you want to hear, but in practice you probably won't succeed for long.
     
  7. CarolinaBill

    CarolinaBill Thread Starter

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    Sorry to be slow in responding but I have been off the internet for the last day and a half. This was partly caused by a problem I have never seen before. I can access three RESNET access points which are antennas operating on different channels, located on top of three buildings and which vary somewhat in signal strength. Yesterday I was surprised to have one antenna return a DNS address of 192.168.1.251 which is obviously some kind of default value from a private router. Normally we are served by Time-Warner's southeastern regional DNS of 24.25.5.60. Repeatedly if I connected with that one access point, my DNS address was set to the 192 value. I tried putting in the correct DNS as a static value, but that was deleted and my network adapter properties were kicked back to automatic setting of DNS. This DNS value is obviously entering my computer through the RESNET network since my home network is secured. How can a sub-network impose its DNS value on the server for the main network?

    To reply to comments so far: I agree completely that we need to get rid of any private networks with an SSID of RESNET. Fortunately I don't think there are more than two or three but it may take the technicians a little time to locate them.

    As to network interference, how close would an interfering device need to be? And how far back up the chain of communication would that have an effect -- everything operating on that channel, or only devices that are physically fairly close? We have a number of instances where a wireless router in an apartment, operating say on channel 2, might send a fairly substantial signal through the walls into the corridor where a system access point is located. The system uses almost all of the channels from 1 - 11 in different parts of the property. Would interference be more or less unidirectional, that is affect mainly the device that is connected to RESNET, or would it be bidirectional and interfere with all the other defices that are connecting to that same access point?

    We have a substantial number of networks that can be seen at a time depending on the time of day and the part of the campus where a check is made. Most of the time, neighboring networks have significantly less strength than the particular RESNET antenna I connect to. For example, as I write this, I can see a variety of networks located within a 100-yard radius:
    Network Channel Security Strength
    RESNET 2 None 68%
    (Mine) 3 Yes 96%
    RESNET 4 None 64%
    private 6 None 54%
    private 6 Yes 68%
    RESNET 9 None 78% Usual connection for me
    RESNET 10 None 76% Frequently useable as an alternative
    private 11 Yes 66%
    private 11 Yes 40%
    RESNET 11 None 74% Occasionally useable by me
    (The strengths vary each time I refresh, but these are representative, and not all of the private networks are broadcasting at the same time.
    I would assume that the other networks are sufficiently far away and of sufficiently less strength that I should not expect any direct interference on my own network.

    I have further questions but will stop here and look for any comments on my observations of our system so far.
     
  8. TerryNet

    TerryNet Moderator

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    For Windows systems the Networks page of the Xirrus Wi-Fi Inspector is the best tool I've experienced for seeing the available networks and their relative strengths and propensity to interfere. If you post a screen shot with questions we can help interpret it.
     
  9. CarolinaBill

    CarolinaBill Thread Starter

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    I can't get on my own internet right now and have to communicate using another computer, so I can't send you a screen shot of Xirrus right now. But I don't believe any of the networks showing there are responsible for some of the problems we are having. For example, using the example of the list of networks given in my communication earlier, I can connect to Channel 9, receive an IP and DNS address and make connection without trouble. But then consistently for the past couple of weeks, that channel was unable to ping the DNS address and complete and internet connection. For most of last week, I could connect to Channel 10 even though it had a little less strength and connect okay. This week, connecting to that same channel (which is about 180 degrees directionally from Channel 9) results in a failure to send an IP address. Eventually, my adapter sets up a 169.x.x.x address. If I use a static IP and try to connect, that is over-ridden and my adapter properties are changed by the remote location to automatic. My conclusion is that none of the networks that are within my circle of recognition are causing problems and that it is something upstream from the Channel 9 and Channel 10 access points. This is somewhat similar to that fact that on occasion Channel 11 was sending out a DNS address of 192.168.1.251,
     
  10. CarolinaBill

    CarolinaBill Thread Starter

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    I have another question. If a computer can connect with a client network within the main network, is there some command or software that allows one to determine the SSID of that network's access point, or IP address, or channel #. Our system technicians have been trying to locate a network that is unwittingly shutting down the system and they know the network name, but they have not been able to connect it with an SSID that they might trace electronically.
     
  11. TerryNet

    TerryNet Moderator

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    I don't know what a "client network within the main network" is.

    Every wireless utility I have ever used with Windows 7, Vista, XP and Ubuntu and Puppy Linux has identified the SSID of any wireless network to which I have been connected. Typically the wireless utility will also show the channel. Xirrus will show both. I don't know of any general way to identify an Access Point's IP address.

    I do not understand. The SSID is the name of a wireless network.
     
  12. zx10guy

    zx10guy Trusted Advisor Spam Fighter

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    From the sounds of it, you don't have a enterprise level wireless system. You probably need a system which uses a wireless controller and light weight access points. These systems do automatic channel hopping to ensure the AP is providing the best signal for connectivity. These systems also have a security feature called rogue AP detection. What the APs will do is to do a RF map of your area. You can then overlay building plans onto the RF map and overlay a physical boundary to the RF map. The APs work together and provide triangulation information to identify broadcasting devices in the defined area. If a rogue AP is detected, it can either log and alert you or proactively shut it down. The shut down of the AP can be done in a number of ways. One of the methods is similar to a denial of service attack which prevents any client from completing an association with that AP.

    The accuracy of these systems can be very good to under a couple of feet of resolution or better. Plus they can also do it in all three dimensions.
     
  13. CarolinaBill

    CarolinaBill Thread Starter

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    Thanks zx10guy. I have passed on your comments to our systems people. They supposedly have upgraded
    from a 500-user system to a 4K-user enterprise system, but apparently don't have some of the other tools to
    go with it.
     
  14. CarolinaBill

    CarolinaBill Thread Starter

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    TerryNet, I guess I used the wrong term. What I meant that the workgroup name for the private network
    is known, but the SSID is not known.
     
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