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wireless-networking interview questions

Top wireless-networking frequently asked interview questions

How to find a router at an unknown location in a house?

I want to install a WLAN repeater in my father’s holiday house which he rents out to other people.

My father is a digital neanderthal and doesn’t know where his router is, therefore I cannot configure my repeater to this router.

Are there any tools that could help me find that router in the house? I know that there are tools that tell you which Ethernet cable is in use and where it points to, so I figured maybe there are tools that help me find my router?

By “tools,” I don’t necessarely mean software, I’m also thinking about a hardware tool. I tried just going around with my cellphone and searching in the area with the best connection to the network but didn’t find the router.

Edit: Due to some comments that wanted more information about the router: It's a normal ADSL/VDSL router which sends WiFi signals. Distributed by the market leader ISP in my country. It also can do WPS. Here's a link: https://www.swisscom.ch/en/residential/help/device/internet-router/centro-grande.html

Update: I came to the conclusion that it's absolutely not possible to find the router, even though I didn't try the kids trick yet, as raystafarian says, you should only use previously known children and I don't know that many children ;-). The woman who cleans the house said she never saw anything like a router there and the Wifi Analyzer App told me it's most likely inside the wall. Nevertheless it's a great tool and I will accept it as an answer. We're now installing a new router and if, one day, we're able to find the mysterious router location, I'll let you guys know. Cheers!


Source: (StackOverflow)

Is there a cap on simultaneously active Wi-Fi Access points in a single area?

I'm writing an API for controlling an external device. Part of this API is having the device scan for Wi-Fi access points. The API will be implemented across many types of devices, with varying memory capacity. I want to know whether I can just allocate a buffer for found access points once and then forget about it, or whether I need to handle this via dynamic memory allocation.

To make that decision, I need to know how many different Wi-Fi networks/access points can be available in a given area.

At work, when I do a Wi-Fi scan, I pick up 16 different Wi-Fi networks. Even if most of these Wi-Fi networks are poorly reachable, I still wish to pick them up with my Wi-Fi scan.

Is there a cap on simultaneously active Wi-Fi Access points in a single area? More specifically, is there a cap on simultaneously active Wi-Fi networks in a single area? If so, what happens if you go over it?


What I tried (Research)
I tried googling, but the only thing that seems to come up is a limit on the amount of devices per access point. Various searches ("access point limit", "wifi max access point") didn't give me the result I was looking for.

I then tried with different search terms, trying to find out how Wi-Fi scans work. I found out that they work via sending a packet that basically says hello, and then listening for how many hellos they get back.
This seems to indicate to me that there is no cap; I could, in theory, buy many power strips, plug a lot of Wi-Fi access points in (perhaps all connected to one big router so they're connected to the internet, perhaps not), do a Wi-Fi scan and find many access points, provided they have different SSID's. (I don't plan on doing this; even if I did, there'd be no way to know if I'm being limited by the protocol or by the scanner.)
Is this correct? Is there no cap on Wi-Fi access points? Would said theoretical scenario even work in practice?


Source: (StackOverflow)

How much Wi-Fi signal strength do I lose per foot of antenna cable?

I'm thinking of buying an antenna for a router so I can extend my Wi-Fi. I have seen a few products like TP-Link TL-ANT2405C Indoor Desktop Omni-directional Antenna:

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The length of the wire is 130 cm. Is it OK if I increase the length of the wire or will it affect the performance of the router? What is the maximum cm of length that I can increase?


Source: (StackOverflow)

Can I make two wireless routers communicate using the wireless?

I want to make a setup like this:

cable modem <-cable-> wireless router 1 <-wireless-> wireless router 2 in another room <-cables-> PCs in another room

Basically, I want to extend my network access across the house and then have a bunch of network jacks available for my office PCs.

Right now, I have a cable modem going to a wireless router in one room and a PC with a wireless PCI card in it in the office on the other side of the house. I use internet connection sharing with the other PCs in the office. The problem is that ICS is flaky, especially when I switch to VPN on the Windows box to access files at work. I picked up a wireless USB adapter that I thought I could share among the PCs I work on but I'm not very happy with it so I'm going to return it (NDISwrapper support for it is poor).

Is this possible? My wireless experience so far has been pretty straightforward so I have no idea what kind of hardware is available. I've looked at network extenders but those just look like repeaters for signal strength. I want wired network jacks in my office.


Source: (StackOverflow)

How do I diagnose and visualize high ping times to wifi router?

I'm seeing erratic and sometimes very long ping times to my wifi router that's just one hop away. Pinging 192.168.1.1 sometimes gives stretches of 400-800ms latencies.

There are plenty of things to try (firmware, router placement, AP channel, etc.), but I would like to attack this problem a bit more methodically:

  • First, how can I visualize the performance of my network?
  • Then, how can I benchmark the performance of a given configuration, so that I can compare reliably after making adjustments?

Source: (StackOverflow)

How to launch a command on network connection/disconnection?

I have a wifi connection that requires to authenticate using a web form once the wireless link is established. I know how to automate the authentication with a script that uses curl/curlIE.

But how can I ask Windows to call my script every time I connect to a particular network connection?

I would be also interested in receiving the name of the wireless profile or the ESSID on the command-line of my script.


Source: (StackOverflow)

How can I get the same SSID for multiple access points?

I need to upgrade my existing wireless infrastructure and this time I want 2 access points to cover my house, since I get blind spots no matter what with a single AP. I have physical cabling to my central network available for both access points.

I would really like these two to interoperate seamlessly as a single SSID. How do I do this? What are the features that the new access points I'm buying would need to support?


Source: (StackOverflow)

Which routers do you prefer for DD-WRT or OpenWRT? [closed]

I'm aware of the giant Supported Devices list. I'm wondering which ones you all prefer (e.g., support for Mega install, cheap, reliable hardware, USB port, etc.)

I've used an ASUS WL-500G Premium for 1.5 years, but I've been eyeballing the WL-520gU recently.


Source: (StackOverflow)

How do I set my wireless network to be private instead of public?

Trying to maintain good security settings on my laptop, I want my home network to be interpreted as private and the university network at school to be interpreted as public. However, my home network is currently showing as public.

Here is what my Network and Sharing Center looks like:

How do I change my home network from public to private on Windows 8 Consumer Preview?


Source: (StackOverflow)

What does the "Fi" in "Wi-Fi" mean?

I just got into a heated discussion about Wi-Fi. What does the Fi in Wi-Fi mean? I would have thought potentially "frequency interface" since all network adapters are classified as interfaces. However I'm not certain.


Source: (StackOverflow)

Display list of computers on a LAN in Linux

I'm a web dev who is trying to get a better handle on security. I'm trying to figure out a way (on Linux/Debian based distros) to list all computers on the same LAN my netbook is on. I tried "arp -n" but I don't feel it's a complete list, as my iPhone is on the same wi-fi router as my netbook, and that didn't come up. Is there some better way to get a full list of machines that are all sharing the same gateway?


Source: (StackOverflow)

How does Google Chromecast connect to secured wifi?

Google Chromecast can be set up by going to the setup page on a supported device. But in technical terms, what is actually happening on your device that configures the Chromecast dongle? For instance, if I have a WPA secured wireless AP, how does the dongle "listen" for configuration information?

afaik the only automatic way of doing this is Wi-Fi Protected Setup (WPS). However, that wouldn't require an additional device. So it seems like Google is doing something else.


Source: (StackOverflow)

How can I protect myself while using public wifi hotspots?

I frequently need to access secure resources (gmail, banking, remote desktop, etc) while on public wifi hotspots. What can I do to ensure that nobody can sniff my passwords or my other browsing activity?


Source: (StackOverflow)

What is the difference between 2.4GHz and 5GHz wireless?

I just got a new "dual band" wireless router. The sales rep didn't really understand the difference between the "2.4GHz" and "5GHz" wireless networks that the router supports.

Can anyone please explain the difference to me?


Source: (StackOverflow)

How to put fear of God (law) into Wi-Fi hacking neighbors [closed]

I live in an apartment and some new guys have apparently moved into one of the apartments. They have been shamelessly hacking into my WiFi.
Mine was initially a WEP encrypted network and out of laziness I just limited and reserved the IPS on my router for the people in my house.
Yesterday I had to free up an IP for a guest in my house but before he could join the network these guys connected in.
I have changed my encryption to WPA2 and hope they dont have the hardware/patience required to hack into it, but there are many wi-fi networks in my apartment most of which are secured using WEP. I don't really want to call the police on them. Is there any way to deter them from misusing other people's wi-fi ?

I have gone through I think someone else has access to my wireless network. What next? but I have already taken the steps mentioned there.


Source: (StackOverflow)