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I have a WiFi base station, and a WiFi range extender. Both of them have the same SSID.

When a device connects to that SSID, what exactly happens? How does the device know that base station and range extender are part of the same network and no third party can impersonate another range extender on the same network?

Then, what happens if the device moves around and signal strengths change? Is there some kind of renegotiation going on?

What does the range extender actually do? Simply rebroadcast whatever it gets from device and base station, or is it more intelligent than that?

This sounds like several questions, but if somebody had a concise explanation handy, it would probably answer all of those at the same time.

  • Huh? If was an electrical engineer maybe i would understand all the previous answers. Just tell me, do they really work or not? Yes or No answer. – user24856 Apr 23 '16 at 18:37
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There are two types of wireless extenders. First would be an extender that uses some sort of mesh technology. This type of extender is typically only found within an enterprise deployment and will establish a connection to the network in addition to also acting as an AP. Often a mesh device will use two radios, one providing the "back haul" and one to provide client access.

However most devices referred to as wireless extenders fall into the second group and are actually just repeaters. When a wireless repeater receives (or "hears") a frame, it will then transmit a copy of that frame into the air. Naturally it will only hear frames on the channel to which it is configured, and typically will also be configured to only re-transmit frames for a particular SSID or BSSID.

Since RF is a shared resource, this repetition of data can result in a significant loss of performance. To reduce this impact, some repeaters are smart enough to not repeat frames where it hears both the frame and the acknowledgement between the AP and client device, but others are not and will re-transmit all frames. Even if you are using a "smarter" repeater, if the client is too far from the repeater to be heard, all AP traffic will get repeated leading to the same loss of performance.

When a device connects to that SSID, what exactly happens?

When a client device connects, it goes through an association process with the access point. If the client is out of range of the AP, but within range of the repeater, the repeater will re-transmit the client frames as well as the return frames from the AP.

How does the device know that base station and range extender are part of the same network and no third party can impersonate another range extender on the same network?

The device doesn't. When function as a repeater, the repeater itself doesn't really have any "identity" on the network (any management interface on the repeater is a separate matter). It is merely repeating the frames that it hears unchanged.

Even if a third party does place a repeater on in the area, this is not really a problem as the client device is associating (and establishing encryption) with the access point itself and not the repeater.

Then, what happens if the device moves around and signal strengths change? Is there some kind of renegotiation going on?

With most repeaters, there is no roaming or renegotiation. The client device will either see the frame from the original AP, the repeated frame from the repeater, or possibly both.

What does the range extender actually do? Simply rebroadcast whatever it gets from device and base station, or is it more intelligent than that?

See above.

  • 1
    Interestingly, this answer doesn't cover the behavior I see from my TP-Link TL-WA850RE range extender. When the client device is on the extender, the other devices (at least on the main AP wireless and wired side) have the extender's MAC address associated w/the client's IP in their ARP tables... as if the extender is performing some kind of hybrid layer-2 NAT (!?). This behavior seems to confuse my main AP (cable modem/wireless router, also does DHCP), presumably due to some kind of anti-spoofing that doesn't this migration of an IP address between MACs. – Michael - sqlbot May 28 '15 at 19:40
  • Sounds like this may be behaving like the first type of wireless extender or more like a mesh AP mentioned in the first paragraph? I can't say specifically as I have no experience with this TP-Link product. – YLearn May 28 '15 at 22:59
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Range extenders use WDS (wireless distribution system) to join a wireless network and act as a store & forward repeater to extend radio coverage.

The range extender needs to use the same setting (except for the SSID) as as the AP (channel, encryption method/keys). Some range extenders allow you to enter a different SSID so you know that you are connecting to the range extender instead of the AP.

The device doesn't know that the range extender is part of the same network. A 3rd party can just as easily impersonate the range extender as they can any other wifi AP or client.

Range extenders are soho equipment so they typically don't have the client management features that you'd find in many enterprise/carrier system. This means any handling of roaming would be up to the client device.

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