Wireless LAN 802.11 Service Sets

Hello Michael

Actually, it doesn’t send it out at the same time. If the AP has only a single radio, it will only function in half-duplex. It must, therefore, share access to that radio for connectivity to all user devices and to the AP that connects it to the rest of the network. This is done using the normal CSMA/CA method.

Although this is the case, it would be best practice to ensure that your repeater has at least two radios, and have one radio be exclusively used for connectivity to the AP. You can also configure the link between the repeater and the AP to function on a different channel to that providing access to the user devices, allowing that link to be free from interference from the end devices.

I hope this has been helpful!

Laz

Hi Laz and Rene,

Is there any lesson about dhcp & dhcp relay using wireless devices , also some basic operation of AP’s and the connectivity protocols messages and operation? (Like beacon and probes as mentioned in your “introduction to wireless network” lesson regarding hiding the SSID?)

Also, I want to make sure that the repeater isn’t the only option available for extending the range of the RF signal, after all we can use the MBSS topology for that, am I right?

Hello Nitay

For the time being, the only content for wireless is what you see in the CCNA course (Unit 3.4) and the ENCOR course (Unit 3).

If you have suggestions for expanding this content, please feel free to go to the Member Ideas page and make your suggestions. You may find that others have also made these suggestions, to which you can add your voice.

Yes, the MBSS topology is indeed a different from a repeater, however, the concept is the same. The MBSS can be considered a glorified repeater in that it wirelessly extends the coverage area, but has additional intelligence that allows the wirelessly meshed devices to reroute traffic between APs, essentially “healing” the topology if a failure takes place. A repeater cannot do this.

Ideally, a wired access point with the same SSID is the best way to extend the range of an SSID to create an ESS. However this is not always possible, so one way is using a repeater, the other an MBSS, and a third option is using a point to point connection, using two additional access points, to essentially create a wireless bridge to which the remote access points connects. This extends the network wirelessly to the remote access point, but from the point of view of the access point, it looks like a direct wired connection.

I hope this has been helpful!

Laz

Hi all,

Just a question on the trunking section.

If I have multiple VLANs trunked on the switchport that connects to the AP such as 10 and 20 for two different subnets, what would I use a native VLAN for?

I’ve been told that it’s needed, and I can only imagine for AP management perhaps? Does the AP not tag any packets that’s sent directly from itself rather than VLANs hence having the switch to tag it for the AP?

Sorry if that’s badly worded. I just need to know why I’d need a native VLAN for the trunk port.

Hello Calum

The native VLAN is a configuration component of a trunk regardless of what device it is connected to, either an AP, or another switch. By default, the native VLAN will be 1, but best practice dictates that you should change it to another value. All of this is detailed in the following lesson.

To find out more about what the native VLAN is used for and how it operates, take a look at the following NetworkLessons note:
https://notes.networklessons.com/native-vlans-and-untagged-frames

Now specifically for an access point, the native VLAN plays an additional role. If you are using a repeater, then you must make sure that the SSID on the root AP and the same SSID on the repeater AP use the native VLAN. More information on this detail can be found at the following Cisco documentation:

I hope this has been helpful!

Laz

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Thanks for the detailed response Laz!

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Hi Rene/Laz,
How many percent is the recommended overlap between the channels in the image below?

Hello Ferdinand

It is important to note that the coverage area of an access point never has a distinct boundary, as shown in the circles in the diagram. It looks more like a fuzzy boundary than a line. In real life, you will find that it is even more difficult to define that boundary, because of obstacles, interference, and real signal distribution patterns. So to give an exact percentage of overlap as a best practice is very difficult to do.

As a general guideline, if an access point has a range of, say, 50 meters in a given environment, two access points should be placed at a distance of around 90 meters, in order to have an overlap of about 10 meters.

In reality, however, there are so many variables involved that you almost never use this specific guideline. In most cases, such coverages are determined experientially rather than theoretically. In a more dense user environment, you will have much more overlap to accommodate a higher number of users.

Performing a site survey will also give you more insight into how wireless signals will propagate, and what kind of ranges you can expect given the environmental obstacles on a case by case basis.

I hope this has been helpful!

Laz

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In a large Enterprise floor which needs roaming, can we connect have two different access points from 2 different vendors, will that work?

Hello Akila

There are several definitions of roaming, so it really depends upon what we mean when we use this term. For details about those definitions, take a look at this NetworkLessons Note on Wireless Roaming.

You can achieve roaming with APs of different vendors if you have the same SSID configured on both APs, and the client moves from one coverage area to the next. The client will disassociate from one AP and associate to the next, resulting in a short disconnection. However, this is not the strict definition of roaming.

Roaming with its strict definition means a client may roam from one AP to the next without a disassociation, and therefore without any disconnection. Such roaming for Wi-Fi is defined by the IEEE 802.11r standard, therefore it can theoretically be implemented by multiple vendors. However, because this standard requires coordination with a particular wireless controller, it is impractical to attempt to achieve it using APs from different vendors. So I would say this kind of roaming is difficult (but possibly not impossible) to achieve between vendors.

I hope this has been helpful!

Laz

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I have a Question Mr. Rene. (I could not find the question field that is why I am using this reply field to ask the question). In your description about ESS, you defined BSS1 and BSS2 in the image. It should be ESS1 and ESS2 right? Also you said there would be seamless roaming in ESS (but WLC was not connected in the image to provide a seamless roaming). Is it possible to do seamless roaming just by connecting 2 APs to a switch? It will cause an interuption prior connecting to the second AP right? Also instead the BSSID, it should be ESSID right?

Hello Peter

First of all, you’re asking your question in the right place. The forum is where you can freely post your queries so that we can respond to them here.

As far as terminology goes, a BSS is defined as the coverage delivered by a single physical access point. The BSS has a unique BSSID which is the MAC address of the device, but can have a configurable SSID.

An ESS is defined as the collective coverage delivered by multiple physical access points that have the same SSID. Thus, by definition, an ESS is composed of multiple BSSes with the same SSID but unique BSSIDs. Therefore, the labeling in the diagram is correct. Does that make sense?

As far as “seamless” roaming, what it actually means depends upon the context and the definition of the concept. You are correct that by simply creating the same SSIDs in different BSSes, it will not necessary provide you with roaming without any disruptions. Take a look at this NetworkLessons Note on Wireless Roaming Defined that tells us a little bit more about what “seamless roaming” really means.

I hope this has been helpful!

Laz

I noticed there are, at least, 2 different modes, non-infrasctructure and the other is infrasctructure (?) . Non-infra could be repeater, Workgroup Bridge and Outdoor bridge and Infra is a mode that you could change by software ? for example, the several modes that support Cisco APs such as Flexconnect, SE-Connect, Monitor, etc

Wireless is one of my weakest topics , i’d like to dive more in wireless but specific to outdoor such as outdoor bridge to give internet service using Radio Link as last mile. Do you recommend any book about that ?

Hello Juan

The terminology used can be confusing. Let me try to clarify.

When it comes to Wi-Fi, there are two implementation modes: Infrastructure mode and ad hoc mode (also called IBSS).

Infrastructure mode uses an AP as a central “hub” to which clients connect. Via that AP they connect to other clients or to other networks, or to the Internet. Infrastructure mode is characterized by the fact that there is dedicated hardware specifically used to connect the client to the “infrastructure.” That hardware is essentially an AP and any other wired or wireless infrastructure used to connect to other networks.

Ad Hoc mode or IBSS mode is used to connect wireless clients directly to each other. Here there is no infrastructure involved. There is just direct one-to-one communication.

Now when it comes to Cisco APs, you can configure them using several Access Point modes (AP modes). This is different than the infrastructure/ad hoc modes mentioned before.

AP modes essentially tell the access point how to operate. These are described in detail in the lesson. Since an AP is being used, all of these involve infrastructure mode.

Concerning the implementation of wireless links for last-mile communication, I don’t have any books to recommend, but there are many resources online for such wireless links, especially from vendors that are well-known for such equipment. They have huge knowledge bases and how-to sections in their online resources that are freely available. I can’t share the names of those vendors here but I’m sure you have some in mind.

I hope this has been helpful!

Laz

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Hello,

Out of curiosity I was thinking about a scenario where the end user hosts would be ARPing for each other’s MAC addresses in an enterprise environment, and the only example I could think of was an ad hoc network. Are there any other ones?

Attila

Hello Attila

An ARP request is sent whenever a host needs to discover the MAC address of the next hop, or the destination host in the event the host is in the same subnet.

Now if you have two devices connected to a Wi-Fi network, to the same SSID and the same VLAN, and those devices are on the same subnet, then any communication that is to take place between these two particular wireless clients will require an ARP request.

ARP functions exactly the same way on wireless networks as on wired networks. Imagine that those two same hosts are connected to a switch on the same VLAN via UTP cables. Again, if one host wants to communicate with the other, an ARP request will necessarily be sent.

What applications require this direct client-to-client communication that in turn requires the use of ARP for those devices to communicate? Well, there are several including things like gaming, VoIP, collaboration tools, and even printing to a network printer.

For one wireless client to ask for the MAC address of another wireless client directly using ARP, they both must be on the same subnet.

I hope this has been helpful!

Laz

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I created a lab with two (2) ap. so I had a essid, both AP had same ssid and sam passphrase for wpa2. Roaming did work, sometimes well sometimes not so good. Each AP was a different vendor (cisco AP and sagecom AP from spectrumISP). When the clients leave one ap and come back, are they reassociating or are they simply associating again? I will try wireless debug on the cisco AP and see if I can figure it out.
thanks!

Hello @rod.deluhery ,

Debugging this is a good idea. It’s hard to tell how it works exactly because different vendor APs support different standards. For example, here are some of the standards related to roaming:

  • 802.1F
  • 802.11k
  • 802.11r
  • 802.11v

I would enable a debug on both the Cisco AP and your sagecom AP, then roam and see what happens :slight_smile:

Rene

What exactly is the difference between using a repeater with multiple radios (one receives AP signal and other transmits to end devices) and a Mesh AP? It sounds like they are doing the exact same thing: one radio connects to an AP wirelessly and another radio connects to the end device: the latter picks up the client traffic and the former forwards it to the AP/Root AP.

Hello CJ

Indeed a repeater with multiple radios sounds very similar to a mesh network. Although the mechanism through which they operate is similar, there are some significant differences.

The difference between using a repeater with multiple radios and a Mesh Access Point (AP) lies in their design, functionality, and network architecture. First of all, keep in mind that “mesh” is actually an infrastructure mode while the repeater is an AP mode. The former has to do with larger scale wireless network design while the latter has to do with the mode of a particular device. Although they are similar in operation, the scope of their implementation is different.

A repeater with multiple radios uses one radio to receive the signal from the main AP, and the other to transmit the signal to end devices. This design is a step up from using a single-radio where the same radio has to alternately receive and transmit signals, effectively halving the bandwidth. However, this is still a relatively simple setup aimed only at extending the range of an existing network.

A mesh AP is part of a more sophisticated mesh system. These APs are designed to dynamically communicate with each other and with the main network, creating a mesh-like interconnectivity. Each mesh AP can act as a router, forwarding data to other mesh APs and end devices. They are typically more intelligent in managing network resources, and routing, and can provide better coverage and reliability compared to simple repeaters.

While both systems aim to extend wireless coverage, mesh APs are part of a more advanced, scalable, and efficient network architecture compared to repeaters with multiple radios, which are more suited for simpler, small-scale range extension.

I hope this has been helpful!

Laz