SonicPoint VAP Overview

* 
NOTE: Virtual Access Points are supported when using SonicPoint wireless access points along with SonicWALL NSA appliances.
Topics:
•
What Is a Virtual Access Point?
•
What Is an SSID?
•
Wireless Roaming with ESSID
•
What Is a BSSID?
•
Benefits of Using Virtual APs
•
Benefits of Using Virtual APs with VLANs

What Is a Virtual Access Point?

A Virtual Access Point is a multiplexed instantiation of a single physical Access Point (AP) so that it presents itself as multiple discrete Access Points. To wireless LAN clients, each Virtual AP appears to be an independent physical AP, when in actuality there is only a single physical AP.

Before the evolution of the Virtual AP feature support, wireless networks were relegated to a One-to-One relationship between physical Access Points and wireless network security characteristics, such as authentication and encryption. In other words, an Access Point providing WPA-PSK security could not simultaneously offer Open or WPA-EAP connectivity to clients, and if the latter were required, they would had to have been provided by a separate, distinctly configured Access Points. This forced WLAN network administrators to find a solution to scale their existing wireless LAN infrastructure to provide differentiated levels of service.

With the Virtual APs (VAP) feature, multiple VAPs can exist within a single physical AP in compliance with the IEEE 802.11 standard for the media access control (MAC) protocol layer that includes a unique Basic Service Set Identifier (BSSID) and Service Set Identified (SSID). This allows for segmenting wireless network services within a single radio frequency footprint of a single physical access point device.

VAPs allow you to control wireless user access and security settings by setting up multiple custom configurations on a single physical interface. Each of these custom configurations acts as a separate (virtual) access point, and can be grouped and enforced on single or multiple physical SonicPoint access points simultaneously.

Figure 26. Virtual Access Point configuration

For more information on SonicOS Secure Wireless features, refer to the SonicWALL Secure Wireless Integrated Solutions Guide.

What Is an SSID?

A Service Set IDentifier (SSID) is the name assigned to a wireless network. Wireless clients must use this same, case-sensitive SSID to communicate to the SonicPoint. The SSID consists of a text string up to 32 bytes long. Multiple SonicPoints on a network can use the same SSIDs. You can configure up to 8 unique SSIDs on SonicPoints and assign different configuration settings to each SSID.

SonicPoints broadcast a beacon (announcements of availability of a wireless network) for every SSID configured. By default, the SSID is included within the beacon so that wireless clients can see the wireless networks. The option to suppress the SSID within the beacon is provided on a per-SSID (e.g. per-VAP or per-AP) basis to help conceal the presence of a wireless network, while still allowing clients to connect by manually specifying the SSID.

The following settings can be assigned to each VAP:

•
Authentication method
•
VLAN
•
Maximum number of client associations using the SSID
•
SSID Suppression

Wireless Roaming with ESSID

An ESSID (Extended Service Set IDentifier) is a collection of Access Points (or Virtual Access Points) sharing the same SSID. A typical wireless network comprises more than one AP for the purpose of covering geographic areas larger than can be serviced by a single AP. As clients move through the wireless network, the strength of their wireless connection decreases as they move away from one Access Point (AP1) and increases as they move toward another (AP2). Providing AP1 and AP2 are on the same ESSID (for example, ‘sonicwall’) and that the (V)APs share the same SSID and security configurations, the client will be able to roam from one to the other. This roaming process is controlled by the wireless client hardware and driver, so roaming behavior can differ from one client to the next, but it is generally dependent upon the signal strength of each AP within an ESSID.

What Is a BSSID?

A BSSID (Basic Service Set IDentifier) is the wireless equivalent of a MAC (Media Access Control) address, or a unique hardware address of an AP or VAP for the purposes of identification. Continuing the example of the roaming wireless client from the ESSID section above, as the client on the ‘sonicwall’ ESSID moves away from AP1 and toward AP2, the strength of the signal from the former will decrease while the latter increases. The client’s wireless card and driver constantly monitors these levels, differentiating between the (V)APs by their BSSID. When the card/driver’s criteria for roaming are met, the client will detach from the BSSID of AP1 and attach to the BSSID or AP2, all the while remaining connected the SonicWALL ESSID.

Benefits of Using Virtual APs

•
Radio Channel Conservation—Prevents building overlapped infrastructures by allowing a single Physical Access Point to be used for multiple purposes to avoid channel collision problem. Channel conservation. Multiple providers are becoming the norm within public spaces such as airports. Within an airport, it might be necessary to support an FAA network, one or more airline networks, and perhaps one or more Wireless ISPs. However, in the US and Europe, 802.11b networks can only support three usable (non-overlapping) channels, and in France and Japan only one channel is available. Once the channels are utilized by existing APs, additional APs will interfere with each other and reduce performance. By allowing a single network to be used for multiple purposes, Virtual APs conserve channels.
•
Optimize SonicPoint LAN Infrastructure—Share the same SonicPoint LAN infrastructure among multiple providers, rather than building an overlapping infrastructure, to lower down the capital expenditure for installation and maintenance of your WLANs.

Benefits of Using Virtual APs with VLANs

Although the implementation of VAPs does not require the use of VLANs, VLAN use does provide practical traffic differentiation benefits. When not using VLANs, the traffic from each VAP is handled by a common interface on the security appliance. This means that all traffic from each VAP will belong to the same zone and same subnet (Footnote: a future version of SonicOS will allow for traffic from different VAPs to exist on different subnets within the same zone, providing a measure of traffic differentiation even without VLAN tagging). By tagging the traffic from each VAP with a unique VLAN ID, and by creating the corresponding subinterfaces on the security appliance, it is possible to have each VAP occupy a unique subnet, and to assign each subinterface to its own zone.

VAPs afford the following benefits:

•
Each VAP can have its own security services settings (e.g. GAV, IPS, CFS, etc.).
•
Traffic from each VAP can be easily controlled using Access Rules configured from the zone level.
•
Separate Guest Services or Lightweight Hotspot Messaging (LHM) configurations can be applied to each, facilitating the presentation of multiple guest service providers with a common set of SonicPoint hardware.
•
Bandwidth management and other Access Rule-based controls can easily be applied.