WIRELESS AND VIRTUAL LAN

Wireless LAN

WLAN is the holy grail of wireless networking for most of the business world.

Using the IEEE 802.11 standard, it is the main topic for most of this book.

Wireless Local Area Networking (WLAN) gets you connected to the office with

your laptop or tablet PC, allowing you to roam around at work while remaining

connected.

This is where Wi-Fi — a term sometimes used interchangeably for the IEEE

802.11 standard — originates. This wireless connectivity expands beyond

the area of our desks and moves us to further distances. Distances of up to

500 feet are possible with no interference, and even farther distances can be

easily achieved using repeaters and additional access points.

Using a wireless network takes a number of components and some fairly

critical thinking up front before allowing anyone to connect. We discuss

these components in the next few sections.

Accessing networks

You need tools to access a wireless network. You also need to be aware of the distances and transmission speeds you want to use in order to choose the

correct technology. To quickly summarize, there are a number of competing

wireless standards to consider. Table 1-2 covers the more popular ones.

 

                         Popular Wireless Standards

 

Standard                     What It Means

 

802.11a           54 Mbps speed in the 5 GHz band.

802.11b           11 Mbps transmission in the 2.4 GHz band.

802.11g           54 Mbps; remains backward-compatible with 802.11b.

802.15             Personal Area Network standard. Bluetooth is the typical

name.

network card must support that standard, along with, of course, your wireless

access point. After you add a wireless network card to your machine or PDA,

you are off to the races and can enjoy mobility while remaining connected to

            your network.

Virtual LAN

Virtual LANs have been made possible as the switching infrastructure has replaced the traditional shared media LANs. An individual switch port can be assigned to a logical LAN, the next switch port can be easily assigned to a completely different logical LAN. This is made possible by 'tagging' the frames entering the port so that these frames are identified as belonging to a particular logical LAN whilst they travel along the switch fabric of the box. Once these frames are sent out of their logical LAN ports, the tag is removed from the frame. In the past, proprietary frame tagging has been implemented by Cisco (Inter Switch Link or ISL) and Bay Networks (Lattis Span), but the standard is now defined by 802.1q and may be the one that you go for in order to allow interoperability between different manufacturers boxes.

VLANs allow you to connect any user to any logical LAN. The benefit here is that the user could be anywhere in the building or even another building. A particular department does not have to have all its employees physically situated in the same place. In addition, security is easily maintained since the only way to communicate between the virtual LANs is by routing between them, either by way of a router (slow) or via a layer 3 switch.

Originally, VLANs were simply based on port ID i.e. different ports being assigned to different VLANs. This is fine if the different groups are local, but not flexible enough to accommodate campus-wide VLANs. 'Port-centric' VLANs require no lookup table and are easy on the processor especially if an ASIC is taking care of the switching, plus there is a high level of security as packets are very unlikely to 'leak' into other VLANs. These type of VLANs are often referred to as Static VLANs as they are manually configured.

Frame filtering is often used by switches to aid in minimising LAN traffic. Tables are kept and frames are compared to the table entries to varying levels of frame depth. The deeper into the frame the switch has to go, the greater the switch latency. Also, the larger the table; the more the latency and these tables need to be synchronised with other switches.