A company will often have two offices separated by an area through which you simply cannot run connecting cabling. For example, at my company, we leased two buildings across the street from each other. Even if we could obtain right of way to run cabling under the street, the investment would be uneconomic for a leased property.
Options for connecting any two buildings with a network link include:
- Direct-connect private cabling -- fiber or copper
- Leased line from telco
- Wireless technology -- 802.11, microwave, cellular or satellite
Let's say that, as in the example above, we have two leased locations separated by a city street. Assuming that you can deal with any interference and can get a strong signal using some combination of amplifiers and antennas, 802.11 is an excellent choice. Other wireless choices are too complex or expensive. The leased line from the telco might work fine but would have limited bandwidth and an infinite monthly recurring cost. The direct-connect cabling would be the most reliable, but the cost to run fiber under a city street could be tens of thousands of dollars.
Pros and cons of point-to-point wireless networking
Now let's look at the pros and cons of using 802.11 point-to-point wireless networking.
11-54 Mbps, or more, is enough to run most network applications.
Wireless can be prone to interference and reliability problems. For that reason, you need to be prepared to troubleshoot it, and you need to make sure you have enterprise-grade equipment that offers good troubleshooting features. (Don't use wireless bridges from your local electronics store to do this for your business!)
Besides the cost of the wireless gear and implementation, the recurring costs are zero.
|Must have wireless expertise:|
You must have (or hire) the wireless expertise involved to do a site survey and properly install the wireless equipment. This can be most difficult to find at a regular network cabling company. And don't trust your normal cabling company to install wireless until you ensure they have the expertise needed to do it right. Installing wireless bridges incorrectly can result in months or years spent troubleshooting that wireless network.
If you have leased offices, the wireless equipment can easily be moved when you leave -- in contrast to wired cabling.
Sample point-to-point wireless network
Here is a diagram of a sample point-to-point wireless network. This is the network that our configuration will be based on. As you can see, we have two buildings connected by a wireless link.
To do this, we used two Cisco 1310 wireless bridges. Here is the show version of one of these:
Now that you know the exact hardware being used, let's learn about the configurations on these wireless devices.
Configuring the Cisco wireless bridges for point-to-point networking
I have the exact configurations for both of these wireless bridges for you to learn from and use on your own network.
As these are working configurations, a number of configured statements are necessary for things beyond point-to-point bridging. Let's take a look at exactly which statements make the point-to-point bridging that connects these two buildings work.
Configuring the authentication and encryption
The authentication and encryption for the wireless connection are configured when you configure the SSID. In our case, we called our SSID "SEARCHNET." As you can see, we are using WPA authentication with a pre-shared key that will be configured on both bridges.
dot11 ssid [SEARCHNET] authentication open authentication key-management wpa wpa-psk ascii
Configuring the wireless radio
The wireless radio is the interface that connects to the wireless network. It doesn't need an IP address because it is part of the BVI bridge-group. It does need a reference to the SSID, configured above, as that is where the authentication is configured. Notice the encryption mode on the radio. All traffic will be encrypted going across this wireless link.
interface Dot11Radio0 no ip address encryption mode ciphers tkip ssid [SEARCHNET] speed basic-1.0 basic-2.0 basic-5.5 6.0 9.0 basic-11.0 12.0 18.0 24.0 36.0 48.0 54.0 station-role root bridge cca 75 concatenation distance 1 bridge-group 1 bridge-group 1 spanning-disabled
IP address for the BVI
Your wireless bridge must have an IP address and, in this case, this is where you put it: on the bridge virtual interface (BVI).
interface BVI1 ip address 10.99.103.150 255.255.255.0 no ip route-cache
For more information on configuring Cisco 1300 series wireless bridges, see the Cisco documentation.
About the author:
David Davis (CCIE #9369, CWNA, MCSE, CISSP, Linux+, CEH) has been in the IT industry for 15 years. Currently, he manages a group of systems/network administrators for a privately owned retail company and authors IT-related material in his spare time. He has written more than 100 articles, eight practice tests and four video courses and has co-authored one book. His Web site is HappyRouter.com.
This was first published in May 2007