Cisco Aironet Access Point Antenna Selection

When deploying any type of wireless network it is critically important to choose the right antennas and proper mounting hardware. I highly recommend reading through the document linked below to become familiar with both wireless technology in general as well as product specific information based on antenna models. Understanding how various antennas operate will also help determine what type of mounting hardware will work the best given a specific scenario.

Cisco Aironet Antenna and Accessories

Remember that no amount of reading or strategizing can replace a good site survey!

Cisco Aironet Wireless Access Point Regulatory Domains

When it comes to ordering wireless access points there are a number of important pieces to consider including regulatory domain, antenna selection, and mounting hardware.

Regulatory domains are simply a way of grouping countries that have common policies related to radio frequency equipment (power level, channel set, etc.). If you’re only installing hardware in a single country then you’ll never need to concern yourself with choosing a different regulatory domain. If, however, your equipment spans several countries you need to evaluate which regulatory domain applies to each country. Here’s a link to Cisco’s Wireless LAN Compliance Status page. This page details which products are licensed for use in a specific country as well as which regulatory domain to use when ordering products.

The regulatory domain used for ordering a Cisco wireless access points is simply referred to by a single letter. When determining the part number to order simply substitute the letter of the regulatory domain with the ‘x’ in the product part number.

For example, to order a 3502 (with integrated antennas) for use in Mexico one would change the generic part number AIR-CAP3502I-x-K9 to AIR-CAP3502I-N-K9

Be aware that the regulatory domain can NOT be changed on an existing access point.

Cisco IOS DHCP inheritance

Until recently I was completely unaware of the fact that DHCP server attributes on Cisco IOS support inheritance which not only shortens configurations, but decreases the chances of making typographical errors. The feature works quite simply. When Cisco IOS receives a DHCPDISCOVER message it matches the request against all matching DHCP pools based on the IP and subnet assigned to the interface that the DHCPDISCOVER message was received on. For example a router with an Ethernet interface configured as follows would look for DHCP scopes matching 192.168.1.0/24:

interface FastEthernet0/1
   ip address 192.168.1.1 255.255.255.0

Basic DHCP pool configuration:

ip dhcp pool DHCP-POOL
   network 192.168.1.0 /24
   default-router 192.168.1.1
   domain-name MyDomain.local
   dns-server 8.8.8.8 4.4.4.2

I would also recommend excluding a portion of any DHCP scope for things that are going to be statically assigned. I will be excluding the following address range for this example 192.168.1.1 -> 192.168.1.10. This can be done using the following syntax:

ip dhcp pool excluded-address 192.168.1.1 192.168.1.10

If I want to extend this configuration and hand out a static DHCP reservation to my laptop should I duplicate all the settings I’ve already defined for the “DHCP-POOL” scope or just the ones that are unique? The answer is you can do either! I would recommend shortening your configuration and specifying only what you need. Here’s an example:

ip dhcp pool MYLAPTOP
   hardware-address 0012.3456.1111
   host 192.168.1.100 mask 255.255.255.0

Notice that the only thing I’m specifying is the hardware-address which matches the MAC address of my laptop and the host attribute which is the static reservation I want to always give to this DHCP client.