Route Filters

When creating route patterns, you can use the "@" wildcard to represent all the routes defined in the North American Numbering Plan (NANP). Although this is a simple way to provide PSTN access to your internal users, you might be providing far more access than you intend. As shown in Figure 11-1, the NANP includes high-expense patterns such as international dialing access, service numbers (such as 411), and 900 numbers. You can assign route filters to route patterns with the @ route pattern to help reduce the danger that full access to the NANP provides. You can accomplish this reduction by filtering what is included in the @ (or 9.@) route pattern.

Figure 11-1. @ Route Pattern Without Route Filters

When using the 9.@ route pattern, Cisco CallManager recognizes that dialing is complete when the user dials 1 + 10 digits (signifying long-distance dialing) or just dials 10 digits (local area codes without the 1). If the number dialed does not begin with a 1, Cisco CallManager considers it a local area code and assumes that dialing is complete after 10 digits.

In an area where seven digits are dialed for local numbers, Cisco CallManager cannot recognize which office exchange codes (NXXs) to use for routing unless you specifically code them as route patterns.

Note

NXX is the central office (CO) exchange code, which consists of three digits that designate a particular CO or a block of 10,000 subscriber lines. N is any digit between 2 and 9, and X is any digit between 0 and 9.

Generally, telephone company service providers arrange many NXXs in a given area code contiguously where you can use route pattern wildcards to assist in your configuration. Coding these individual route patterns for NXXs can be extremely difficult. You can use a route filter to simplify this procedure.

A route filter called seven-digit dialing is always preconfigured in Cisco CallManager. You should assign this route filter to any 9.@ route pattern in an area that uses seven-digit dialing. This route filter removes all local area codes. If a dialed number does not begin with a 1, then it is a seven-digit number, and Cisco CallManager considers dialing complete after seven digits. This situation requires you to configure local area codes specifically as separate route patterns. Doing so is generally not an issue because the number of area codes in a geographical region is usually small.

Note

Route filters are only used with the @ route pattern and are not necessary if you have configured a robust dial plan (that does not use the @ route pattern).

Route Filter Tags

You can design and configure route filters using a number of predefined tags in the Cisco CallManager CCMAdmin web utility. Table 11-1 provides a list of tags available to you when implementing route filters.

Configuring Route Filters

Route filter configuration occurs in two major steps:

Just as with access lists on routers, you can create route filters all day and they will never make any difference until you have applied them. Just like an access list, the sole purpose of a route filter is to match criteria; how you apply the route filter determines if the criteria is permitted or denied.

To configure a route filter, use the Cisco CallManager Administration window:

After you have accomplished these initial steps, the Route Filter Clause Configuration window appears, as shown in Figure 11-2.

Figure 11-2. Route Filter Clause Configuration Window

From this point, you can combine your tags with operators to define match conditions. Table 11-2 describes the four operators available when configuring route filters.

The following are examples of match conditions using route filter tags and operators:

• A route filter that uses the tag AREA-CODE and the operator DOES-NOT-EXIST selects all dialed digit strings that do not include an area code.
• A route filter that uses the tag AREA-CODE, the operator = =, and the entry 515 selects all dialed digit strings that include the 515 area code.
• A route filter that uses the tag AREA-CODE, the operator = =, and the entry 5[2-9]X selects all dialed digit strings that include area codes in the range of 520 through 599.
• A route filter that uses the tag TRANSIT-NETWORK, the operator ==, and the entry 0288, along with the tag TRANSIT-NETWORK-ESCAPE, the operator ==, and the entry 101, selects all dialed digit strings with the carrier access code 1010288.

Applying Route Filters

After you have configured the route filter, you must apply them to a route pattern or translation pattern to define the permit or deny action.

Note

Translation patterns are discussed later in this chapter.

To apply the route filter you have created to a route pattern, perform the following steps:

Practical Route Filter Example

To demonstrate route filter configuration, imagine that a company wanted to create a route filter that kept 1-900 numbers from being made available in the CallManager route plan. The first step would be to create a route filter that matched the area code 900, as shown in Figure 11-4.

Figure 11-4. Route Filter Matching the 900 Area Code

After the route filter has been added to the configuration, you then need to apply it to a route pattern to define the action required. Figure 11-5 illustrates the creation of a 9.@ route pattern (representing the NANP) with the Match 900 Numbers route filter applied. The key action rests in the Route This Pattern or Block This Pattern radio buttons. If you select to Route This Pattern, you would add only 900 numbers to the Cisco CallManager route plan. Unless you had a very strange organization, this is not a desired effect. Rather, you would select the Block This Pattern radio button to block any numbers containing the 900 area code.

Figure 11-5. Route Pattern Configuration

CallManager allows you to configure multiple 9.@ route patterns, provided each has a unique route filter configuration. This provides flexibility when creating your route plan. By combining multiple 9.@ route patterns with unique route filters, you can route (or block) exactly what you want from the CallManager route plan.

Tip

You could also accomplish this same objective by creating a route pattern of 1900XXXXXXX and choosing Block this Pattern under the route pattern configuration.