Table Of Contents
Configuring Port to Application Mapping
This chapter describes the Cisco IOS Firewall Port to Application Mapping (PAM) feature. PAM enables CBAC-supported applications to be run on nonstandard ports. Using PAM, network administrators can customize access control for specific applications and services to meet the distinct needs of their networks.
For a complete description of the PAM commands in this chapter, refer to the chapter "Port to Application Mapping Commands" of the Cisco IOS Security Command Reference. To locate documentation of other commands that appear in this chapter, use the command reference master index or search online.
To identify the hardware platform or software image information associated with a feature, use the Feature Navigator on Cisco.com to search for information about the feature or refer to the software release notes for a specific release. For more information, see the "Identifying Supported Platforms" section in the chapter "Using Cisco IOS Software."
Information About Port to Application Mapping
Port to Application Mapping (PAM) is a feature of the Cisco IOS Firewall feature set. PAM allows you to customize TCP or UDP port numbers for network services or applications. PAM uses this information to support network environments that run services using ports that are different from the registered or well-known ports associated with an application.
Using the port information, PAM establishes a table of default port-to-application mapping information at the firewall. The information in the PAM table enables Context-based Access Control (CBAC) supported services to run on nonstandard ports. Previously, CBAC was limited to inspecting traffic using only the well-known or registered ports associated with an application. Now, PAM allows network administrators to customize network access control for specific applications and services.
PAM also supports host or subnet specific port mapping, which allows you to apply PAM to a single host or subnet using standard access control lists (ACLs). Host or subnet specific port mapping is done using standard ACLs.
This section contains the following sections:
How PAM Works
PAM generates a table of information that identifies specific applications with specific TCP or UDP port information. When the firewall router first starts up, the PAM table is populated with system-defined mapping information. As you customize the mapping information, the PAM table is modified with the new information. The information in the PAM table serves as the default port mapping for traffic passing through the firewall.
PAM works with CBAC to identify the applications associated with various port numbers, including services running on non-standard ports, as it inspect traffic passing through the firewall. Previously, CBAC was limited to inspecting traffic using only the well-known or registered ports associated with an application.
Entries in the PAM table provide three types of mapping information:
System-Defined Port Mapping
PAM creates a table, or database, of system-defined mapping entries using the well-known or registered port mapping information set up during the system start-up. The system-defined entries comprise all the services supported by CBAC, which requires the system-defined mapping information to function properly. The system-defined mapping information cannot be deleted or changed; that is, you cannot map HTTP services to port 21 (FTP) or FTP services to port 80 (HTTP).
Note You can override the system-defined entries for specific hosts using the PAM host-specific option. Refer to the section "Host-Specific Port Mapping" in this chapter.
Table 42 lists the default system-defined services and applications in the PAM table.
This section has the following sections:
User-Defined Port Mapping
Network services or applications that use non-standard ports require user-defined entries in the PAM table. For example, your network might run HTTP services on the non-standard port 8000 instead of on the system-defined default port (port 80). In this case, you can use PAM to map port 8000 with HTTP services. If HTTP services run on other ports, use PAM to create additional port mapping entries. After you define a port mapping, you can overwrite that entry at a later time by simply mapping that specific port with a different application.
Note If you try to map an application to a system-defined port, a message appears that warns you of a mapping conflict.
User-defined port mapping information can also specify a range of ports for an application by establishing a separate entry in the PAM table for each port number in the range.
User-defined entries are saved with the default mapping information when you save the router configuration.
Host-Specific Port Mapping
User-defined entries in the mapping table can include host-specific mapping information, which establishes port mapping information for specific hosts or subnets. In some environments, it might be necessary to override the default port mapping information for a specific host or subnet.
With host-specific port mapping, you can use the same port number for different services on different hosts. This means that you can map port 8000 with HTTP services for one host, while mapping port 8000 with Telnet services for another host.
Host-specific port mapping also allows you to apply PAM to a specific subnet when that subnet runs a service that uses a port number that is different from the port number defined in the default mapping information. For example, hosts on subnet 192.168.21.0 might run HTTP services on non-standard port 8000, while other traffic through the firewall uses the default port for HTTP services, which is port 80.
Host-specific port mapping allows you to override a system-defined entry in the PAM table. For example, if CBAC finds an entry in the PAM table that maps port 25 (the system-defined port for SMTP) with HTTP for a specific host, CBAC identifies port 25 as HTTP protocol traffic on that host.
Note If the host-specific port mapping information is the same as an existing system-defined or user-defined default entries, host-specific port changes have no effect.
PAM and CBAC
CBAC uses the information in the PAM table to identify a service or application from traffic flowing through the firewall. With PAM, CBAC can associate non-standard port numbers with specific protocols. For example, if you use PAM to map port 8000 with HTTP services, CBAC can determine that traffic using port 8000 is an HTTP application.
When to Use PAM
Here are a few examples of when you might want to use PAM:
•Use PAM to apply a non-standard port numbers for a service or application.
•Use PAM when a specific host or subnet uses a port number for an application that is different than the default port number established in the PAM table.
•Use PAM when different hosts use the same port number for different applications.
How to Configure Port to Application Mapping
•Configuring Standard ACLs (Optional)
•Configuring PAM (Required)
•Verifying PAM (Optional)
•Monitoring and Maintaining PAM (Optional)
Configuring Standard ACLs
If you require PAM for a specific host or subnet, use the access-list (standard) command in global configuration mode to define an ACL:
Router(config)# access-list access-list-number permit source [source-wildcard]
(Optional) Creates a standard ACL that defines the specific host or subnet for host-specific PAM.
To configure PAM, use the ip port-map command in global configuration mode:
To verify the port mapping information, enter the show ip port-map command in privileged EXEC mode and review the entries:Router# show ip port-map
This command displays all entries in the PAM table, including the system-defined entries.
For PAM configuration examples using the commands in this chapter, refer to the "Configuration Examples for Port to Application Mapping" section at the end of this chapter.
Monitoring and Maintaining PAM
The following commands can be used to monitor and maintain PAM:
Configuration Examples for Port to Application Mapping
Example: Mapping an Application to a Non-Standard Port
In this example, non-standard port 8000 is established as the user-defined default port mapping for HTTP services:ip port-map http port 8000
Example: Mapping an Application with a Port Range
The following PAM entries establish a range of non-standard ports for HTTP services:ip port-map http 8001ip port-map http 8002ip port-map http 8003ip port-map http 8004
Example: Invalid Port Mapping Entry
This example is not valid because it tries to establish port 21, which is the system-defined default port for FTP, as the user-defined port for HTTP services:ip port-map http port 21
Example: Mapping an Application to a Port for a Specific Host
In this example, a specific host uses port 8000 for FTP services. ACL 10 identifies the server address (192.168.32.43), while port 8000 is mapped with FTP services.access-list 10 permit 192.168.32.43ip port-map ftp port 8000 list 10
Example: Mapping an Application to a Port for a Subnet
In this example, a specific subnet runs HTTP services on port 8080. ACL 50 identifies the subnet, while port 8080 is mapped with HTTP services.access-list 50 permit 192.168.92.0 0.0.0.255ip port-map http 8080 list 50
Example: Overriding a System-Defined Port Mapping
In this example, a specific host runs HTTP services on port 25, which is the system-defined port number for SMTP services. This requires a host-specific PAM entry that overrides the system-defined default port mapping for HTTP, which is port 80. ACL 15 identifies the host address (192.168.33.33), while port 25 is mapped with HTTP services.access-list 15 permit 192.168.33.33ip port-map http port 25 list 15
Example: Mapping Different Applications to the Same Port
In this example, the same port number is required by different services running on different hosts. Port 8000 is required for HTTP services for host 192.168.3.4, while port 8000 is also required for FTP services for host 192.168.5.6. ACL 10 and ACL 20 identify the specific hosts, while the PAM entries map the ports with the services for each ACL.access-list 10 permit 192.168.3.4access-list 20 permit 192.168.5.6ip port-map http port 8000 list 10ip port-map http ftp 8000 list 20
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