With the new modular policy framework (MPF) introduced in ASA versions 7.x and 8.x, the firewall administrator is now able to apply policing and rate limiting to traffic passing through the ASA appliance. I got a few questions from people how this functionality works and decided to throw in a quick example below which you can easily modify accordingly to match your needs.

Scenario:

We want to rate limit a local internal host when accessing a specific external public server. The local host is 192.168.1.10 and the external public server is 100.100.100.1. We need to limit the traffic to 100kbps and burst size 8000.

Configuration Snippet:

ASA(config)#access-list rate-limit-acl extended permit ip host 192.168.1.10 host 100.100.100.1

ASA(config)#class-map rate-limit
ASA(config-cmap)#match access-list rate-limit-acl

ASA(config)#policy-map limit-policy
ASA(config-pmap)#class rate-limit
ASA(config-pmap-c)#police output 100000 8000

ASA(config)#service-policy limit-policy interface outside

In order to be able to monitor and troubleshoot your Cisco ASA firewall, you need to understand the difference between connections and translations.

Refer to the diagram above for an explanation about Connections and Translations.

A Connection works at the Transport Layer and includes the Source IP/Source Port and the Destination IP/Destination Port. Connections are subsets of Translations. You can have many connections open that are all using the same Translation. For example, a connection shown above is originated from Internal source host 192.168.1.1 with source port 1030 towards a Destination host (public Web Server) 100.100.100.1 on Destination Port 80.

A Translation works at the IP Layer and includes the Real IP Address and the Mapped (Translated) IP Address. Using NAT or PAT, a Real IP address is translated to a Mapped IP address and vice-versa. From the diagram above, the Real IP address 192.168.1.1 is translated to a Mapped IP address 20.20.20.1.

Connection Related Commands

ASA# show conn
ASA# show conn details
ASA# show local-host

The above commands will display the current active connections and information details about each connection. An example output is the following:

TCP outside:100.100.100.1/80 inside:192.168.1.1/1030 idle 0:00:05 bytes 1965 flags UIO

Translation Related Commands

ASA# show xlate
ASA# show xlate detail
ASA# clear xlate

The commands above enable you to display or clear the contents of the translation table. An example output is the following:

NAT from inside:192.168.1.1 to outside:20.20.20.1 flags i

A single Cisco ASA appliance can be partitioned into multiple virtual firewalls known also as “Security Contexts”. Each security context acts as a separate firewall with its own security policy, interfaces and configuration. However, some features are not available for virtual firewalls, such as IPSEC and SSL VPN, Dynamic Routing Protocols, Multicast and Threat Detection.

All firewall models (except ASA 5505) support multiple security contexts. By default, all models support 2 security contexts without a license upgrade (except the ASA 5510 which requires the security plus license).

When you convert the appliance from single context mode to multiple context mode (using the command “mode multiple“) the firewall converts the current running configuration into two files: a new startup configuration that comprises the system configuration, and “admin.cfg” that comprises the admin context (stored in the root directory of the internal Flash memory). The original running configuration is saved as “old_running.cfg” (in the root directory of the internal Flash memory).

Configuring Security Contexts

! Enable multiple context mode
ASA(config)# mode multiple

! Then reboot the appliance.

! Configure the administrator context
ASA(config)# admin-context administrator
ASA(config)# context administrator
ASA(config-ctx)# allocate-interface gigabitethernet0/1.10
ASA(config-ctx)# allocate-interface gigabitethernet0/1.11
ASA(config-ctx)# config-url flash:/admin.cfg

! Configure other contexts as required
ASA(config)# context customerA
ASA(config-ctx)# allocate-interface gigabitethernet0/2.100
ASA(config-ctx)# allocate-interface gigabitethernet0/2.200
ASA(config-ctx)# config-url flash:/customerA.cfg

! Configure other contexts as required
ASA(config)# context customerB
ASA(config-ctx)# allocate-interface gigabitethernet0/2.111
ASA(config-ctx)# allocate-interface gigabitethernet0/2.222
ASA(config-ctx)# config-url flash:/customerB.cfg

Changing between contexts and the system execution space:

When you connect with a console cable on the appliance, you will log in the system configuration (or the system execution space). The “system execution space” is the global appliance space from where you can then enter into specific security contexts. If you are logged in the “system execution space” and issue a “show run” command, this will ONLY show you the global system configuration and NOT the various security contexts configurations. You will need to log into a specific security context in order to change or see its configuration.

To change between the system execution space and a context, or between contexts, see the following commands:

! To change to a context named CustomerA, enter the following command:
ASA# changeto context CustomerA

! The prompt changes to the following:
ASA/CustomerA#

! To change back to the system execution space, enter the following command:
ASA/CustomerA# changeto system

! The prompt changes to the following:
ASA#

If you have lost the administrator password to access the security appliance you can recover the password with the following steps:

Step1: Connect to the firewall using a console cable

Step2: Power cycle the appliance (power off and then on)

Step3: Press the Escape key to enter ROMMON mode

Step4: Use confreg command to change the configuration register to 0×41

rommon #1> confreg 0×41

Step5:  Configure the security appliance to ignore the startup configuration.

rommon #2> confreg

The ASA firewall will display the current configuration register value and boot parameters and ask you if you want to change them

Current Configuration Register: 0×00000041

Configuration Summary:

  boot default image from Flash

  ignore system configuration 

Do you wish to change this configuration? y/n [n]: y

Step6: At the prompt enter Y to change the parameters.

Step7: Accept the default values for all settings (at the prompt enter Y)

Step8: Reload the ASA appliance by entering the following command

rommon #3> boot

The firewall will reboot and load the default configuration instead of the startup configuration.

Step9:   Enter into EXEC mode

hostname> enable

When prompted for the password, press Enter (the password in blank now)

Step 10: Access the global configuration mode and change the passwords as required:

hostname# configure terminal
hostname(config)# password password
hostname(config)# enable password password
hostname(config)# username name password password

Step 11: Load the default configuration register value (0×1) by entering the following command:

hostname(config)# no config-register

Step 12: Save the new passwords to the startup configuration by entering the following command:

hostname(config)# copy running-config startup-config

If for any reason the software image on your Cisco ASA appliance is corrupted and the device does not boot to normal operating mode, then you can load a new image using ROMMON (ROM monitor mode) and TFTP. Follow the steps below to get into ROMMON mode and then assign all necessary settings for uploading the new image file:

Step1: Connect to the ASA firewall using a console cable.

Step2: Power off the appliance and then power it on.

Step3: When the appliance starts, press the Escape key on your keyboard to force the appliance to enter ROMMON mode.

Step4: In ROMMON mode, configure all necessary settings for connecting to the TFTP server to load the new image. You need to connect a PC with TFTP server on a firewall port (e.g Ethernet0/0). Then enter the following commands on the ASA.

rommon #1> ADDRESS=192.168.1.10
rommon #2> SERVER=192.168.1.1
rommon #3> GATEWAY=192.168.1.1
rommon #4> IMAGE=asa800-232-k8.bin
rommon #5> PORT=Ethernet0/0
 

The above configuration will assign an IP address of 192.168.1.10 to interface Ethernet0/0 of the firewall appliance. It will also tell the firewall that the TFTP SERVER is at address 192.168.1.1 and the image to load is asa800-232-k8.bin

Step5: Execute the TFTP upload from the ASA using:

rommon #6> tftp

The above instructs the firewall to start uploading the image file from TFTP.

After the firewall reboots, login and check that the new image has been installed (show version)