Cisco ASA Basic Configuration Guide



Table of Contents


1.1.       Introduction to CISCO ASA 5520 Configuration Example
1.2.       Initial Configuration
1.3.       Null modem cable
1.4.       Serial link on laptop
1.5.       Connection to the device
1.6.       Terminal Emulation Software Settings for hyper teminal
1.7.       Hostname domain name and ssh keys generation
1.8.       Management interface
1.9.       Upgrade the Cisco IOS
1.10.     Management Gui Configuration
1.11.     Basic Static Routing Configuration
1.12.     Basic Global Natting Configuration
1.13.     More complex Cisco NATing Concepts
1.14.     Basic Access list Configuration
1.15.     Basic Troubleshooting commands enabling
1.16.     Viewing the logs on the Cisco ASA appliance
1.17.     Best Practice management Configuration suggestions
1.18.     More advanced best practices and hardening confiuguration guide


Introduction to CISCO ASA 5520 Configuration Example



The bellow is a quick start to get your Cisco ASA off the ground by the means of a few print screens
It provides  an easier way of explaining how to connect to the system for common tasks without the pain of having to know to know complex intimidating techniques.

The bellow section will guide you step by step trough configuring and administering a simple Cisco ASA installation including common configurations like :

Initial Configuration



Null modem cable


Firstly you will need a cisco console cable as shown bellow cable null modem cal be as show below



Serial link on laptop


You will need a computer or a laptop with a serial connection to connect to the cisco asa 5520 appliance in order to manage it




Connection to the device


Before you can perform the initial configuration of the Cisco ASA you must establish a serial console connection to it. terminal emulation communication software (Hyper Terminal or equivalent).


Terminal Emulation Software Settings for hyper teminal


To establish a serial console connection, set your terminal emulation communication software to operate with the following settings






After Establishing a Serial connection a network cable needs to be plugged into the Cisco ASA as well as a serial console connection altogether it should look like that






The initial configuration of the device has to be done on the Command Line Interface and example of that is included bellow


Hostname domain name and ssh keys generation


First of all you need to configure the initial settings of the device with a hostname and a domain name in order to be able generate SSH usage keys

hostname test-asa
enable password ZdcH9lbXsA2JtS18 encrypted
passwd 2KFQnbNIdI.2KYOU encrypted
crypto key generate rsa usage-keys


Management interface


Then you need to configure the the management interface with an ip address in order to be able to connect to the computer you are managing the device from

interface Management0/0
speed 100
duplex full
nameif inside
security-level 100
ip address



Upgrade the Cisco IOS


Then you need to copy the latest release of the cisco IOS software for the appropriate appliance version from the TFTP server (usually your laptop's ip address here depicted as running a TFTP server that can be downloaded here)

copy tftp:// flash:

boot system disk0:/asa821-k8.bin


Management Gui Configuration


Then you you need to configure the ASDM gui management interface of the ASA .Bear in mind once the image file is copied to the flash of the device you also need to enable the http server and enable who is able to access the service


copy tftp:// flash:

asdm image disk0:/asdm-621.bin

http server enable

http 0 0 inside



Basic Static Routing Configuration


Then you need to configure the basic outside interface parameters as well as routing on the outside interface so you can communicate with the outside world.Once that's done you have to enable the transition of traffic from the inside interface trough a feature called network address translation or NAT.A lot of things have been written about nat i am not going to go trough all of them here suffice to say if you issue the bellow commands the translation will happen and you will be able to establish a bridge between the inside and the outside interfaces.

interface GigabitEthernet0/0
speed 100
duplex full
nameif outside
security-level 0
ip address



! the bellow command is used to enable default routing on the ASA device using as the default destination to send its traffic to

route outisde 0 0



Basic Global Natting Configuration


The natting feature is basically used on the Cisco ASA as measure of protecting your private network addresses when they are accessing the internet.Its achieved by the bellow commands

nat (inside) 1

global (outside) 1 interface


More complex Cisco NATing Concepts


The bellow Section Describes natting order of operation in more detail.Cisco ASA natting is considered one of the most complicated and challenging subjects .If it looks intimidating thats because it is .If you require some assistance with that you can always contact us for more info.

Order of NAT Commands Used to Match Real Addresses
The security appliance matches real addresses to NAT commands in the following order:


1. NAT exemption (nat 0 access-list)—In order, until the first match. Identity NAT is not included in this category; it is included in the regular static NAT or regular NAT category. We do not recommend overlapping addresses in NAT exemption statements because unexpected results can occur.


2. Static NAT and Static PAT (regular and policy) (static)—In order, until the first match. Static identity NAT is included in this category.


3. Policy dynamic NAT (nat access-list)—In order, until the first match. Overlapping addresses are


4. Regular dynamic NAT (nat)—Best match. Regular identity NAT is included in this category. The order of the NAT commands does not matter; the NAT statement that best matches the real address is used. For example, you can create a general statement to translate all addresses ( on an interface. If you want to translate a subset of your network ( to a different address, then you can create a statement to translate only When makes a connection, the specific statement for is used because it matches the real address best. We do not recommend using overlapping statements; they use more memory and can slow the performance of the security appliance.


Basic Access list Configuration


Then you you need to configure some access lists allowing certain hosts to access resources on the internet or other connected interfaces on the firewall.Then assign and apply that access group to the inside interface

access-list inside extended permit ip any any

access-group inside in interface inside


Basic Troubleshooting commands enabling


After that's done you have configured the basic settings on your ASA device .The bellow settings are recommended in order to troubleshoot simple connectivity and other issues you may encounter on the asa device by the ways of logging .The logging functionality on the ASA is extensive and is unparalleled in troubleshooting usefulness in determining where the problem lies .

logging enable
logging timestamp
logging buffer-size 999999
logging buffered debugging
logging trap debugging
logging history debugging
logging asdm debugging
logging facility 23


Viewing the logs on the Cisco ASA appliance


show logging | include


Best Practice management Configuration suggestions


A best practice would be to configure remote management access to a device by allowing only a few hosts to connect to the Cisco ASA device for remote management as shown bellow

ssh outside

ssh verion 2



Recommended Reading


  1. Cisco ACS Best Practices document
  2. Cisco ASA Best Practices and Security Hardening Document.
  3. Cisco-vpn-ipsec-configuration-examples
  4. Cisco-ids-ips-aip-idsm-configuration-examples
  5. Detailed Cisco ACS 5.2 installation and configuration example with print screens

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