Basic configuration tutorial for a Cisco ASA 5510 firewall. Learn how to configure Cisco ASA 5510 to get up and running.

1. How to Configure a Cisco ASA 5510 Firewall
– Basic Configuration Tutorial
This article gets back to the basics regarding Cisco ASA firewalls. I’m offering
you here a basic configuration tutorial for the Cisco ASA 5510 security appliance.
This device is the second model in the ASA series (ASA 5505, 5510, 5520 etc) and
is fairly popular since is intended for small to medium enterprises. Like the
smallest ASA 5505 model, the 5510 comes with two license options: The Base
license and the Security Plus license. The second one (security plus) provides some
performance and hardware enhancements over the base license, such as 130,000
Maximum firewall connections (instead of 50,000), 100 Maximum VLANs
(instead of 50), Failover Redundancy, etc. Also, the security plus license enables
two of the five firewall network ports to work as 10/100/1000 instead of only
10/100.
Next we will see a simple Internet Access scenario which will help us to
understand the basic steps needed to setup an ASA 5510. Assume that we are
assigned a static public IP address 100.100.100.1 from our ISP. Also, the internal
LAN network belongs to subnet 192.168.10.0/24. Interface Ethernet0/0 will be
connected to the outside (towards the ISP), and Ethernet0/1 will be connected to
the Inside LAN switch. Refer to the diagram below for our example scenario.

2. The firewall will be configured to supply IP addresses dynamically (using DHCP)
to the internal hosts. All outbound communication (from inside to outside) will be
translated using Port Address Translation (PAT) on the outside public interface.
Let’s see a snippet of the required configuration steps for this basic scenario:
Step1: Configure a privileged level password (enable password)
By default there is no password for accessing the ASA firewall, so the first step
before doing anything else is to configure a privileged level password, which will
be needed to allow subsequent access to the appliance. Configure this under
Configuration Mode:
ASA5510(config)# enable password mysecretpassword

3. Step2: Configure the public outside interface
ASA5510(config)# interface Ethernet0/0
ASA5510(config-if)# nameif outside
ASA5510(config-if)# security-level 0
ASA5510(config-if)# ip address 100.100.100.1 255.255.255.252
ASA5510(config-if)# no shut
Step3: Configure the trusted internal interface
ASA5510(config)# interface Ethernet0/1
ASA5510(config-if)# nameif inside
ASA5510(config-if)# security-level 100
ASA5510(config-if)# ip address 192.168.10.1 255.255.255.0
ASA5510(config-if)# no shut
Step 4: Configure PAT on the outside interface
ASA5510(config)# global (outside) 1 interface
ASA5510(config)# nat (inside) 1 0.0.0.0 0.0.0.0
UPDATE for ASA Version 8.3 and later (including ASA 9.x)
From March 2010, Cisco announced the new Cisco ASA software version 8.3.
This version introduced several important configuration changes, especially on the
NAT/PAT mechanism. The “global” command is no longer supported. NAT (static
and dynamic) and PAT are configured under network objects. The PAT
configuration below is for ASA 8.3 and later:
object network obj_any
subnet 0.0.0.0 0.0.0.0
nat (inside,outside) dynamic interface

4. Step 5: Configure Default Route towards the ISP (assume default gateway is
100.100.100.2)
ASA5510(config)# route outside 0.0.0.0 0.0.0.0 100.100.100.2 1
Step 6: Configure the firewall to assign internal IP and DNS address to hosts
using DHCP
ASA5510(config)# dhcpd dns 200.200.200.10
ASA5510(config)# dhcpd address 192.168.10.10-192.168.10.200 inside
ASA5510(config)# dhcpd enable inside
The above basic configuration is just the beginning for making the appliance
operational. There are many more configuration features that you need to
implement to increase the security of your network, such as Static and Dynamic
NAT, Access Control Lists to control traffic flow, DMZ zones, VPN etc. I just
tried to offer you a starting point for a basic configuration from where you can
build your knowledge further. For a more complete practical guide about Cisco
ASA Firewall configuration I suggest you to read the “Cisco ASA Firewall
Fundamentals – 3rd Edition” ebook.
About the Author
Harris Andrea is a Cisco Certified Professional with more than 18 years of
experience working with Cisco network technologies. He is the author of
two Cisco Books (“Cisco ASA Firewall Fundamentals” and “Cisco
VPN Configuration Guide”) which have been embraced by thousands of
Cisco professionals all over the world. You can find more Cisco
configuration guides and tutorials on his blog here:
http://www.networkstraining.com