The Six Simple Steps to a working ASA

Working with a Cisco ASA series can be daunting up front, especially when trying to configure it from the command line... but when you distill out all the fancy frills and extra features, there are really only six core components that need to be configured for a working firewall. Here they are:

Step1: Configure the internal interface vlan
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ASA5505(config)# interface Vlan 1
ASA5505(config-if)# nameif inside
ASA5505(config-if)# security-level 100
ASA5505(config-if)# ip address 192.168.1.1 255.255.255.0
ASA5505(config-if)# no shut

Step 2: Configure the external interface vlan (connected to Internet)
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ASA5505(config)# interface Vlan 2
ASA5505(config-if)# nameif outside
ASA5505(config-if)# security-level 0
ASA5505(config-if)# ip address 200.200.200.1 255.255.255.0
ASA5505(config-if)# no shut

Step 3: Assign Ethernet 0/0 to Vlan 2
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ASA5505(config)# interface Ethernet0/0
ASA5505(config-if)# switchport access vlan 2
ASA5505(config-if)# no shut

Step 4: Enable the rest interfaces with no shut
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ASA5505(config)# interface Ethernet0/1
ASA5505(config-if)# no shut
Do the same for Ethernet0/1 to 0/7.

Step 5: Configure PAT on the outside interface
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ASA5505(config)# global (outside) 1 interface
ASA5505(config)# nat (inside) 1 0.0.0.0 0.0.0.0

Step 6: Configure default route towards the ISP (assume default gateway is 200.200.200.2)
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ASA5505(config)# route outside 0.0.0.0 0.0.0.0 200.200.200.2 1