How to setup the internet access through the Cisco ASA firewall?

Basic Guidelines for setting Internet through the Cisco ASA firewall:

At first we need to configure the interfaces on the firewall.

!— Configure the outside interface.

interface GigabitEthernet0/0
nameif outside
security-level 0
ip address

!— Configure the inside interface.

interface GigabitEthernet0/1
nameif inside
security-level 100
ip address

The nameif command gives the interface a name and assigns a security level. Typical names are outside, inside, or DMZ.

Security levels are numeric values, ranging from 0 to 100, used by the appliance to control traffic flow. Traffic is permitted to flow from interfaces with higher security levels to interfaces with lower security levels, but not the other way. Access-lists must be used to permit traffic to flow from lower security levels to higher security levels. The default security level for an outside interface is 0. For an inside interface, the default security level is 100.

IP address- IP address of interface

The next step will be to setup the nat & route

!— Creates an object called OBJ_GENERIC_ALL.
!— Any host IP not already matching another configured
!— NAT rule will Port Address Translate (PAT) to the outside interface IP
!— on the ASA (or for Internet bound traffic.
object network OBJ_GENERIC_ALL
nat (inside,outside) source dynamic OBJ_GENERIC_ALL interface
route outside

The nat statement, as shown above, tells the firewall to allow all traffic flowing from the inside to the outside interface to use whatever address is dynamically (DHCP) configured on the outside interface.

In the route statement at the end if you use the word interface instead the traffic is pat to firewall interface ‘route outside interface’

The last step is to add the access-list to permit traffic.

Create the simple access-list to allow inside network access to internet.

hostname (config)# object-group service allow_internet_tcp tcp
hostname (config-service)# description allow tcp ports for allowing access internet access
hostname (config-service)# port-object eq 80
hostname (config-service)# port-object eq 443
hostname (config)# object-group service allow_internet_udp udp
hostname (config-service)# description allow udp ports for allowing access internet access
hostname (config-service)# port-object eq DNS

access-list INSIDE-IN extended permit tcp <inside network >any eq allow_internet_tcp
access-list INSIDE-IN extended permit tcp <inside network>any eq allow_internet_udp