Configuration Guide 5. NAT and NAPT
Version 7.2 19 Security Setup
5 NAT and NAPT
The device supports the NAT and PAT protocols. The PAT protocol for the device is
addressed as Network Address and Port Translation (NAPT). NAT changes the inside
address of your network with an external address. NAPT changes the inside addresses of
your network with a single external address with several ports.
NAT and NAPT provide two major benefits:
The inside of a network behind NAT or NAPT is hidden and cannot be accessed from
outside networks.
Saves IP addresses on the Internet, by using one address toward the outside and
many addresses on the inside.
By default, NAPT is activated on the Gigabitethernet0/0 interface. To disable NAPT per
interface, use the following commands:
Table 5-1: NAT and NAPT Commands
Command Description
Configuration of ACLs is in the data level.
(config-data)# interface
gigabitethernet 0/0
Configure interface gigabitethernet0/0.
(conf-if-GE 0/0)# no napt
Disable NAPT on the interface.
After disabling NAPT on the interface, the interface becomes a routing interface and packets
from the inside IP addresses are forwarded using the routing table through the interface
gigabitethernet0/0.
Figure 5-1: NAPT and NAT Topology
In Figure 5-1: NAPT and NAT Topology, when NAPT is disabled, in every packet sent to the
server from the user, the source is the user's IP address. When NAPT is enabled, the source
IP of every packet is the IP address configured on the WAN interface. The WAN interface in
the example is port Gi0/0.
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