Cisco Certified Support Technician (CCST) NetworkingIP ConnectivityMedium
A network technician is configuring a Cisco router to perform Port Address Translation (PAT) for internal users accessing the internet. Which of the following commands correctly defines the inside global interface for PAT?
- Aip nat outside source list 1 interface GigabitEthernet0/1 overload
- Bip nat inside source list 1 interface GigabitEthernet0/1 overload
- Cip nat enable
- Dip nat pool NAT_POOL 203.0.113.1 203.0.113.1 netmask 255.255.255.252
Show answer & explanationAnswer & explanation
Correct answer: B. ip nat inside source list 1 interface GigabitEthernet0/1 overload
The 'inside global' interface is the interface connected to the public network, where the translated addresses appear. The command 'ip nat inside source list <access-list-number> interface <interface-id> overload' correctly configures PAT using the IP address of the specified interface for translation.
Why the other options are wrong
- A. This command incorrectly uses 'outside' instead of 'inside' for the source translation, which is used for dynamic NAT with a pool, not PAT using an interface.
- C. This is not a valid Cisco IOS command for configuring NAT; NAT is enabled on interfaces using 'ip nat inside' and 'ip nat outside'.
- D. This command defines a NAT pool, which is used for dynamic NAT or static NAT, not for PAT using a single interface's IP address.
Cisco IOS PAT Configuration
Port Address Translation (PAT) on Cisco IOS allows multiple private IP addresses to share a single public IP address by using different port numbers.
- Uses 'ip nat inside source list <acl> interface <interface> overload' for one-to-many translation.
- Requires 'ip nat inside' and 'ip nat outside' commands on respective interfaces.
- Saves public IP addresses by mapping multiple private IPs to a single public IP and unique port numbers.
Memory trick: PAT: 'I'm In, Source, List, Interface, Overload' to get Out!