A network technician is configuring PAT (Port Address Translation) on a Cisco router to allow multiple internal hosts to share a single public IP address. The router's public IP address is 203.0.113.1, and the internal network is 192.168.1.0/24. Which `ip nat inside source` command correctly configures PAT using an access list and the router's public interface?
- Aip nat outside source list 1 interface GigabitEthernet0/0 overload
- Bip nat inside source list 1 interface GigabitEthernet0/0 overload
- Cip nat inside source static 192.168.1.10 203.0.113.1
- Dip nat inside source list 1 pool NAT_POOL overload
Show answer & explanationAnswer & explanation
Correct answer: B. ip nat inside source list 1 interface GigabitEthernet0/0 overload
To configure PAT (overload) using an access list and the router's interface IP address, the command `ip nat inside source list <access-list-number> interface <interface-type-number> overload` is used. This tells the router to translate source IP addresses that match access-list 1, using the IP address of the specified outgoing interface, and to overload (PAT) for multiple internal hosts.
Why the other options are wrong
- A. `ip nat outside source` is incorrect; NAT translation occurs for 'inside' traffic going 'outside'.
- C. This command is for static NAT, which maps a single private IP to a single public IP, not PAT for multiple hosts.
- D. This command uses a NAT pool, which is for dynamic NAT with a pool of public IPs, not necessarily for overloading a single interface IP, and the question implies using the router's public interface address directly.
Cisco IOS PAT Configuration
Configuring Port Address Translation (PAT) in Cisco IOS typically involves defining inside/outside interfaces, an access list for internal hosts, and the `ip nat inside source` command with the `overload` keyword.
- Uses `ip nat inside source` command.
- `overload` keyword enables PAT.
- Can use an access list to define translatable internal IPs.
- Can use an interface's IP or a NAT pool for translation.
Memory trick: PAT is like a doorman (router) for many guests (internal IPs) sharing one exit (public IP).