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Difficulty: EasyInside Source NAT and PAT Configuration and Verification

A network engineer is configuring Port Address Translation (PAT) on a Cisco IOS router using a dynamic interface-based configuration. The engineer enters the following global configuration command to map inside addresses matched by Access List 10 to the GigabitEthernet0/1 interface:

`ip nat inside source list 10 interface GigabitEthernet0/1`

Which single Cisco IOS keyword must be added to the end of this command to allow multiple internal hosts to share the single public IP address using unique source port numbers?

Answer: overload

Answer

overload
The `overload` keyword instructs Cisco IOS to perform Port Address Translation (PAT). PAT enables multiple inside local IP addresses to share a single inside global IP address (such as a router's outside interface address) by distinguishing traffic flows with unique source port numbers.

Step-by-Step Solution

1
Identify the goal of the configuration command.
The objective is to enable Port Address Translation (PAT) using the router interface's single public IPv4 address.
Without PAT enabled, dynamic NAT only performs 1-to-1 IP translations, which exhausts the single interface IP address after only one internal host translates.
2
Determine the required Cisco IOS command parameter for PAT.
Adding `overload` to the end of the `ip nat inside source` statement enables port-level multiplexing.
The `overload` keyword tells Cisco IOS to track Layer 4 TCP and UDP port numbers alongside IP addresses, allowing thousands of simultaneous internal connections on a single public IP.

Key Concept

Port Address Translation (PAT) Overload Keyword
Estimated Time:45s
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Topics

Inside Source NAT and PAT Configuration and Verification

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