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Difficulty: EasyInside Source NAT and PAT Configuration and Verification

A network administrator is configuring Port Address Translation (PAT) on a Cisco IOS router. Internal private IP hosts defined in Access Control List 1 (ACL 1) must share the single public IPv4 address assigned to the GigabitEthernet0/0 interface when communicating with the internet. Which Cisco IOS global configuration command correctly enables PAT for this scenario?

  1. ip nat inside source list 1 interface GigabitEthernet0/0 overloadAnswer
  2. B
    ip nat inside source list 1 interface GigabitEthernet0/0
  3. C
    ip nat inside source list 1 pool PUBLIC_POOL netmask 255.255.255.0
  4. D
    ip nat outside source list 1 interface GigabitEthernet0/0 overload

Answer

The command 'ip nat inside source list 1 interface GigabitEthernet0/0 overload' correctly configures PAT using an egress interface's IPv4 address.
The command 'ip nat inside source list 1 interface GigabitEthernet0/0 overload' specifies that traffic matching ACL 1 coming from the inside interface should have its source address translated to the IP address configured on GigabitEthernet0/0. The inclusion of the 'overload' keyword enables Port Address Translation (PAT), allowing multiple internal devices to simultaneously share the single public IP address via layer 4 port tracking.

Step-by-Step Solution

1
Identify the translation direction and source identifier.
Internal traffic is identified by ACL 1, requiring 'ip nat inside source list 1'.
Inside source NAT identifies traffic originating from the internal network for translation.
2
Specify the target public IP source.
The target is the address on interface GigabitEthernet0/0, using 'interface GigabitEthernet0/0'.
When a dedicated public IP pool is not available or the ISP dynamically assigns an interface IP, NAT maps traffic directly to that interface.
3
Enable port-level multiplexing (PAT).
Append the 'overload' keyword at the end of the statement.
The 'overload' keyword allows thousands of internal IP addresses to share a single public IP address by tracking unique TCP/UDP source port numbers.

Key Concept

Configuring Inside Source Port Address Translation (PAT) with an interface address
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Topics

Inside Source NAT and PAT Configuration and Verification

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