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Difficulty: MediumInside Source NAT and PAT Configuration and Verification

An administrator configures dynamic NAT on a Cisco IOS router using a pool containing a single public IP address (203.0.113.100203.0.113.100) to enable Internet connectivity for internal workstations. During testing, only the first internal user who initiates outbound traffic can access external sites. All subsequent attempts from other internal users to access the Internet fail. Which action on the router resolves this connectivity issue?

  1. Append the `overload` keyword to the `ip nat inside source list <ACL> pool <POOL>` configuration command.Answer
  2. B
    Expand the internal access list to match the public IP range 172.32.0.0/12172.32.0.0/12 instead of RFC 1918 private space.
  3. C
    Reconfigure the translation using `ip nat inside source static` to dynamically allocate port numbers to the pool.
  4. D
    Swap the interface assignments so that the LAN interface is configured with `ip nat outside` and the WAN with `ip nat inside`.

Answer

Append the `overload` keyword to the global `ip nat inside source list <ACL> pool <POOL>` command to enable Port Address Translation (PAT).
When dynamic NAT is configured with an IP NAT pool containing a single public IP address, omitting the `overload` keyword restricts translations to a single 1-to-1 mapping. Once the first host initiates traffic, the single address in the pool is exhausted. Appending the `overload` keyword enables Port Address Translation (PAT), allowing multiple internal hosts to share the single IP address concurrently by tracking unique Layer 4 source port numbers.

Step-by-Step Solution

1
Analyze the symptom of dynamic NAT failure.
Without port translation enabled, dynamic NAT allocates pool IP addresses on a strict 1-to-1 basis. With a single public IP address in the pool, only one internal host receives a translation entry.
Determines why subsequent internal hosts fail to obtain an outbound translation.
2
Identify the required feature for many-to-one translation using a single IP address.
Port Address Translation (PAT) allows thousands of internal hosts to multiplex outbound connections over a single IP address using unique TCP/UDP source ports.
PAT is activated on Cisco IOS dynamic NAT configurations by appending the `overload` keyword.
3
Select the correct command modification.
Modifying the translation statement to include `overload` (`ip nat inside source list <ACL> pool <POOL> overload`) resolves the single-host limitation.
Applies PAT, enabling all internal hosts to share the single public IP address concurrently.

Key Concept

Port Address Translation (PAT) Overload Configuration
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Topics

Inside Source NAT and PAT Configuration and Verification

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