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Difficulty: HardInside Source NAT and PAT Configuration and Verification

During network troubleshooting on router R3, users on subnet 172.16.10.0/24172.16.10.0/24 report that only one internal host can access the Internet at a time. The network administrator runs `show ip nat statistics` and observes the following output:

Total active translations: 1 (0 static, 1 dynamic, 0 extended)
Outside interfaces:
GigabitEthernet0/1
Inside interfaces:
GigabitEthernet0/0
Hits: 142 Misses: 18
Dynamic mappings:
-- Inside Source
access-list 15 pool CORP_PAT refcount 1

The running configuration contains:
`ip nat pool CORP_PAT 203.0.113.10 203.0.113.10 prefix-length 29`
`ip nat inside source list 15 pool CORP_PAT`

Which configuration change on R3 will resolve the issue and permit multiple internal hosts to access external resources simultaneously?

  1. Add overload to the end of the ip nat inside source list 15 pool CORP_PAT statement.Answer
  2. B
    Modify access-list 15 to reference public IP subnet 172.32.10.0/24 instead of private IP subnet 172.16.10.0/24.
  3. C
    Reconfigure GigabitEthernet0/0 with ip nat outside and GigabitEthernet0/1 with ip nat inside.
  4. D
    Append an explicit deny statement at the end of access-list 15 to clear stagnant NAT translation slots.

Answer

Add overload to the end of the ip nat inside source list 15 pool CORP_PAT statement.
The output of `show ip nat statistics` shows '0 extended translations', confirming that standard dynamic 1-to-1 NAT is running instead of Port Address Translation (PAT). Because the NAT pool contains only a single public IPv4 address (203.0.113.10203.0.113.10), omitting the `overload` parameter limits translation to only one internal host at a time. Appending `overload` to the `ip nat inside source list` command instructs the router to track Layer 4 port numbers, enabling multiple internal hosts to share the single public address simultaneously.

Step-by-Step Solution

1
Analyze the show ip nat statistics output.
Output shows 0 extended translations and 1 dynamic translation active.
An extended translation indicates PAT (layer 4 port tracking). Having 0 extended translations means standard 1-to-1 dynamic NAT is active.
2
Inspect the NAT pool and inside source command configuration.
The NAT pool CORP_PAT contains only one public IP address (203.0.113.10), and the translation rule lacks the overload keyword.
Without overload, standard dynamic NAT allocates the single pool address to the first host that generates traffic and exhausts the pool.
3
Determine the required CLI command modification.
Executing ip nat inside source list 15 pool CORP_PAT overload enables Port Address Translation.
Including overload allows multiple inside local IP addresses to share the single inside global IP address by tracking unique TCP/UDP port numbers.

Key Concept

Inside Source Port Address Translation (PAT) Configuration with NAT Pools
Estimated Time:2m 0s
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Topics

Inside Source NAT and PAT Configuration and Verification

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