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Difficulty: MediumInside Source NAT and PAT Configuration and Verification

An administrator examines the following output from a Cisco router after configuring Network Address Translation to map private addresses to a defined address pool:

text
Router# show ip nat statistics
Total active translations: 1 (0 static, 1 dynamic; 0 extended)
Outside interfaces:
GigabitEthernet0/1
Inside interfaces:
GigabitEthernet0/0
Hits: 14 Misses: 0
Dynamic mappings:
-- Inside Source
[id 1] access-list 10 pool NAT_POOL refcount 1

Users on the internal subnet report that only one device at a time can successfully communicate with external networks. Which configuration change will resolve this issue and allow multiple concurrent internal hosts to share the translation pool?

  1. Append the overload keyword to the ip nat inside source list 10 pool NAT_POOL command.Answer
  2. B
    Add the overload keyword to the ip nat pool NAT_POOL command definition.
  3. C
    Modify Access Control List 10 to permit the public IP addresses contained within NAT_POOL.
  4. D
    Reassign interface GigabitEthernet0/0 as ip nat outside and GigabitEthernet0/1 as ip nat inside.

Answer

Append the overload keyword to the ip nat inside source list command to enable Port Address Translation.
The show ip nat statistics output reveals '0 extended translations', meaning the router is performing 1-to-1 dynamic NAT rather than Port Address Translation (PAT). Adding the overload keyword to the 'ip nat inside source list 10 pool NAT_POOL' statement enables port multiplexing, which permits multiple inside hosts to share pool addresses simultaneously.

Step-by-Step Solution

1
Analyze the output of show ip nat statistics.
The statistics show 0 extended translations and 1 dynamic translation, indicating standard dynamic NAT (1-to-1 mapping) rather than PAT.
Without extended translations, each internal host consumes an entire IP address from the pool, preventing other hosts from translating once pool addresses are checked out.
2
Identify the missing keyword in the NAT configuration.
The current dynamic mapping uses 'access-list 10 pool NAT_POOL' without 'overload'.
The 'overload' keyword instructs Cisco IOS to track transport layer port numbers, enabling multiple hosts to share single public IP addresses.
3
Select the correct command modification.
Reconfigure using 'ip nat inside source list 10 pool NAT_POOL overload'.
This enables PAT on the pool and allows concurrent outbound access for all hosts matching ACL 10.

Key Concept

Port Address Translation (PAT) / Inside Source NAT Overload Configuration
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Topics

Inside Source NAT and PAT Configuration and Verification

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