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Difficulty: MediumInside Source NAT and PAT Configuration and Verification

A network administrator is configuring Port Address Translation (PAT) on an enterprise Cisco IOS router. The internal subnets matched by Access Control List 15 require multiple internal IP addresses to share a dynamic pool of public IPv4 addresses named GUESTNATPOOLGUEST_NAT_POOL. Which Cisco IOS global configuration command correctly enables PAT using this dynamic address pool?

  1. ip nat inside source list 15 pool GUEST_NAT_POOL overloadAnswer
  2. B
    ip nat inside source list 15 pool GUEST_NAT_POOL
  3. C
    ip nat outside source list 15 pool GUEST_NAT_POOL overload
  4. D
    ip nat inside source static list 15 pool GUEST_NAT_POOL overload

Answer

The correct command to configure dynamic PAT using an IP address pool is 'ip nat inside source list 15 pool GUEST_NAT_POOL overload'.
The correct command syntax for dynamic NAT with PAT using an IP address pool is 'ip nat inside source list <acl-number> pool <pool-name> overload'. The 'overload' keyword enables Layer 4 source port tracking so multiple internal IP addresses can share the IP addresses in the pool simultaneously.

Step-by-Step Solution

1
Identify the source direction and dynamic NAT type
Inside source traffic matching an ACL requires 'ip nat inside source list <ACL>'.
Internal private hosts initiating outbound connections must undergo inside source NAT.
2
Specify the target public address pool
Append 'pool GUEST_NAT_POOL' to map matching ACL traffic to the designated pool.
The scenario requires using a pre-defined named pool of public IP addresses instead of a single interface.
3
Enable port multiplexing (PAT)
Append the 'overload' keyword at the end of the command.
Without 'overload', Cisco IOS configures standard dynamic NAT (1-to-1 translation), whereas PAT (many-to-one/many-to-few using layer 4 ports) explicitly requires 'overload'.

Key Concept

Port Address Translation (PAT) pool configuration using the overload keyword
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Topics

Inside Source NAT and PAT Configuration and Verification

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