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Difficulty: Very hardInside Source NAT and PAT Configuration and Verification

A network administrator is implementing Port Address Translation (PAT) using an IP address pool on a Cisco IOS router. Internal devices belong to the 172.16.0.0/12172.16.0.0/12 private network range. Standard IP access list 1515 has already been created to identify inside traffic with the command `access-list 15 permit 172.16.0.0 0.15.255.255`. The public IP addresses assigned by the ISP for translation are 203.0.113.10203.0.113.10 through 203.0.113.14203.0.113.14 with subnet mask 255.255.255.248255.255.255.248. Which TWO configuration commands must be executed on the router to correctly instantiate the pool and map the inside ACL traffic to allow multiple internal hosts to share these public IP addresses simultaneously?

  1. ip nat pool OUTSIDE_POOL 203.0.113.10 203.0.113.14 netmask 255.255.255.248Answer
  2. ip nat inside source list 15 pool OUTSIDE_POOL overloadAnswer
  3. C
    ip nat inside source list 15 pool OUTSIDE_POOL
  4. D
    ip nat pool OUTSIDE_POOL 172.16.0.10 172.16.0.14 netmask 255.255.255.248

Answer

The correct commands are 'ip nat pool OUTSIDE_POOL 203.0.113.10 203.0.113.14 netmask 255.255.255.248' and 'ip nat inside source list 15 pool OUTSIDE_POOL overload'.
Configuring multi-host Port Address Translation (PAT) across an IP pool requires two key elements: first, defining the pool of available public IP addresses with its range and netmask ('ip nat pool OUTSIDE_POOL 203.0.113.10 203.0.113.14 netmask 255.255.255.248'), and second, referencing that pool in the inside source translation directive with the 'overload' keyword ('ip nat inside source list 15 pool OUTSIDE_POOL overload').

Step-by-Step Solution

1
Define the public NAT IP address pool
Configured 'ip nat pool OUTSIDE_POOL 203.0.113.10 203.0.113.14 netmask 255.255.255.248'
Establishes the range of publicly routable IPv4 addresses provided by the ISP available for translation.
2
Map the access list traffic to the pool using Port Address Translation
Executed 'ip nat inside source list 15 pool OUTSIDE_POOL overload'
Binds the traffic identified in ACL 15 to the public pool and uses the 'overload' keyword to track unique layer 4 port numbers, enabling many private IP addresses to share the pool addresses.

Key Concept

Inside Source Dynamic PAT Configuration with Address Pool
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Topics

Inside Source NAT and PAT Configuration and Verification

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