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Difficulty: MediumInside Source NAT and PAT Configuration and Verification

A network administrator is configuring Port Address Translation (PAT) on a Cisco IOS router. Internal hosts on subnet 10.45.10.0/2410.45.10.0/24 connect to interface `GigabitEthernet0/0/0`, while interface `GigabitEthernet0/0/1` connects to the Internet Service Provider. Standard access list 10 has been configured with `access-list 10 permit 10.45.10.0 0.0.0.255`. Which TWO configurations are required on the router to correctly enable inside source PAT sharing the public IPv4 address of `GigabitEthernet0/0/1`?

  1. Execute `ip nat inside source list 10 interface GigabitEthernet0/0/1 overload` in global configuration mode.Answer
  2. Configure `ip nat outside` under interface configuration mode for `GigabitEthernet0/0/1`.Answer
  3. C
    Execute `ip nat inside source list 10 interface GigabitEthernet0/0/1` in global configuration mode.
  4. D
    Configure `access-list 10 permit 172.32.10.0 0.0.0.255` to permit internal private RFC 1918 addresses.

Answer

The two required configurations are executing 'ip nat inside source list 10 interface GigabitEthernet0/0/1 overload' in global configuration mode and configuring 'ip nat outside' on interface GigabitEthernet0/0/1.
Configuring 'ip nat inside source list 10 interface GigabitEthernet0/0/1 overload' in global configuration mode combined with applying 'ip nat outside' to interface GigabitEthernet0/0/1 completes the mandatory steps to translate internal source traffic matching ACL 10 across the ISP interface using Port Address Translation.

Step-by-Step Solution

1
Identify the required global configuration statement for interface-based PAT.
The command 'ip nat inside source list 10 interface GigabitEthernet0/0/1 overload' correctly binds ACL 10 to the WAN interface and specifies port overload.
The 'overload' keyword allows thousands of internal sockets to share the single IP address assigned to GigabitEthernet0/0/1 using distinct layer 4 port numbers.
2
Identify interface NAT boundary designations.
Interface GigabitEthernet0/0/0 requires 'ip nat inside', and external interface GigabitEthernet0/0/1 requires 'ip nat outside'.
Cisco IOS NAT routing decisions require explicit identification of which interfaces face the inside private network and which interface faces the outside public network.

Key Concept

Inside Source Port Address Translation (PAT) using an Interface
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Topics

Inside Source NAT and PAT Configuration and Verification

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