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Difficulty: MediumNAT and PAT Implementation

An administrator is inspecting the Network Address Translation (NAT) table on an enterprise border router to resolve a host connectivity issue. The CLI display shows the following active translation entry:

Inside global: 198.51.100.14:51022∣Inside local: 10.0.4.15:51022\text{Inside global: } 198.51.100.14:51022 \quad | \quad \text{Inside local: } 10.0.4.15:51022
Outside local: 198.51.100.80:80∣Outside global: 198.51.100.80:80\text{Outside local: } 198.51.100.80:80 \quad | \quad \text{Outside global: } 198.51.100.80:80

Which IPv4 address represents the private address assigned directly to the internal host on the local network before translation occurs?

  1. 10.0.4.15Answer
  2. B
    198.51.100.14
  3. C
    198.51.100.80
  4. D
    51022

Answer

10.0.4.15 represents the Inside Local address, which is the un-translated private IPv4 address configured directly on the internal host.
In standard network address translation terminology, 'Inside Local' refers specifically to the private IP address assigned to a host on the internal network. In the provided translation table, 10.0.4.15 is listed under Inside Local, making it the un-translated private IPv4 address of the local client.

Step-by-Step Solution

1
Identify the standard CompTIA / Cisco NAT terminology components in the translation table
Inside Local is defined as the IP address assigned to a host on the inside network; Inside Global is the translated public IP address of the inside host.
Understanding NAT address categories is required to interpret translation tables.
2
Locate the 'Inside local' field in the translation output
The entry displays 'Inside local: 10.0.4.15:51022'.
The IP portion preceding the colon indicates the Layer 3 host IP address on the internal network segment.
3
Extract the IP address from the Inside Local socket pair
10.0.4.15 is isolated as the client private address.
Port 51022 is the ephemeral Layer 4 port used by PAT, while 10.0.4.15 is the private IPv4 host address.

Key Concept

NAT / PAT Address Types (Inside Local, Inside Global, Outside Local, Outside Global)
Estimated Time:1m 15s
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Topics

NAT and PAT Implementation

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