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Difficulty: MediumNAT and PAT Implementation

A systems engineer is configuring an edge router for a secondary data center. The site has 50 internal servers on the private IP range 10.20.0.0/2610.20.0.0/26 that require outbound Internet access to update external software repositories using a single public IP address (203.0.113.10203.0.113.10). Additionally, external administrators must be able to initiate inbound SSH connections directly to a dedicated internal management server at 10.20.0.510.20.0.5. Which combination of address translation implementations should the engineer configure on the edge router?

  1. Configure Port Address Translation (PAT / Overload) using public IP address 203.0.113.10203.0.113.10 for the 10.20.0.0/2610.20.0.0/26 subnet, and configure a static port translation rule mapping inbound TCP port 22 on 203.0.113.10203.0.113.10 to 10.20.0.510.20.0.5.Answer
  2. B
    Configure one-to-one Static NAT for all 50 hosts in the 10.20.0.0/2610.20.0.0/26 subnet using 203.0.113.10203.0.113.10, and rely on Dynamic NAT to handle incoming SSH requests.
  3. C
    Configure Dynamic NAT for outbound connections to automatically convert TCP port 22 into UDP port 22 across outgoing packet headers to bypass inbound firewall filters.
  4. D
    Configure Layer 2 Media Access Control address translation on the LAN switch interface to map internal MAC addresses directly to public IP addresses before routing frames.

Answer

Port Address Translation (PAT / Overload) should be configured for outbound host access sharing the public IP, along with a static port translation (port forwarding) mapping rule for inbound SSH access to the management server.
Port Address Translation (PAT / Overload) uses unique source port numbers at Layer 4 to allow multiple internal private IP addresses to share a single public IP address for outbound traffic. For inbound connections to internal resources, a static translation entry (such as port forwarding TCP port 22) must be created so the router knows which internal host should receive traffic initiated from external networks.

Step-by-Step Solution

1
Analyze outbound requirement for internal subnet
50 internal hosts on 10.20.0.0/2610.20.0.0/26 must share a single public IP (203.0.113.10203.0.113.10).
Because only one public IP address is available for 50 hosts, Layer 4 Port Address Translation (PAT / NAT Overload) is required to track separate connections by source port.
2
Analyze inbound requirement for internal management server
External clients must initiate SSH connections to 10.20.0.510.20.0.5 through 203.0.113.10203.0.113.10.
Inbound connections initiated from the outside require a static, predictable mapping. Static NAT or Static PAT (Port Forwarding on TCP port 22) routes incoming traffic on the public IP directly to the internal server's private address.
3
Combine translation methods on edge router
PAT handles outbound dynamic sessions; Static NAT/PAT handles inbound SSH sessions.
This dual implementation permits outbound internet browsing for all internal hosts while maintaining targeted inbound service accessibility.

Key Concept

Combining Port Address Translation (PAT/Overload) for outbound host multiplexing with Static NAT/Port Forwarding for inbound server availability.
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Topics

NAT and PAT Implementation

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