Secure Network Administrationadvanced
Which statement correctly distinguishes between Source NAT (SNAT) and Destination NAT (DNAT)?
Answer
SNAT modifies the source IP address of outbound packets to enable internal clients to access external networks, while DNAT modifies the destination IP address of inbound packets to expose internal servers to external clients.
Explanation
### What a good answer covers
- Source NAT changes the source address for outbound traffic from Internal or DMZ toward the Internet.
- In the lab, its translated source uses the firewall's Internet-facing interface address.
- Destination NAT changes the destination address for inbound web traffic.
- The HTTP and HTTPS mappings forward to the DMZ server at 172.16.10.10.
- Security policies separately permit the relevant traffic.
### The concept
The two NAT types are named for the packet field they change. An outbound client begins with its own source address, which Source NAT replaces for Internet access. An inbound web request begins with the firewall's public-facing destination address, which Destination NAT replaces with the server's address. This direction-based distinction helps identify which rule a scenario requires.
| NAT type | Address changed | Lab use |
|---|---|---|
| Source NAT | Source address | Outbound Internet access |
| Destination NAT | Destination address | Inbound forwarding to the DMZ web server |
### Terms
- **Port forwarding**: Sending traffic addressed to an external endpoint to a selected internal server.
- **DMZ**: Demilitarized Zone, a network segment for exposed services.
### Remember
Outbound clients usually need Source NAT; inbound server access uses Destination NAT.
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