Cisco CCNA (200-301)IP ServicesMedium
Refer to the following router output: ``` Router# show ip nat translations Pro Inside global Inside local Outside local Outside global icmp 203.0.113.10:1 10.0.0.1:1 198.51.100.5:1 198.51.100.5:1 icmp 203.0.113.10:2 10.0.0.2:2 198.51.100.6:2 198.51.100.6:2 tcp 203.0.113.11:1024 10.0.0.3:1024 192.0.2.1:80 192.0.2.1:80 ``` Which statement about the NAT configuration is true?
- AHost 10.0.0.3 is initiating a web (HTTP) connection to 192.0.2.1.
- BHost 10.0.0.1 is communicating with an external server 198.51.100.5 using the global IP 203.0.113.1.
- CThe router is configured for PAT, allowing multiple internal hosts to share 203.0.113.10.
- DThe router is configured for static NAT for the first two entries.
Show answer & explanationAnswer & explanation
Correct answer: A. Host 10.0.0.3 is initiating a web (HTTP) connection to 192.0.2.1.
The third entry shows a TCP connection where `Inside local` 10.0.0.3, using port 1024, is translated to `Inside global` 203.0.113.11, also on port 1024. This connection is destined for `Outside local` (and `Outside global`) 192.0.2.1 on port 80 (HTTP). This indicates 10.0.0.3 is initiating a web request.
Why the other options are wrong
- B. Host 10.0.0.1 is using `Inside global` 203.0.113.10, not 203.0.113.1.
- C. While the output implies PAT (especially from the ICMP entries sharing 203.0.113.10), the statement claims multiple internal hosts are sharing 203.0.113.10. While 10.0.0.1 and 10.0.0.2 do share it, 10.0.0.3 uses 203.0.113.11. So, not all hosts share *that specific* IP, making the statement partially incorrect or at least not fully accurate for the entire table.
- D. The first two entries show ICMP traffic where two different internal IPs (10.0.0.1 and 10.0.0.2) are using the *same* `Inside global` IP (203.0.113.10) but different port numbers (1 and 2, which are ICMP ID numbers here). This indicates PAT (or dynamic NAT with PAT for ICMP), not static NAT where each private IP would have its own public IP.
NAT Translation Table Interpretation
Understanding the fields in `show ip nat translations` output to determine translation types, source/destination IPs, and ports.
- `Inside local`: Original source IP/port of internal host.
- `Inside global`: Translated source IP/port used externally.
- `Outside local`: Original destination IP/port of external host.
- `Outside global`: Translated destination IP/port (often same as outside local).
Memory trick: Inside to Global, Outside to Outside, Follow the Ports to know the Route.