Cisco CCNA NAT for IPv4 3 — Questions and Answers
Question 1: Which NAT address term describes the IP address of an external host as seen from the inside network?
- Inside local
- Inside global
- Outside local (Correct answer)
- Outside global
Correct answer: Outside local
The outside local address is how an external host's IP appears to the inside network, which may differ from its true public IP if destination NAT is used.
Question 2: A PAT table has exhausted all available port numbers for a given public IP. What happens to new connection attempts?
- The router queues them until ports free up
- New translations fail and connections are dropped (Correct answer)
- The router automatically allocates a second public IP
- ICMP redirect messages are sent to hosts
Correct answer: New translations fail and connections are dropped
When all ~65,535 ports are in use for a PAT address, no new translations can be created and new connections from inside hosts are dropped.
Question 3: Which statement correctly distinguishes Dynamic NAT from PAT?
- Dynamic NAT uses port numbers; PAT uses one-to-one mappings
- Dynamic NAT maps one private IP to one available pool address; PAT maps many private IPs to one address using ports (Correct answer)
- Dynamic NAT is only for outbound traffic; PAT works bidirectionally
- Dynamic NAT requires static configuration per host; PAT does not
Correct answer: Dynamic NAT maps one private IP to one available pool address; PAT maps many private IPs to one address using ports
Dynamic NAT creates a one-to-one mapping from a pool of public IPs; PAT maps multiple private IPs to a single public IP distinguished by unique port numbers.
Question 4: Which protocol does NAT handle differently because it has no port number in its header?
- TCP
- UDP
- ICMP (Correct answer)
- GRE
Correct answer: ICMP
ICMP lacks TCP/UDP port numbers, so PAT uses the ICMP query identifier field to differentiate multiple inside hosts sharing one public IP.
Question 5: What is the maximum number of simultaneous PAT translations theoretically possible per public IP address?
- 1,024
- 16,384
- 65,535 (Correct answer)
- 131,072
Correct answer: 65,535
PAT can theoretically support up to 65,535 simultaneous translations per public IP address, one per unique port number in the valid port range.
Question 6: A host on 192.168.1.10 sends a packet. After NAT, the outside sees source IP 203.0.113.5:4500. What NAT type is in use?
- Static NAT
- Dynamic NAT
- PAT (Correct answer)
- Twice NAT
Correct answer: PAT
The presence of a port number (4500) appended to the translated public IP is the signature of PAT (Port Address Translation / NAT Overload).
Question 7: Which command would you use to see how many NAT translations have been performed and how many have missed (no match)?
- show ip nat translations
- show ip nat statistics (Correct answer)
- debug ip nat detailed
- show ip interface brief
Correct answer: show ip nat statistics
'show ip nat statistics' shows hit/miss counts, the number of active translations, and which interfaces are inside/outside.
Cisco CCNA NAT for IPv4 3
Which NAT address term describes the IP address of an external host as seen from the inside network?