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300-410 Practice Question: According to RFC 2663, what is the term for the…
According to RFC 2663, what is the term for the process of translating both the source and destination IP addresses in a packet?
⚠ Common exam trap
Many candidates confuse 'Twice NAT' with 'Double NAT' — Cisco often tests this distinction, where Double NAT implies two separate NAT devices in series, while Twice NAT is a single device performing bidirectional translation as defined in RFC 2663.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Twice NAT
RFC 2663 defines 'Twice NAT' as the process of translating both the source and destination IP addresses within a single packet. This is necessary when the private and public address spaces overlap, requiring simultaneous translation of both the source and destination fields to ensure proper routing and reachability.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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Static NAT
Why it's wrong here
Static NAT maps one private address to one public address permanently, leaving the other address field untouched; it never translates both source and destination addresses. It is tempting because static NAT is the correct choice for publishing an internal server, such as a mail or web host, at a fixed externally reachable address.
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Twice NAT
Why this is correct
RFC 2663 defines Twice NAT as translating both source and destination addresses within the same packet, typically to resolve overlapping address space or redirect traffic. Basic NAT and NAPT translate only the source address or source port.
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PAT
Why it's wrong here
PAT, per RFC 2663, translates transport identifiers (ports) to multiplex many private hosts onto one public address; it does not translate both source and destination IP addresses. It is tempting because PAT is the everyday NAT variant on home routers, and it would be the right answer if the question asked how many hosts share a single public IP.
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Double NAT
Why it's wrong here
Double NAT describes two successive NAT translations along a path, not the simultaneous translation of source and destination addresses within one operation. It is tempting because the name suggests translating twice, but the RFC 2663 term for translating both addresses together is twice NAT.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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