300-420 Question #338: Real Exam Question with Answer & Explanation

Question

Refer to the exhibit. An engineer must connect the IPv6 island to the IPv4-only network to provide IPv6 hosts access to file servers and DNS services in the IPv4 network. Which NAT should the engineer choose?

Options

• Astateless NAT66
• Bstateful NAT66
• Cdynamic NAT-PT
• Dstatic NAT-PT

Explanation

To connect an IPv6 island to an IPv4-only network, providing IPv6 hosts access to IPv4 services, dynamic NAT-PT (Network Address Translation-Protocol Translation) is the appropriate choice.

Common mistakes.

• A. Stateless NAT66 is a mechanism for translating between IPv6 addresses (e.g., for renumbering), but it does not perform protocol translation between IPv6 and IPv4.
• B. Stateful NAT66 is similar to stateless NAT66 in that it translates between IPv6 addresses and maintains state, but it does not perform protocol translation between IPv6 and IPv4.
• D. Static NAT-PT provides a one-to-one, fixed mapping between an IPv6 address and an IPv4 address, which is inefficient and quickly exhausts IPv4 address space when many IPv6 hosts need to access IPv4 services, as each host would require a dedicated IPv4 address.

Concept tested. IPv6 to IPv4 transition mechanisms, NAT-PT

Reference. https://www.cisco.com/c/en/us/td/docs/ios/ipv6/configuration/guide/ipv6_nat_pt_cfg_guide_cisco_ios_xe.html

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