In practical IPv6 deployments, encapsulating IPv6 packets inside IPv4 packets so they can cross an IPv4 network is known as what?

Introduction / Context:
During the transition from IPv4 to IPv6, many networks must carry IPv6 traffic over existing IPv4 infrastructure. One common way to accomplish this is to encapsulate IPv6 packets inside IPv4 packets, allowing them to traverse IPv4-only segments without modification to the core network. Understanding the name and purpose of this technique is important for network design and certification exams.

Given Data / Assumptions:

• We have both IPv4 and IPv6 networks in the overall topology.
• Some intermediate networks support only IPv4.
• IPv6 packets need to cross these IPv4-only sections.
• The question asks for the term used when IPv6 is encapsulated in IPv4.

Concept / Approach:
Encapsulating one protocol inside another for transport across an incompatible network is referred to as tunneling. In the context of IPv6, tunneling methods such as 6to4 or manually configured tunnels wrap IPv6 packets inside IPv4 headers. The outer IPv4 header provides addressing across the IPv4 network, while the inner IPv6 packet is delivered unchanged once the tunnel is terminated. This is distinct from routing, which simply forwards packets, and from NAT, which modifies addresses.

Step-by-Step Solution:
1. Identify the problem: IPv6 packets must travel across an IPv4-only network.2. Recognize that the solution is to place the IPv6 packet inside an IPv4 packet.3. This process of encapsulating one protocol packet inside another is known as tunneling.4. The tunnel endpoints add and remove the outer IPv4 header.5. Therefore, the correct term for this method is tunneling.

Verification / Alternative check:
IPv6 transition documents and RFCs describe several tunneling mechanisms that use this principle. Examples include manually configured tunnels, 6to4, and ISATAP. These all rely on encapsulating IPv6 inside IPv4, which clearly matches the definition of a tunnel rather than simple routing or address translation.

Why Other Options Are Wrong:
Option B, hashing, refers to generating a fixed-size value from input data, often used in security or load balancing, not in this encapsulation context. Option C, routing, describes the generic process of forwarding packets based on destination addresses without encapsulating another protocol inside. Option D, Network Address Translation, modifies addresses and sometimes ports but does not describe the process of wrapping IPv6 inside IPv4 packets end to end.

Common Pitfalls:
Students sometimes confuse tunneling with NAT because both appear in transition scenarios. However, tunneling preserves the original packet unchanged inside an outer header, while NAT alters address information. Another mistake is thinking that routing by itself can overcome protocol incompatibility; in reality, encapsulation is needed when the core cannot understand the inner protocol.

Final Answer:
Tunneling