Which of the following is NOT a step in the Header Translation procedure (IPv6…

Concept

Header Translation is the transition technique used at the boundary where an IPv6-only sender must reach an IPv4-only receiver. A translating router rebuilds the packet by mapping each IPv6 header field onto its IPv4 counterpart, dropping IPv6-specific fields that have no IPv4 equivalent, and recomputing values (such as the IPv4 header checksum) that IPv6 never carried.

How the procedure works (field-by-field)

The standard translation steps are:

1. The IPv4-mapped IPv6 address is converted to an IPv4 address by extracting the rightmost 32 bits.

2. The IPv6 priority (traffic-class) field is discarded, because IPv4 handles precedence differently.

3. The IPv6 flow label is ignored – IPv4 has no flow-label field, so there is nothing to map it onto.

4. Compatible IPv6 extension headers are converted into IPv4 options.

5. The IPv4 header-length and total-length fields are computed and inserted.

6. The IPv4 header checksum is calculated and inserted (IPv6 carries no header checksum).

Applying it to this question

Extracting the rightmost 32 bits of the mapped address and discarding the priority field are both genuine steps of the procedure. The flow label, however, is not taken into account during translation – IPv4 has no flow-label field, so the flow label is simply dropped. The statement that the IPv6 flow label is considered therefore describes the one action the procedure does not perform, which is what the question asks for.

Cross-check

• Mapped address → rightmost 32 bits: a genuine translation step (address mapping).

• Priority field discarded: a genuine translation step (no direct IPv4 equivalent).

• Flow label considered: this is the statement that is not part of the procedure, because the flow label is ignored/dropped.