IPv6 Essentials

Protocol Translation (Chapter 10, RFC 2765)

Table B-13 shows how IPv4 header fields are translated to IPv6 header fields.

Table B-13. Translated IPv6 header fields

Header field	Information
Version	6
Traffic Class	All 8 bits from the Type of Service and Precedence Field are copied.
Flow Label	Zero
Payload Length	The Total Length from the IPv4 header field minus the size of the IPv4 header (including options, if present).
Next Header	Protocol Field copied from IPv4 header.
Hop Limit	TTL value copied from IPv4 header. Since the translator is a router, the value has to be decremented by one (either before or after translation) and the value checked. If zero, an ICMP TTL exceeded message has to be generated.
Source Address	Combination of IPv4-mapped address prefix and the IPv4 address in the 32 low-order bits, for example: ::ffff:0:0:192.168.0.1.
Destination Address	Combination of IPv4-translatable address prefix and the IPv4 destination address, for example: 0::ffff:0:0:0:192.168.0.99.
IPv4 Options	If any IPv4 options are present, they are ignored. If a source route option is present, the packet must be discarded and an ICMPv4 “destination unreachable/source route failed” (Type3, Code 5) error message should be returned to the sender.

Table B-14 shows the header fields when a translated packet needs to be fragmented.

Table B-14. IPv6 header fields with fragmentation

Header field	Information
Header fields
Payload Length	The Total Length from the IPv4 ...