Parameter Problem

A router or the destination sends an ICMPv6 Parameter Problem message when there is an error in the IPv6 header or an extension header that prevents IPv6 from performing additional processing. Figure 5-5 shows the structure of the Parameter Problem message.

Figure 5-5 The structure of the Parameter Problem message

In the Parameter Problem message, the Type field is set to 4 and the Code field has a value in the range of 0 through 2. Following the Checksum field is the 32-bit Pointer field that indicates the byte offset (starting at 0) in the IPv6 packet at which the error was encountered. Following the Pointer field is the leading portion of the discarded packet, sized so that the entire ICMPv6 message is no larger than 1280 bytes. The Pointer field value is set to the correct offset even when the location of the error is not within the portion of the discarded packet.

Table 5-2 shows the Code field values for Parameter Problem messages.

Table 5-2 ICMPv6 Parameter Problem Messages

The Parameter Problem-Unrecognized IPv6 Option Encountered message is used when both of the following are true:

■An option in a Hop-by-Hop Options header or a Destination Options header is not recognized.

■Within the option’s Option Type field, the two high-order bits are set to either 10 (binary) or 11 (binary).

For more information about the Option Type field, see the “Hop-by-Hop Options Header” section in Chapter 4.