Figure 5-5 Parameter Problem message in Objective-C

Printer QR Code in Objective-C Figure 5-5 Parameter Problem message

Unrecognized Next Header: A Next Header is unrecognized for the IPv6 implementation present on the node Unrecognized IPv6 option: The packet holds an unrecognized option (see Section 322) for the IPv6 implementation present on the node

A second type of ICMP message is the informational message These messages are subdivided into three groups: diagnostic messages, messages for the management of multicast groups, and Neighbor Discovery messages

The Echo Request message and its corresponding Echo Reply message are ICMP diagnostic messages In particular, these two messages are used to implement the ping diagnostic application that allows us to test whether a destination is reachable The format of these two messages is the same, as illustrated in Figure 5-6 The IPv6 destination address can be any valid IPv6 address The Type field has value 129 The Code field has value zero The Identifier field is an identifier used to set a relationship between Echo Request and Echo Reply messages It can also be set to zero The Sequence Number field is a sequence number used to set a relationship between Echo Request and Echo Reply messages It can also be set to zero The Data field contains zero or more octets of data arbitrarily generated by the diagnostic procedure

Every IPv6 node must implement an ICMP Echo reply function that receives Echo requests and sends corresponding Echo replies, whose format is illustrated in Figure 5-6 The IPv6 destination address is set equal to the IPv6 source address of the Echo Request message The Type field has value 129 The Code field has value zero The Identifier field is copied from the field of the same name in the Echo Request message The Sequence Number field is copied from the field of the same name in the Echo Request message The Data field is copied from the field of the same name in the Echo Request message An example of this type of packet is shown in Section B2 in Appendix B

ICMP Group Membership messages are used to convey information about multicast group membership from nodes to their neighboring routers (connected on the same link) Their format is illustrated in Figure 5-7 The IPv6 destination address values change in function for the different types of messages: In a Group Membership Query message, the destination address is equal to the multicast address of the group being queried or equal to the link local All-Nodes (FF02::1, see Section 481) multicast address In a Group Membership Report or Group Membership Reduction message, the destination address is equal to the multicast address of the group being reported or terminated

The IPv6 header Hop Limit field is set to 1 (packets are exchanged only between adjacent nodes) The Type field assumes values 130 (Group Membership Query), 131 (Group Membership Report), or 132 (Group Membership Reduction) The Code field has value zero The Maximum Response Delay field expresses a value in milliseconds In Group Membership Query messages, this field indicates the maximum time that the responding Report messages can be delayed In Group Membership Report or Group Membership Reduction messages, this field is initialized to zero by the sender and ignored by the receiver The Unused field is unused and must be initialized to zero by the sender and ignored by the receiver

ICMP messages that will be introduced from this point to the end of the chapter are messages of Neighbor Discovery type (specified by RFC 19706) We discussed the need and use of these types of messages in Section 28 In this section, we will analyze formats of different messages in more detail IPv6 nodes transmit Router Solicitation messages (see Figure 5-8) to prompt routers to generate Router Advertisements immediately