The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Internet Layer (OSI Network Layer) Protocols            9  Internet Control Message Protocol (ICMP/ICMPv4 and ICMPv6)                 9  ICMP Message Types and Formats

ICMPv4 Traceroute Messages 1 ICMPv6 Destination Unreachable Messages

The original ICMP defines for version 4 of the Internet Protocol (IPv4) a number of error messages to allow communication of problems on an internetwork. When IP version 6 (IPv6) was developed, the differences between IPv4 and IPv6 were significant enough that a new version of ICMP was also required: the Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6), currently specified in RFC 2463. Like ICMPv4, ICMPv6 defines several error messages that let a source be informed when something goes wrong.

In this section I describe the four ICMPv6 error messages defined in RFC 2463. I first discuss ICMPv6 Destination Unreachable messages, used to tell a device a datagram it sent could not be delivered for a variety of reasons. I describe Packet Too Big error messages, which are sent when a datagram can't be sent due to being too large for an underlying network it needs to traverse. I explain the use of Time Exceeded messages, which indicate that too much time was taken to accomplish a transmission. I conclude with a look at messages, which provide a generalized way of reporting errors not described by any of the preceding ICMPv6 error message types.

ICMPv4 Traceroute Messages 1 ICMPv6 Destination Unreachable Messages