efix Advertisement See Section 3.7.2 [35] Certification Path Solicitation See Section 3.4.9 [12] Certification Path Advertisement See Section 3.4.9 [12] Experimental mobility protocols For experimental mobility protocols [62] Multicast Router Advertisement See Section 3.2.4 [55] Multicast Router Solicitation See Section 3.2.4 [55] Multicast Router Termination See Section 3.2.4 [55] FMIPv6 Messages See Section 3.7.2 [63] RPL Control Message See Section 3.10.4 [64] Private experimentation Depends on experiment [56] Private experimentation Depends on experiment [56] Reserved for expansion Reserved for the future [56] Deploying IPv6 in 3GPP Networks message indicates what is the MTU of the link that the packet did not fit into. This will help the originator to decrease its Path MTU estimation and hence emit smaller packets (see Section 3.2.3). Time Exceeded A router sends an ICMPv6 Time Exceeded error message when the Hop Limit of the packet reaches zero and hence the packet has to be discarded. The Hop Limit may reach zero, for example, due to misconfiguration errors such as routing loops. The ICMPv6 Time Exceeded message may also be sent when a fragmented packet's reassembly process has timed out. Typically this would happen when one or more frag- ments have been lost in the transit, making the reassembly impossible, but it could also happen when a network is very congested or otherwise too slow to transmit all of the frag- ments. The reassembly timeout typically happens at the receiving node, but could occur in an intermediate router that performs reassembly, for example, for policy control reasons. Parameter Problem In case a router or a destination node is unable to fully parse IPv6 packet or extension headers, the packet will be dropped and an ICMPv6 Parameter Problem message generated. 3.3.2 Informational Messages The ICMPv6 defines two important informational messages for network debugging purposes. These are ICMPv6 Echo Request and Reply for 'pinging' a destination, and ICMPv6 Node Information Query for aski