Operation Manual – IPv6H3C S3610&S5510 Series Ethernet Switches Chapter 1 IPv6 Basics Configuration1-10Note:z In addition to an address prefix, the prefix information option also contains thepreferred lifetime and valid lifetime of the address prefix. After receiving a periodicRA message, the node updates the preferred lifetime and valid lifetime of theaddress prefix accordingly.z An automatically generated address is applicable within the valid lifetime and will beremoved when the valid lifetime times out.V. RedirectionWhen a host is started, its routing table may contain only the default route to thegateway. When certain conditions are satisfied, the gateway sends an ICMPv6 redirectmessage to the source host so that the host can select a better next hop to forwardpackets (similar to the ICMP redirection function in IPv4).The gateway will send an IPv6 ICMP redirect message when the following conditionsare satisfied:z The receiving interface is the forwarding interface.z The selected route itself is not created or modified by an IPv6 ICMP redirectmessage.z The selected route is not the default route.z The forwarded IPv6 packet does not contain any routing header.1.1.4 IPv6 PMTU DiscoveryThe links that a packet passes from the source to the destination may have differentMTUs. In IPv6, when the packet size exceeds the link MTU, the packet will befragmented at the source end so as to reduce the processing pressure of theforwarding device and utilize network resources rationally.The path MTU (PMTU) discovery mechanism is to find the minimum MTU of all links inthe path from the source to the destination. Figure 1-5 shows the working procedure ofthe PMTU discovery.
