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Cisco Self-Study: Implementing IPv6 Networks (IPV6) by Régis Desmeules

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Path MTU Discovery (PMTUD) for IPv6

As described in RFC 1191, the path MTU discovery (PMTUD) mechanism was defined for IPv4 in 1990; it is not new to the IPv6 protocol. However, in IPv4 PMTUD is optional and is not commonly used by nodes.

The main goal of PMTUD is finding out the MTU value along a path when a packet is sent to a destination to avoid fragmentation. Then the source node can use the maximum MTU size found to communicate with the destination node. Fragmentation may occur in intermediary routers when the packet is larger than the link layer's MTU. Fragmentation is a harmful and costly operation in terms of CPU cycles for routers. Moreover, in some circumstances, fragmentation over fragmentation might occur in several intermediate ...

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