Usage Scenario
A Path Maximum Transmission Unit (PMTU) is used to determine the proper size of packets to be transmitted along the path from a source to a destination. Commonly, a device fragments and forwards packets based on the dynamic PMTU learning function of the system, trying not to fragment packets during transmission. In this manner, loads on intermediate Routers are reduced and effective network resource use.
In some special cases, however, to protect devices on the network and avoid the large-sized packet attacks, you can run the
ipv6 pathmtu command to set a static PMTU for the specified destination IPv6 address to control the maximum size of packets that can be transmitted between the source and the destination.
Configuration Impact
On the path along which packets are transmitted, a node discards the received packets if its MTU is smaller than the PMTU of the received packets. Therefore, in most cases, dynamic PMTU learning is recommended unless there are security vulnerabilities on the network. You do not need to run the ipv6 pathmtu command to set a static PMTU, that is, use the default PMTU.
Precautions
The priorities of the static PMTU, dynamic PMTU, and default PMTU of the system are in a descending order.