ipv6 pathmtu
Function
The ipv6 pathmtu command sets the PMTU for a specified destination IPv6 address.
The undo ipv6 pathmtu command deletes the PMTU for a specified destination IPv6 address.
By default, the PMTU for a specified destination IPv6 address is not set.
Parameters
| Parameter | Description | Value |
|---|---|---|
| ipv6-address | Specifies the IPv6 address for which a PMTU is to be set. | The value consists of 128 octets, which are classified into 8 groups. Each group contains 4 hexadecimal numbers in the format X:X:X:X:X:X:X:X. |
| path-mtu | Specifies the path MTU, that is, the maximum size of IPv6 packets allowed to be sent along the path. | The value is an integer that ranges from 1280 to 10000, in bytes. The default value is 1500, which is recommended. |
Usage Guidelines
Usage Scenario
A PMTU is used to determine the proper size of packets to be transmitted along the path from a source to a destination. Usually, a device fragments and forwards packets based on the dynamically learnt PMTU. Packets that are sent using this PMTU do not need to be fragmented during transmission. This reduces pressure on routing devices and optimizes network resource utilization to obtain the maximum throughput.
In some special cases, however, to protect devices on the network and avoid large-size 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.
Precautions
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 can use the default PMTU value instead of running the ipv6 pathmtu command to set a static PMTU.
The priorities of the static PMTU, dynamic PMTU, and default PMTU of the system are in a descending order.
