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.
ipv6 pathmtu ipv6-address [ vpn-instance vpn-instance-name ] [ path-mtu ]
undo ipv6 pathmtu ipv6-address [ vpn-instance vpn-instance-name ]
| Parameter | Description | Value |
|---|---|---|
| ipv6-address | Specifies the IPv6 address for which a PMTU is to be set. NOTE:
The link-local address does not take effect. |
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. |
| vpn-instance vpn-instance-name | Specifies the name of an IPv6 VPN instance for which a PMTU is to be set. |
The value must be an existing VPN instance name. |
| 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 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 recommend 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.