Configuring Static PMTU

Context

Generally, PMTU is dynamically negotiated according to the IPv6 MTU value of an interface. In special situations, to protect devices on the network and avoid attacks from large-sized packets, you can manually configure the PMTU to a specified destination node to control the maximum length of packets forwarded from the device to the destination node.

When the PMTU from the device to a specified destination node is set, the IPv6 MTU values for interfaces on all intermediate devices cannot be smaller than the configured PMTU value. Otherwise, packets are discarded.

Procedure

Run system-view
The system view is displayed.
(Optional) Configure the IPv6 MTU for an interface.
1. Run interface interface-type interface-number
  
  The specified interface view is displayed.
2. (Optional) On an Ethernet interface, run undo portswitch
  
  The interface is switched to Layer 3 mode.
  
  By default, an Ethernet interface works in Layer 2 mode.
  
  Only the S5720-EI, S5720-HI, S5730-HI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6730-H, S6730S-H, S6730-S, and S6730S-S support switching between Layer 2 and Layer 3 modes.
3. Run ipv6 enable
  
  The IPv6 function is enabled on the interface.
  
  By default, the IPv6 function is disabled on an interface.
4. Run ipv6 mtu mtu
  
  The MTU of IPv6 packets on an interface is set.
  
  By default, the MTU of IPv6 packets on an interface is 1500 bytes.
  
  The switch supports MTU setting, so packets sent by the protocol stack are fragmented based on the configured MTU. However, the hardware chip does not support MTU setting, and the default maximum value is 12K.
  
  After the MTU value is changed, run the shutdown and undo shutdown commands or the restart command to restart the interface and allow the changes to take effect.
5. Run quit
  
  Return to the system view.
Run ipv6 pathmtu ipv6-address [ vpn-instance vpn-instance-name ] [ path-mtu ]
The PMTU for a specified IPv6 address is set.

If the parameter path-mtu is not specified, the PMTU for a specified IPv6 address is 1500 bytes.