Configuring a PMTU

This section describes now to set a path maximum transmission unit (PMTU) on an interface. This setting enables a device to send packets based on proper MTUs across a network. This helps prevent packet fragmentation, reduce the burden of the devices, and efficiently use network resources.

Setting an IPv6 MTU on an interface

Context

The MTU on an interface determines whether IP packets on the interface need to be fragmented.

The default value of the MTU on an interface varies with the interface type.

Access the system view.
```
system-view
```

Access the interface view.

interface interface-type interface-number

Set the IPv6 MTU on the interface.
```
ipv6 mtu mtu
```

Follow-up Procedure

If the IPv6 MTU value is changed, run the shutdown command and the undo shutdown command in the interface view to make the configuration take effect.

Run the display ipv6 interface command to view the current IPv6 MTU on the interface.

<sysname> display ipv6 interface GigabitEthernet 0/0/1
GigabitEthernet0/0/1 current state : UP                                         
IPv6 protocol current state : UP                                                
IPv6 is enabled, link-local address is FE80::222:A1FF:FE00:2259                 
  Global unicast address(es):                                                   
    2001:1::1:1, subnet is 2001:1::/64                                          
  Joined group address(es):                                                     
    FF02::1:FF01:1                                                              
    FF02::1:FF00:2259                                                           
    FF02::2                                                                     
    FF02::1                                                                     
  MTU is 1500 bytes                                                             
  ND DAD is enabled, number of DAD attempts: 1                                  
  ND reachable time is 30000 milliseconds                                       
  ND retransmit interval is 1000 milliseconds                                   
  Hosts use stateless autoconfig for addresses

Creating Static PMTU Entries

Context

Static PMTU entries are manually configured and do not age.

Access the system view.
```
system-view
```
Set the PMTU value of a specified IPv6 address.
```
ipv6 pathmtu ipv6-address [ path-mtu ]
```
By default, the PMTU of an IPv6 address is 1500 bytes.

Follow-up Procedure

Run the display ipv6 pathmtu static command to view information about static PMTU entries.

<sysname> display ipv6 pathmtu static
IPv6 Destination Address                ZoneID PathMTU LifeTime(M) Type    FF 
2001:1::1:2                              0       1500     -        Static  No
------------------------------------------------------------------------------- 
Static: 1

Configuring the PMTU Aging Time

Context

The PMTU aging time is used to change the lifetime of a PMTU entry in the cache.

Access the system view.
```
system-view
```
Set the PMTU aging time.
```
ipv6 pathmtu age age-time
```
By default, the dynamic PMTU aging time is 10 minutes.

Follow-up Procedure

Run the display ipv6 pathmtu dynamic command to view information about the dynamic PMTU entries.

<sysname> display ipv6 pathmtu dynamic
IPv6 Destination Address                 ZoneID  PathMTU  LifeTime(M)  Type      FF 
fe80::12                                 0       1300     40           Dynamic   YES
------------------------------------------------------------------------------- 
Total: 1      Dynamic: 1     Static: 0