pmtu Command

Purpose

Displays and deletes Path MTU discovery related information.

Syntax

pmtu [-inet6] display/[delete [-dst destination] [-gw gateway] ]

Description

The pmtu command is provided to manage the Path MTU information. The command can be used to display the Path MTU table. By default the Ipv4 pmtu entries are displayed. Ipv6 pmtu entries can be displayed using the –inet6 flag. This command also enables a root user to delete a pmtu entry with the pmtu delete command. The delete can be based on destination, gateway, or both.

A pmtu entry gets added into the PMTU table when a route add occurs with an MTU value.

A network option, pmtu_expire, is provided to expire unused pmtu entries. The default value of pmtu_expire is 10 minutes.

Flags

Item	Description
-dst	Specifies the destination of the pmtu entry to be deleted.
-gw	Specifies the gateway of the pmtu entry to be deleted.
-inet6	Specifies to display or delete Ipv6 pmtu entry.

Exit Status

Item	Description
0	The command completed successfully.
1	An error occurred.

Security

Attention RBAC users and Trusted AIX® users: This command can perform privileged operations. Only privileged users can run privileged operations. For more information about authorizations and privileges, see Privileged Command Database in Security. For a list of privileges and the authorizations associated with this command, see the lssecattr command or the getcmdattr subcommand.

Examples

To display Ipv4 pmtu entries, type:
```
pmtu display
```
The output will look similar to the following:
```
dst           gw                If    pmtu     refcnt   redisc_t    exp

 ----------------------------------------------------------------------

192.168.5.5   192.168.10.33    en2    1500        1          0       0
```
The reference count signifies the number of current TCP and UDP applications using this pmtu entry.

The redisc_t entry signifies the amount of time that is elapsed since the last Path MTU discovery attempt. The PMTU is rediscovered after every pmtu_rediscover_interval minutes. Its default value is 30 minutes and can be changed using the no command.

The PMTU entry expiry is controlled by the network option pmtu_expire. Its default value is 10 minutes. This value can be changed using the no command. A value of 0 does not expire any entries. The exp entry signifies the expiry time. PMTU entries having more than zero refcnt have exp of 0. When the refcnt becomes zero, the exp time increases every minute and the entry gets deleted when the exp variable becomes equal to pmtu_expire.
To delete an entry based on destination, type:
```
pmtu delete -dst 192.168.5.5 
```

To display Ipv6 , type:

pmtu -inet6 display

Output will look similar to the following:

dst                       gw      If    pmtu     refcnt   redisc_t   exp

 -----------------------------------------------------------------------

fe80::204:acff:fee4:ab3b  ::    lo0   16896        2          2        0

Location

/usr/sbin/pmtu

Files

Item	Description
/usr/sbin/pmtu	Contains the pmtu command.