Setting IP Interface Properties

This section explains how to use the ipadm command to set selected IP interface properties.

IP interfaces, like datalinks, have properties that you can customize for your specific network environment. For each interface, two sets of properties exist, one set for the IPv4 and the other set for the IPv6 protocols. Some properties, such as MTU, are common to both datalinks and IP interfaces. Thus, you can have one MTU value for a datalink and a different MTU value for the interface configured over that link. Further, you can have different MTU values that apply to IPv4 and IPv6 packets that traverse that IP interface.

Three ipadm subcommands are used to set IP interface properties:

The ipadm show-ifprop -p property interface subcommand displays the properties of an IP interface and their current values. If you do not use the -p property option, then all the properties of the IP interface are listed. If you do not specify an IP interface, then all the properties of all IP interfaces are listed.
The ipadm set-ifprop -p property=value interface subcommand assigns a value to the IP interface's property.
The ipadm reset-ifprop -p property interface subcommand resets the specific property to its default values.

Enabling Packet Forwarding

In a network, a host can receive data packets that are destined for another host system. By enabling packet forwarding in the receiving local system, that system can forward the data packet to the destination host. By default, IP forwarding is disabled.

Packet forwarding is managed by a property that can be set on both IP interfaces and on the TCP/IP protocol. If you want to be selective in how packets are forwarded, then you enable packet forwarding on the IP interface. For example, you might have a system that has multiple NICs. Some NICs are connected to the external network, while other NICs are connected to the private network. You would therefore enable packet forwarding only on some of the interfaces, rather than on all interfaces.

You can also enable packet forwarding globally on the system by setting the property of the TCP/IP protocol. See Enabling Packet Forwarding Globally.

Note - The forwarding property of either IP interfaces or protocols is not exclusive. You can set the property for the interface and the protocol at the same time. For example, you could enable packet forwarding globally on the protocol, and then customize packet forwarding for each IP interface on the system. Thus, although enabled globally, packet forwarding can still be selective for the system.

To enable packet forwarding on the IP interface, use the following command:

# ipadm set-ifprop forwarding=on [-m protocol-version] interface

where protocol-version is either IPv4 or IPv6. You must issue the command separately for IPv4 and IPv6 packets.

The following is an example of how you might enable only IPv4 packet forwarding on your system:

# ipadm show-ifprop -p forwarding net0
IFNAME   PROPERTY     PROTO   PERM   CURRENT   PERSISTENT   DEFAULT   POSSIBLE
net0     forwarding   ipv4    rw     off       off          off       on,off
net0     forwarding   ipv6    rw     off       --           off       on,off

# ipadm set-ifprop -p forwarding=on -m ipv4 net0
# ipadm show-ifprop net0
IFNAME   PROPERTY         PROTO  PERM  CURRENT  PERSISTENT  DEFAULT   POSSIBLE
...
net0     forwarding       ipv4   rw    on       on          off       on,off
...

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