Configuring the Interface Address

You assign an address to an interface by specifying the address when configuring the protocol family. For the inet family, configure the interface’s IP address. For the iso family, configure one or more addresses for the loopback interface. For the ccc, tcc, mpls, tnp, and vpls families, you never configure an address.

To assign an address to an interface, include the address statement:

address address {broadcast address;destination address;destination-profile name;eui-64;preferred;primary;}

You can include these statements at the following hierarchy levels:

[edit interfaces interface-name unit logical-unit-number family family]
[edit logical-systems logical-system-name interfaces interface-name unit logical-unit-number family family]

In the address statement, specify the network address of the interface.

For each address, you can optionally configure one or more of the following:

Broadcast address for the interface’s subnet—Specify this in the broadcast statement; this applies only to Ethernet interfaces, such as the management interface fxp0 or em0, the Fast Ethernet interface, and the Gigabit Ethernet interface.
Address of the remote side of the connection (for point-to-point interfaces only)—Specify this in the destination statement.
Assign PPP properties to the remote end—Specify this in the destination-profile statement. You define the profile at the [edit access group-profile name ppp] hierarchy level (for point-to-point interfaces only). For more information, see Configuring IPCP Options.
Whether the router automatically generates the host number portion of interface addresses—The eui-64 statement applies only to interfaces that carry IPv6 traffic, where the prefix length of the address is 64 bits or less, and the low-order 64 bits of the address are zero. This option does not apply to the loopback interface (lo0) because IPv6 addresses configured on the loopback interface must have a 128-bit prefix length.
Whether this address is the preferred address—Each subnet on an interface has a preferred local address. If you configure more than one address on the same subnet, the preferred local address is chosen by default as the source address when you originate packets to destinations on the subnet. For more information about preferred addresses, see Configuring Default, Primary, and Preferred Addresses and Interfaces.
By default, the preferred address is the lowest numbered address on the subnet. To override the default and explicitly configure the preferred address, include the preferred statement when configuring the address.

Whether this address is the primary address—Each interface has a primary local address. If an interface has more than one address, the primary local address is used by default as the source address when you originate packets out the interface where the destination gives no hint about the subnet (for example, some ping commands). For more information about primary addresses, see Configuring Default, Primary, and Preferred Addresses and Interfaces.

By default, the primary address on an interface is the lowest numbered non-127 preferred address on the interface. To override the default and explicitly configure the preferred address, include the primary statement when configuring the address.

Configuring an Interface IPv4 Address

You can configure router interfaces with a 32-bit IPv4 address and optionally with a destination prefix, sometimes called a subnet mask. An IPv4 address utilizes a 4-octet dotted decimal address syntax (for example, 192.16.1.1). An IPv4 address with destination prefix utilizes a 4-octet dotted decimal address syntax appended with a destination prefix (for example, 192.16.1.1/30).

To configure an IPv4 address on JUNOS routers, use the edit interface interface-name unit number family <inet> address a.b.c.d/nn statement at the [edit interfaces] hierarchy level.

Note: Juniper Networks routers support /31 destination prefixes when used in point-to-point Ethernet configurations; however, it is not supported by many other devices, such as hosts, hubs, or routers. You must determine if the peer system also supports /31 destination prefixes before configuration.

Configuring the Interface IPv6 Address

You represent IPv6 addresses in hexadecimal notation using a colon-separated list of 16-bit values.

You assign a 128-bit IPv6 address to an interface by including the address statement:

address aaaa:bbbb:...:zzzz/nn;

You can include this statement at the following hierarchy levels:

[edit interfaces interface-name unit logical-unit-number family inet6]
[edit logical-systems logical-system-name interfaces interface-name unit logical-unit-number family inet6]

The double colon (::) represents all bits set to 0, as shown in the following example:

interfaces fe-0/0/1 {unit 0 {family inet6 {address fec0:1:1:1::2/64;}}}

Note: You must manually configure the router advertisement and advertise the default prefix for autoconfiguration to work on a specific interface.