Configuring Logical Tunnel Interfaces

Logical tunnel (lt-) interfaces provide quite different services depending on the host router:

On M Series and T Series routers, logical tunnel interfaces allow you to connect logical systems, virtual routers, or VPN instances. The router must be equipped with a Tunnel Services PIC or an Adaptive Services Module (only available on M7i routers). For more information on the latter applications, see the Junos VPNs Configuration Guide.
On J Series Services Routers, lt- interfaces have a completely different function; they enable you to change class-of-service (CoS) classifications and header bits.

For more information, see the following section or the Junos OS Interfaces and Routing Configuration Guide:

Connecting Logical Systems

Connecting Logical Systems

To connect two logical systems, you configure a logical tunnel interface on both logical systems. Then you configure a peer relationship between the logical tunnel interfaces, thus creating a point-to-point connection.

To configure a point-to-point connection between two logical systems, configure the logical tunnel interface by including the lt-fpc/pic/port statement:

lt-fpc/pic/port {unit logical-unit-number {encapsulation encapsulation;peer-unit unit-number; # peering logical system unit numberdlci dlci-number;family (inet | inet6 | iso | mpls);}}

You can include this statement at the following hierarchy levels:

[edit interfaces]
[edit logical-systems logical-system-name interfaces]

When configuring logical tunnel interfaces, note the following:

You can configure each logical tunnel interface with one of the following encapsulation types: Ethernet, Ethernet circuit cross-connect (CCC), Ethernet VPLS, Frame Relay, Frame Relay CCC, VLAN, VLAN CCC, or VLAN VPLS.
You can configure the IP, IPv6, International Organization for Standardization (ISO), or MPLS protocol family.
The peering logical interfaces must belong to the same logical tunnel interface derived from the Tunnel Services PIC or Adaptive Services Module.
You can configure only one peer unit for each logical interface. For example, unit 0 cannot peer with both unit 1 and unit 2.
To enable the logical tunnel interface, you must configure at least one physical interface statement.
Logical tunnels are not supported with Adaptive Services, Multiservices, or Link Services PICs (but they are supported on the Adaptive Services Module on M7i routers, as noted above).
On M Series routers other than the M40e router, logical tunnel interfaces require an Enhanced Flexible PIC Concentrator (FPC).

For more information about configuring logical systems, see the Junos Routing Protocols Configuration Guide.