Example: Connecting Logical Systems Within the Same Router Using Logical Tunnel Interfaces

Requirements

On M Series and T Series routers, you can create a logical tunnel interface if you have a Tunnel Services PIC installed on an Enhanced FPC in your routing platform.

On M40e routers, you can create a logical tunnel interface if you have a Tunnel Services PIC. (An Enhanced FPC is not required.)

On an M7i router, logical tunnel interfaces can be created by using the integrated Adaptive Services Module.

On an MX Series router, the master administrator can configure logical tunnel interfaces by including the tunnel-services statement at the [edit chassis fpc slot-number pic number] hierarchy level.

Overview

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. Logical tunnel interfaces behave like regular interfaces. You can configure them with Ethernet, Frame Relay, or another encapsulation type. You can also configure routing protocols across them. In effect, the logical tunnel (lt) interfaces connect two logical systems within the same router. The two logical systems do not share routing tables. This means that you can run dynamic routing protocols between different logical systems within the same router.

You must treat each interface like a point-to-point connection because you can only connect one logical tunnel interface to another at any given time. Also, you must select an interface encapsulation type, configure a corresponding protocol family, and set the logical interface unit number of the peering lt interface.

In this example, the logical tunnel interfaces are configured to behave as Ethernet interfaces with the encapsulation ethernet statement. The IS-IS Protocol is enabled on the logical tunnel interfaces with the family iso statement.

When configuring logical tunnel interfaces, note the following:

• The peering logical interfaces must have the same physical lt interface name. For example, a logical unit on lt-0/1/0 cannot peer with a logical unit on lt-0/0/10. The FPC, PIC, and port numbers must match.
• The peering logical interfaces must be derived from the same PIC or 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.
• 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.

Figure 1 shows the topology used in this example.

Figure 1: Connecting Two Logical Systems

Configuration

CLI Quick Configuration

To quickly connect logical system interfaces, copy the following commands into a text file, remove any line breaks, and then paste the commands into the CLI.

Step-by-Step Procedure

To connect logical system interfaces:

1. Run the show interfaces terse command to verify that the router has a logical tunnel (lt) interface.
   user@host> show interfaces terse

   Interface               Admin Link Proto    Local                 Remote
   so-0/0/0                up    down
   so-0/0/1                up    down
   so-0/0/2                up    down
   so-0/0/3                up    down
   gr-0/1/0                up    up  
   ip-0/1/0                up    up  
   lt-0/1/0                up    up  
   ...

2. Configure the logical tunnel interface on Logical System LS1.

   [edit]user@host# set logical-systems LS1 interfaces lt-0/1/0 unit 0 description LS1->LS2 user@host# set logical-systems LS1 interfaces lt-0/1/0 unit 0 encapsulation ethernet user@host# set logical-systems LS1 interfaces lt-0/1/0 unit 0 peer-unit 1 user@host# set logical-systems LS1 interfaces lt-0/1/0 unit 0 family inet address 10.0.8.13/30 user@host# set logical-systems LS1 interfaces lt-0/1/0 unit 0 family iso

3. Configure the logical tunnel interface on Logical System LS2.

   [edit]user@host# set logical-systems LS2 interfaces lt-0/1/0 unit 1 description LS2->LS1 user@host# set logical-systems LS2 interfaces lt-0/1/0 unit 1 encapsulation ethernet user@host# set logical-systems LS2 interfaces lt-0/1/0 unit 1 peer-unit 0 user@host# set logical-systems LS2 interfaces lt-0/1/0 unit 1 family inet address 10.0.8.14/30 user@host# set logical-systems LS2 interfaces lt-0/1/0 unit 1 family iso

4. If you are done configuring the device, commit the configuration.

   [edit]user@host# commit

Verification

Confirm that the configuration is working properly.

• Verifying That the Logical Systems Are Up
• Verifying Connectivity Between the Logical Systems

Verifying That the Logical Systems Are Up

Purpose

Make sure that the interfaces are properly configured.

Action

Interface               Admin Link Proto    Local                 Remote
so-0/0/0                up    down
so-0/0/1                up    down
so-0/0/2                up    down
so-0/0/3                up    down
gr-0/1/0                up    up  
ip-0/1/0                up    up  
lt-0/1/0                up    up  
lt-0/1/0.0              up    up   inet     10.0.8.13/30    
                                   iso     
lt-0/1/0.1              up    up   inet     10.0.8.14/30    
                                   iso  
...

Verifying Connectivity Between the Logical Systems

Purpose

Make sure that the network address appears as directly connected.

Action

logical-system: LS1

inet.0: 2 destinations, 2 routes (2 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

10.0.8.12/30       *[Direct/0] 00:00:34
                    > via lt-0/1/0.0
10.0.8.13/32       *[Local/0] 00:00:34
                      Local via lt-0/1/0.0
-----
 
logical-system: LS2

inet.0: 2 destinations, 2 routes (2 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

10.0.8.12/30       *[Direct/0] 00:00:34
                    > via lt-0/1/0.1
10.0.8.14/32       *[Local/0] 00:00:34
                      Local via lt-0/1/0.1
...