Before you can connect logical systems to each other you need to enable tunnel services on the Juniper vMX chassis and create the logical tunnel interfaces that act as the links between your virtual routers. This video covers exactly how to do that.

Logical systems don’t connect to each other using physical interfaces — they use logical tunnel interfaces, which appear in the CLI as LT000.x where x is the unit number you assign. These interfaces are what allow traffic to pass from one virtual router to another within the same physical device, and they behave exactly like normal Ethernet interfaces from a routing protocol perspective.

Before logical tunnel interfaces are available you first need to enable tunnel services on the chassis. This is done under the chassis FPC configuration hierarchy using set chassis fpc 0 pic 0 tunnel-services. Without this step the LT interfaces simply won’t exist and you won’t be able to create the inter-logical-system connections the rest of the series depends on.

Once tunnel services are enabled we verify the LT interface is present using show interfaces terse and match LT, confirming the lt-0/0/0 interface is now available for sub-interfacing. From there we walk through the naming convention used throughout the series — where the unit number reflects the source and destination routers to make identification easier. For example, unit 12 connects router 1 to router 2, unit 21 is the return path, unit 34 connects router 3 to router 4, and so on.

Understanding this naming convention from the start makes the rest of the series significantly easier to follow. The interface naming is deliberate — when you’re deep in a configuration and need to know which logical tunnel connects which pair of routers, the unit number tells you immediately.

This is the foundation that everything else in the series builds on. Get the tunnel services enabled and understand the LT interface structure before moving on to the configuration work in the next videos.