The root bridge in a spanning-tree network is the bridge with the smallest or the lowest bridge ID.

In the absence of a manually configured priority, the Spanning Tree Protocol (STP) elects the root bridge based on the lowest bridge ID, which is a combination of the priority and the MAC address. The device with the lowest MAC address will have the lowest bridge ID and thus be elected as the root bridge.

References

• Juniper Networks Technical Documentation on STP

To ensure that MPLS traffic-engineered routes are used without affecting IGP routes in the route tables, the mpls-forwarding traffic engineering setting should be used. This setting allows MPLS to influence forwarding without changing the IGP route selection.References:

• MPLS Traffic Engineering, Juniper Networks Documentation
• Traffic Engineering and LSP Optimization, Juniper Networks Documentation

To create connections between routing instances on the same Junos device and route between them, you can use logical tunnel interfaces, which are virtual interfaces that can be used to route traffic between instances without the need for physical connectivity. Additionally, loopback interfaces, which represent the device itself, can be used to route traffic between routing instances as they are always up and can be reached within the device.

References

• Juniper Networks Technical Documentation on Routing Instances
• Juniper Networks Technical Documentation on Logical Tunnel Interfaces