The provided configuration sets the bridge priority for MSTI 1 to 4k (4096) and for MSTI 2 to 8k (8192). In MSTP, the switch with the lowest bridge priority becomes the root bridge for that instance. The default priority is 32768.

With a priority of 4k, Switch1 will have a lower priority than other switches (assuming they have default or higher priorities) for MSTI 1, making it the root bridge for VLANs 10 and 20.

For load balancing, another switch (e.g., Switch2) would be configured as the root for MSTI 2 (with a priority < 8k). If that switch fails, Switch1, with the next-lowest priority of 8k, will be elected as the new root for MSTI 2, thus becoming the root for both instances.

B. Switch1 will be the root bridge for msti 2.

This is incorrect because, in a load-balancing design, another switch would be configured with a lower priority (e.g., 4k) to be the root for MSTI 2.

C. Switch 1 will not assume the role of root bridge for both mstil and msti2 if Switch2 goes down.

This is incorrect. If the primary root for MSTI 2 fails, Switch1's priority of 8k is the next best, causing it to become the root for MSTI 2.

1. Juniper Networks TechLibrary, Junos OS Documentation, "Understanding MSTP": This document explains that the switch with the lowest bridge ID (which includes priority) becomes the root bridge for an MSTI. The default priority is 32,768. The configured priority of 4096 (4k) for MSTI 1 makes Switch1 the root.

2. Juniper Networks TechLibrary, Junos OS Documentation, "Example: Configuring MSTP for VLAN Load Balancing on EX Series Switches": This configuration example demonstrates a typical load-balancing scenario. One switch is configured with a low priority (e.g., 4096) for one MSTI and a higher priority (e.g., 8192) for a second MSTI. A second switch is configured with the priorities reversed. This confirms the design intent and the failover behavior where the switch with the 8192 priority acts as the backup root and takes over if the primary root fails.

3. Juniper Networks TechLibrary, Junos OS Documentation, bridge-priority (MSTP): This page details the bridge-priority statement within the [edit protocols mstp msti] hierarchy. It confirms that the range is 0 through 61440 in increments of 4096, and a lower value increases the likelihood of becoming the root bridge. This supports the analysis that 4k is a root priority and 8k is a backup root priority.