Configuring Layer 3 Reachability for VLAN Subnets on Juniper MX Series Router

A

The objective of the question is to enable Layer 3 reachability through an MX Series router for the subnets associated with different VLANs. In order to accomplish this, we need to find a solution that allows communication between devices on different VLANs.

A. Gateway IRB interfaces:

The gateway IRB interface is a virtual Layer 3 interface that is associated with a VLAN. This interface can be used to forward traffic between VLANs on the router. It allows the router to act as a default gateway for devices on each VLAN. By configuring IRB interfaces for each VLAN, we can enable communication between devices on different VLANs. This solution is a common way to achieve Layer 3 reachability between VLANs on an MX Series router.

B. BPDU Protect feature:

The BPDU Protect feature is a Layer 2 feature that is used to protect the network against loops. It does not provide Layer 3 reachability between VLANs. This solution is not applicable for this scenario.

C. Layer 2 routing policy:

A Layer 2 routing policy is a policy that is used to forward traffic based on MAC addresses. This policy can be used to direct traffic between VLANs on the router. However, it is not a common solution for Layer 3 reachability. This solution is not applicable for this scenario.

D. Filter-based forwarding:

Filter-based forwarding is a mechanism that is used to forward traffic based on defined criteria, such as source or destination IP address or MAC address. It can be used to direct traffic between VLANs on the router. However, this solution is not as common as using gateway IRB interfaces. It requires more complex configuration and may not be suitable for all scenarios.

Therefore, the correct answer to the question is A. Use gateway IRB interfaces to forward traffic between VLANs.