Which statement about a virtual-router type of routing instance is correct?

The primary function of a virtual-router routing instance in Junos OS is to create a separate and isolated routing table (e.g., instance-name.inet.0) and a corresponding forwarding table. This effectively partitions a single physical router into multiple independent logical routers. Each virtual-router instance has its own interfaces, routing protocol configurations, and policies, operating independently from the main inet.0 routing table and other instances. This is used for non-VPN network segmentation scenarios where traffic from different logical networks must be kept separate.

A. This is a general goal of network segmentation, which routing instances facilitate, but it does not describe the specific mechanism of a virtual-router instance.

B. This is incorrect. Junos OS supports multiple routing instance types, including vrf, forwarding, l2vpn, and vpls, among others.

C. The vrf (Virtual Routing and Forwarding) instance type is specifically used for Layer 3 VPN implementations, as it includes necessary BGP policies like route targets.

1. Juniper Networks TechLibrary, Junos OS Routing Protocols Library for Routing Devices, "Routing Instances Overview."

Section: "Routing Instance Types"

Content: This document explicitly states for the virtual-router type: "In this type of instance, there is a one-to-one mapping between an interface and a routing instance. Each virtual-router instance has its own routing and forwarding tables." This directly supports the correct answer (D). It also describes the vrf type as being used for Layer 3 VPNs, invalidating option C. The list of multiple instance types in this document invalidates option B.

2. Juniper Networks TechLibrary, Junos OS Routing Protocols Library for Routing Devices, "Example: Configuring a Virtual Router Routing Instance."

Section: "Overview"

Content: The overview explains that a virtual router instance "isolates traffic" and "has its own routing table." This reinforces that the core function is the creation of separate routing and forwarding planes.

3. Juniper Networks Day One Library, "This Week: An Introduction to Logical Systems and Virtual Routers."

Section: "Virtual Routers"

Content: This guide details that a virtual router "creates a separate routing and forwarding table" and is a method of partitioning a device into multiple, independent, logical routers for non-VPN scenarios. This confirms the purpose described in option D.