4A0-D01 practice question 9 of 10

Which of the following statements about IP-VRFs in Nokia’s SR Linux is FALSE?

Full set: 35 questions
Answer options
A: An IP-VRF is a Layer 3 network instance.
B: Packets in an IP-VRF are forwarded based on the destination IP address.
C: The router maintains a distinct route table for each IP-VRF instance.
D: Multiple servers can be connected to the same subnet in an IP-VRF. Correct answer
Correct Answer:
D. Multiple servers can be connected to the same subnet in an IP-VRF.
Explanation

An IP-VRF is a purely Layer 3 construct, equivalent to a virtual router. It contains an independent routing table and a set of Layer 3 interfaces. A subnet, where multiple servers can communicate directly, is a Layer 2 broadcast domain. While this Layer 2 domain is linked to an IP-VRF via a Layer 3 interface (such as an Integrated Routing and Bridging - IRB - interface) which acts as the default gateway, the servers themselves are not connected within the Layer 3 IP-VRF. They are connected to a Layer 2 network (like a mac-vrf or VLAN) that is merely associated with the IP-VRF. Therefore, the statement is technically false.

Why Incorrect

A. An IP-VRF is explicitly defined in Nokia SR Linux documentation as a Layer 3 network instance, or virtual router, for traffic isolation.
B. The fundamental principle of IP routing, which is the function of an IP-VRF, is to forward packets based on the destination IP address in the packet header.
C. The core purpose and defining characteristic of a VRF is to create an isolated routing domain with its own distinct routing and forwarding table.

References

1. Nokia SR Linux R22.10.1 System Management Guide, Section: "Network instances": This document states, "SR Linux supports different types of network instances for Layer-2 and Layer-3 traffic isolation... An ip-vrf network instance is a virtual router for Layer-3 traffic." This confirms that an IP-VRF is a Layer 3 instance (A is true) and that it provides isolation, which is achieved through distinct tables (C is true). The document also defines a mac-vrf as a "virtual switch for Layer-2 traffic," highlighting the separation between L2 and L3 domains, which supports the reasoning for D being false.

2. Nokia SR Linux R22.10.1 Layer 3 Services Guide, Section: "Unicast routing overview": This guide details the IP forwarding process. It implicitly confirms that within any routing context, including an IP-VRF, the forwarding decision is based on a lookup of the destination IP address in the Forwarding Information Base (FIB). This makes statement B true.

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