4A0-115 practice question 8 of 10

A Layer-3 EVPN service is configured to use the interface-ful unnumbered forwarding model. Which of the following statements is FALSE?

Full set: 40 questions
Answer options
A: Each participating PE advertises a MAC/IP route that carries the MAC address of SBD IRB interface.
B: IP-Prefix routes exchanged between PES include a non-zero MAC address as an overlay index. Correct answer
C: The VPRN service is configured to allow the advertisement of IP prefixes.
D: The SBD IRB interface configured in the VPRN service has no IP address assigned to it.
Correct Answer:
B. IP-Prefix routes exchanged between PES include a non-zero MAC address as an overlay index.
Explanation

In the interface-ful unnumbered forwarding model for Layer-3 EVPN, IP-Prefix routes (EVPN Route Type 5) are advertised with the Gateway IP address field in the NLRI set to 0.0.0.0. The router's MAC address, which is essential for forwarding, is carried in the BGP Router's MAC Extended Community attribute, not directly in the NLRI as a primary field. While the MAC address is used by the receiving PE to forward traffic, referring to it as an "overlay index" can be misleading. The primary overlay index is the VNI (VXLAN Network Identifier), which identifies the forwarding context (the SBD). The statement that the route includes a non-zero MAC address as an overlay index is the most imprecise and therefore considered false in the context of strict terminology where the VNI is the primary index.

Why Incorrect

A. This is a true statement. A Type-2 MAC/IP route is advertised with the SBD IRB's MAC address and a null IP address to enable remote PEs to resolve the gateway MAC for inter-subnet traffic.
C. This is a true statement. For a VPRN to participate in Layer-3 EVPN and exchange subnet reachability, it must be explicitly configured to advertise IP prefixes into the BGP EVPN address family.
D. This is a true statement. The term "unnumbered" in this model's name specifically means that the SBD's Integrated Routing and Bridging (IRB) interface is not configured with its own IP address.

References

1. Nokia 7x50 SR OS Services Guide, Release 22.10.R1, "EVPN for VXLAN in a VPRN service" section, page 161

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