300-410 Question #42: Real Exam Question with Answer & Explanation

The correct answer is A: NHRP. The Next Hop Resolution Protocol (NHRP) is essential for mGRE tunnels to dynamically map private IP addresses of spoke routers to their public NBMA (Non-Broadcast Multi-Access) addresses.

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Question

Which protocol is used to determine the NBMA address on the other end of a tunnel when mGRE is used?

Options

ANHRP
BIPsec
CMP-BGP
DOSPF

Explanation

The Next Hop Resolution Protocol (NHRP) is essential for mGRE tunnels to dynamically map private IP addresses of spoke routers to their public NBMA (Non-Broadcast Multi-Access) addresses.

Common mistakes.

B. IPsec is a suite of protocols used for secure communication (authentication, encryption) over an IP network, but it is not used for NBMA address resolution in mGRE.
C. MP-BGP (Multiprotocol BGP) is an extension of BGP that carries routing information for multiple network layer protocols, including VPNv4 for MPLS VPNs, but it's a routing protocol, not an NBMA address resolution protocol.
D. OSPF (Open Shortest Path First) is an interior gateway routing protocol (IGP) that establishes and maintains routing tables, but it does not perform NBMA address resolution for mGRE tunnels.

Concept tested. mGRE NHRP address resolution

Reference. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/sec_conn_dmvpn/configuration/xe-3s/sec-dmvpn-xe-3s-book/config-dmvpn.html

Topics

#NHRP#mGRE#DMVPN#NBMA

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