MGRE Tunneling and NBMA Address Protocol

A.

The protocol that is used to determine the NBMA (Non-Broadcast Multi-Access) address on the other end of a tunnel when mGRE (Multipoint GRE) is used is NHRP (Next Hop Resolution Protocol).

When a packet is sent over an mGRE tunnel, it needs to be addressed to a specific destination. The destination is identified by the NBMA address of the remote endpoint of the tunnel. However, unlike a point-to-point GRE tunnel, an mGRE tunnel can have multiple endpoints, which makes it difficult to determine which NBMA address to use for a given destination. This is where NHRP comes in.

NHRP is a protocol that is used to dynamically map the NBMA address of a remote endpoint to its corresponding tunnel IP address. When a packet is sent over an mGRE tunnel, it first needs to be sent to the NHRP server, which maintains a mapping of the NBMA address of each remote endpoint to its corresponding tunnel IP address. The NHRP server then forwards the packet to the appropriate endpoint using the mapped NBMA address.

In summary, NHRP is used to dynamically map the NBMA address of a remote endpoint to its corresponding tunnel IP address when mGRE is used.