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Which two events occur when a packet is decapsulated in a GRE tunnel? (Choose two.)
Correct Answer: A,B
Explanation/Reference: Explanation: After the GRE encapsulated packet reaches the remote tunnel endpoint router, the GRE packet is decapsulated. The destination address lookup of the outer IP header (this is the same as the tunnel destination address) will find a local address (receive) entry on the ingress line card. The first step in GRE decapsulation is to qualify the tunnel endpoint, before admitting the GRE packet into the router, based on the combination of tunnel source (the same as source IP address of outer IP header) and tunnel destination (the same as destination IP address of outer IP header). If the received packet fails tunnel admittance qualification check, the packet is dropped by the decapsulation router. On successful tunnel admittance check, the decapsulation strips the outer IP and GRE header off the packet, then starts processing the inner payload packet as a regular packet. When a tunnel endpoint decapsulates a GRE packet, which has an IPv4/IPv6 packet as the payload, the destination address in the IPv4/IPv6 payload packet header is used to forward the packet, and the TTL of the payload packet is decremented. Reference: http://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/asr9k_r5-3/addr- serv/ configuration/guide/b-ipaddr-cg53asr9k/b-ipaddr-cg53asr9k_chapter_01001.html