Which two statements describe operations performed by the encapsulating tunnel endpoint in an IP- IP tunnel? (Choose two.)

When an IP packet enters an IP-IP tunnel, the encapsulating endpoint performs two key operations. First, it treats the original packet as if it were forwarding it, which includes decrementing the Time-to-Live (TTL) field in the original (inner) IP header by one. This is standard router behavior to prevent indefinite packet looping. Second, it creates a new, outer IP header. The source address of this new header is the encapsulating router's tunnel interface, and the destination address is the IP address of the remote tunnel endpoint (the decapsulator). The original IP packet then becomes the payload of this new IP packet.

B. The purpose of the tunnel is to transparently carry the original packet. Modifying the source and destination addresses in the inner header would break end-to-end connectivity.

D. A new outer header is created and added, not a new inner header. The original inner header is preserved and encapsulated within the new outer packet.

1. IETF RFC 2003, "IP Encapsulation within IP": This document defines the standard for IP-IP tunneling.

Section 4.1, "Encapsulator": "The encapsulator creates an outer IP header... The IP Destination Address in the outer IP header is the IP address of the decapsulator... The TTL in the inner IP header is decremented by one if the packet is being forwarded." This directly supports answers C and A.

2. Juniper Networks Documentation, "Junos OS Services Interfaces Library for Routing Devices": This guide details the configuration and operation of tunnel services on Junos devices.

Section: "IP-IP Tunneling Overview": The documentation explains that an IP-IP tunnel is configured with a tunnel source and tunnel destination. This configured destination address is used as the destination in the outer IP header, which supports answer C. The device's adherence to standard IP forwarding principles (as defined in RFCs) implies the TTL decrement described in answer A.