Which statement is true about GRE tunnels?
A.
GRE tunnels can be used for only IP packets.
B.
GRE tunnels ensure that a packet does not live forever.
C.
Packets are encapsulated unchanged before entering the tunnel.
D.
GRE tunnels support point-to-multipoint.
B is correct – passed today with Tunnels section on 100%.
It is because GRE is changing original packet by lovering TTL, and by this it is ensuring, that packet will not live forever.
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Correct Mic
To encapsulate a GRE packet in an IP packet, a GRE header and an outer IP header are added. The GRE header and
outer IP header add an additional 24 bytes of overhead to the packet. The outer header includes the source IP
address, the entry point of the tunnel, and the destination IP address—the exit point of the tunnel. The inner packet
(also known as the payload packet) is not modified, except the time-to-live (TTL) field, which is decremented. The TTL
field must be decremented to ensure that the packet does not live forever. GRE packets that are encapsulated in IP
packets use IP protocol type 47.
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