A. A remote physical layer problem exists.
B. The host NIC is not functioning.
C. TCP/IP has not been correctly installed on the host.
D. A local physical layer problem exists.

A.switch to switch
B.switch to hub
C.switch to router
D.hub to hub
E.router to PC

A.The transport layer divides a data stream into segments and may add reliability and flow control information.
B.The data link layer adds physical source and destination addresses and an FCS to the segment.
C.Packets are created when the network layer encapsulates a frame with source and destination host addresses and protocol-related control information.
D.Packets are created when the network layer adds Layer 3 addresses and control information to a segment.
E.The presentation layer translates bits into voltages for transmission across the physical link.

A.802.1Q native VLAN frames are untagged by default.
B.802.1Q trunking ports can also be secure ports.
C.802.1Q trunks can use 10 Mb/s Ethernet interfaces.
D.802.1Q trunks require full-duplex, point-to-point connectivity.
E.802.1Q trunks should have native VLANs that are the same at both ends.

A.it is a layer 2 messaging protocol which maintains vlan configurations across network.
B.it includes an 8-bit field which specifies the priority of a frame.
C.it is used exclusively for tagging vlan frames and dose not address network reconvergence following switched network topology changes.
D.it modifies the 802.3 frame header，and thus requires that the FCS be recomputed.
E.it is a trunking protocol capable of carring untagged frames.