Refer to the exhibit. A network technician is troubleshooting a connectivity problem on R2. The
technician enters the show cdp neighbors command at the R2 console. If the network is composed
only of Cisco devices, for which devices should entries be displayed?
A.
SW-B and R1
B.
R1
C.
R3, SW-B, R1, and SW-C
D.
SW-B, R1, and SW-C
E.
SW-A, R3, SW-B, R1, and SW-C
F.
Host A, SW-A, R3, SW-B, R1, and SW-C
Explanation:
The Cisco Discovery Protocol (CDP) discovers basic information about neighboring routers and
switches, without needing to know the passwords for the neighboring devices. CDP supports any
LAN, HDLC, Frame Relay, and ATM interface-in fact, it supports any interface that supports the
use of SNAP headers. The router or switch can discover Layer 2 and Layer 3 addressing details of
neighboring routers without even configuring that Layer 3 protocol-this is because CDP is not
dependent on any particular Layer 3 protocol. When Cisco first developed the proprietary CDP, it
was used mainly between routers. Today most Cisco products support CDP, including Cisco
switches and Cisco IP Phones. Devices that support CDP advertise their own information and
learn information about others by listening for their advertisements. On media that support
multicasts at the data link layer, CDP uses multicast; on other media, CDP sends a copy of the
CDP update to any known data-link addresses. So, any CDP-supporting device that shares a
physical medium with another CDP-supporting device can learn about the other device.
CDP discovers several useful details from the neighboring device:
Device identifier -Typically the host name
Address list -Network and data-link addresses
Port identifier -Text that identifies the port, which is another name for an interface
Capabilities list -Information on what type of device it is-for instance, a router or a switch
Platform -The model and OS level running in the device
CDP is enabled in the configuration by default. The no cdp run global command disables CDP for
the entire device, and the cdp run global command re-enables CDP. Likewise, the no cdp enable
interface subcommand disables CDP just on that interface, and the cdp enable command switches
back to the default state of CDP being enabled.