Which Cisco IOS command is used to view the information about the interfaces on which Cisco Discovery
Protocol (CDP) is enabled?

A.
show cdp interface

B.
show interfaces

C.
show cdp

D.
show cdp interfaces

Explanation:
The show cdp interface command is used to view the information about the interfaces on which Cisco
Discovery Protocol (CDP) is enabled.
The syntax of the command is as follows:
Router# show cdp interface [type number]
The parameters of the command are as follows:
type: specifies the type of interface for which information is required
number: specifies the number of interfaces for which information is required
The output of the show cdp interface command is as follows:
Router#show cdp interface
Serial0 is up, line protocol is up, encapsulation is SMDS
Sending CDP packets every 100 seconds
Holdtime is 300 seconds
Serial1 is up, line protocol is up, encapsulation is SMDS
Sending CDP packets every 60 seconds
Holdtime is 180 seconds
Ethernet0 is up, line protocol is up, encapsulation is ARPA
Sending CDP packets every 120 seconds
Holdtime is 360 seconds
The show interfaces command is incorrect because this command is used to view configured interfaces on the
router. The output of this command can be very useful, especially when troubleshooting a connection with no
connectivity. Consider the output of the command on the following two routers that are connected with a serial
interface:
NewYork#show interfaces s0
Serial0 is up, line protocol is up
Hardware is HD64570
Internet Address is 192.168.10.1/24
MTU 1500 bytes,BW 1544 Kbit
Reliability 255/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
LosAngeles#show interfaces s1
Serial0 is up, line protocol is up
Hardware is HD64570
Internet Address is 192.168.11.2/24
MTU 1500 bytes,BW 56000 Kbit
Reliability 255/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
Notice that the following settings are correct:
The encapsulation matches (HDLC)
The physical connection is good (indicated by Serial0 is up)
Notice, however, that the IP addresses 192.168.10.1 and 192.168.11.2 are NOT in the same subnet when
using a 24-bit mask. With a 24-bit mask, the two addresses should agree through the first three octets, and
these do not. Problems such as this can be located through inspection of the output produced by the show
interfaces command.The show cdp command is incorrect because this command is used to view the global CDP information.
The show cdp interfaces command is incorrect because this command does not exist in the Cisco command
reference. There is a show cdp interface command, which displays CDP activity on a per-interface basis.
Objective:
LAN Switching Fundamentals
Sub-Objective:
Configure and verify Layer 2 protocols

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