Disables or enables CDP on specific interfaces
What are the three
major steps in troubleshooting in the ICND1 Official Cert Guide?
·
Step 1.
Analyzing/predicting normal operation: Predict the details of what should
happen if the network is working correctly, based on documentation,
configuration, and show and debug command output. Step 2. Problem isolation:
Determine how far along the expected path the frame/packet goes before it
cannot be forwarded any farther, again based on documentation, configuration,
and show and debug command output.
Step 3. Root cause analysis: Identify the underlying causes of the problems
identified in the preceding step—specifically, the causes that have a specific
action with which the problem can be fixed.
Cisco Discovery
Protocol (CDP)
·
Used to confirm the
documentation, and learn about the network topology, to predict normal
operation of the network.
What are some details
provided via CDP of neighboring Cisco devices?
• Device identifier: Typically the host name •
Address list: Network and data link addresses
• Port identifier: The interface on the remote router or switch on the other
end of the link that sent the CDP advertisement
• Capabilities list: Information on what type of device it is (for example, a
router or a switch)
• Platform: The model and OS level running on the device
Show cdp neighbors
[type number] command
·
Lists one summary line
of information about each neighbor, or just the neighbor found in a specific
interface if an interface was listed.
Show cdp neighbors
detail command
·
List one large set
(approximately 15 lines) of information, one set for every neighbor
Show cdp entry name
command
·
List the same
information as the show cdp neighbors detail command, but only for the named
neighbor (case sensitive)
no cdp enable/cdp
enable commands
·
Disables or enables
CDP on specific interfaces
no cdp run/cdp run
command
·
Disables or enables
CDP for an entire switch
show cdp command
·
States whether CDP is
enabled globally, and lists the default update and holdtime timers.
show cdp interface
[type number] command
·
States whetere CDP is
enabled on each interface, or a single interface if the interface is listed,
and states update and holdtime timers on those interfaces.
show cdp traffic
command
·
Lists global
statistics for the number of CDP advertisements sent and received.
What is the two-code
status presented when entering the commands "show interfaces" or
"show interfaces description"
·
The line status and
protocol status. They generally refer to whether Layer 1 is working (line
status) and whether Layer 2 is working (protocol status), respectively. LAN
switch interfaces typically show an interface with both codes with the same
value, either "up" or "down."
With the "show
interfaces status" command what are some of the single interface status
codes presented?
·
disabled,
nonconnected, err-disabled, connected
If an interface's
duplex settings have it as "full" instead of "a-full" what
is the difference?
·
Full means the ports
is manually running at full duplex while a-full means the port is running at
full duplex via autonegotiation
Runts
·
Frames that did not
meet the minimum frame size requirement (64 bytes, including the 18byte
destination MAC, source MAC, Type, and FCS). Can be caused by collisions.
Giants
·
Frames that exceed the
maximum frame size requirement (1518 bytes, including the 18byte destination
MAC, source MAC, Type, and FCS).
Input Errors
·
A total of many
counters, including runts, giants, no buffer, CRC, frame, overrun, and ignored
counts.
CRC
·
Received frames that
did not pass the FCS math; can be caused by collisions. Frame: Received frames
that have an illegal format, for example, ending with a partial byte; can be
caused by collisions.
Packets Output
·
Total number of
packets (frames) forwarded out the interface
Output Errors
·
Total number of
packets (frames) that the switch port tried to transmit, but for which some
problem occurred.
Collisions
·
Counter of all
collisions that occur when the interface is transmitting a frame.
Late Collisions
·
The subset of all
collisions that happen after the 64th byte of the frame has been transmitted.
(In a properly working Ethernet LAN, collisions should occur within the first
64
bytes; late collisions today often point to a duplex mismatch.)
Show mac address-table
exec command
·
Displays the contents
of a switch's MAC address table
Show mac address-table
dynamic exec command
·
Displays a swith's mac
address table, but only learned mac addresses instead of learned and static
show vlan brief and
show vlan commands
·
Lists each VLAN and
all interfaces assigned to that VLAN (but does not include operational trunks)
show vlan id num
command
·
Lists both access and
trunk ports in the VLAN
show interfaces type
number switchport command
·
Identifies the
interface's access VLAN and voice VLAN, plus the configures and operational
mode (access or trunk)
show vlan command
·
List all VLANs known
to the switch
show vtp status
command
·
Displays the current
vtp mode of a switch
Show interfaces trunk
·
Shows a trunk port's
operational state
Imagine that a switch
connects through an Ethernet cable to a router, and the router's host name is
Hannah. Which of the following commands could tell you information about the
IOS version on Hannah without establishing a Telnet connection to Hannah?
(Choose two answers.)
a. show neighbors Hannah
b. show cdp
c. show cdp neighbors
d. show cdp neighbors Hannah
e. show cdp entry Hannah
f. show cdp neighbors detail
·
E and F. CDP discovers
information about neighbors. show cdp gives you several options that display
more or less information, depending on the parameters used.
A switch is cabled to
a router whose host name is Hannah. Which of the following CDP commands could
identify Hannah's model of hardware? (Choose two answers.)
a. show neighbors
b. show neighbors Hannah
c. show cdp
d. show cdp interface
e. show cdp neighbors
f. show cdp entry Hannah
·
E and F. The show cdp
neighbors command lists one line of output per neighbor. However, it does list
the platform information of the neighbor, which typically includes the hardware
model number. The show cdp entry Hannah command lists a group of messages about
the neighboring router, including more detail about the hardware model and the
IOS version.
The output of the show
interfaces status command on a 2960 switch shows interface Fa0/1 in a
"disabled" state. Which of the following is true about interface
Fa0/1? (Choose three answers.)
a. The interface is configured with the shutdown command.
b. The show interfaces fa0/1 command will list the interface with two status
codes of administratively down and line protocol down.
c. The show interfaces fa0/1 command will list the interface with two status
codes of up and down.
d. The interface cannot currently be used to forward frames.
e. The interface can currently be used to forward frames.
·
A, B, and D. The
disabled state in the show interfaces status command is the same as an
"administratively down and down" state shown in the show interfaces
command. The interface must be in a connected state (per the show interfaces
status command) before the switch can send frames out the interface.
Switch SW1 uses its
Gigabit 0/1 interface to connect to switch SW2's Gigabit 0/2 interface. SW2's
Gi0/2 interface is configured with the speed 1000 and duplex full commands. SW1
uses all defaults for interface configuration commands on its Gi0/1 interface.
Which of the following are true about the link after it comes up? (Choose two
answers.)
a. The link works at 1000 Mbps (1 Gbps).
b. SW1 attempts to run at 10 Mbps because SW2 has effectively disabled IEEE
standard autonegotiation.
c. The link runs at 1 Gbps, but SW1 uses half-duplex and SW2 uses full-duplex.
d. Both switches use full-duplex.
·
A and D. SW2 has
effectively disabled IEEE standard autonegotiation by configuring both speed
and duplex. However, Cisco switches can detect the speed used by the other
device, even with autonegotiation turned off. Also, at 1 Gbps, the IEEE
autonegotiation standard says to use full-duplex if the duplex setting cannot
be negotiated, so both ends use 1 Gbps, full-duplex.
The following line of
output was taken from a show interfaces fa0/1 command: Full-duplex, 100Mbps,
media type is 10/100BaseTX Which of the following are true about the interface?
(Choose two answers.)
a. The speed was definitely configured with the speed 100 interface subcommand.
b. The speed might have been configured with the speed 100 interface
subcommand.
c. The duplex was definitely configured with the duplex full interface
subcommand.
d. The duplex might have been configured with the duplex full interface
subcommand.
·
B and D. The show
interfaces command lists the actual speed and duplex setting, but it does not
imply anything about how the settings were configured or negotiated. The show
interfaces status command lists a prefix of a- in front of the speed and duplex
setting to imply that the setting was autonegotiated, leaving off this prefix
if the setting was configured.
Which of the following
commands list the MAC address table entries for MAC addresses configured by
port security? (Choose two answers.)
a. show mac address-table dynamic
b. show mac address-table
c. show mac address-table static
d. show mac address-table port-security
·
B and C. IOS adds MAC
addresses configured by the port security feature as static MAC addresses, so
they do not show up in the output of the show mac address-table dynamic
command. show mac address-table port-security is not a valid command.
Layer 2 switches SW1
and SW2 connect through a link, with port G0/1 on SW1 and port G0/2 on SW2. The
network engineer wants to use 802.1Q trunking on this link. The show interfaces
g0/1 switchport command on SW1 shows the output listed here:
SW1# show interfaces gigabit0/1 switchport
Name: Gi0/1
Switchport: Enabled
Administrative Mode: trunk
Operational Mode: trunk
Which of the following must be true on switch SW2's G0/2 port?
a. The operational state per the show interfaces switchport command must be
"trunk."
b. The administrative state per the show interfaces switchport command must be
"trunk."
c. SW2 must use the switchport mode trunk configuration command on G0/2, or the
link will not use trunking.
d. SW2 can use the switchport mode dynamic auto configuration command as one
option to make the link use trunking.
·
D. The show interface
switchport command lists a switch's configured value of the switchport mode
command as the administrative mode, telling us that SW1 uses the switchport
mode trunk configuration command. The operation state shows the current working
state (trunk). Of the four answers, one incorrect answer claims that SW2's
operational state must also be "trunk"; however, one switch can use
trunking, while the other does not. Another answer claims that the
administrative mode must be "trunk," which basically means that the
command switchport mode trunk must be used. However, SW2 has a few other
configuration options that would work, like the switchport mode dynamic
desirable and switchport mode dynamic auto commands. The correct answer refers
to one of these commands that would work correctly.
USA 
India