Layer 3 Switching
V-LAN Interview Questions
OSPF Questions and Answers in CCNP
Networking Basics
Routing Information Protocol

Layer 3 Switching

1. What might you need to implement interVLAN routing?

** One or more Layer 3 interfaces

One or more SVIs

Static routes

A dynamic routing protocol

2. Can interVLAN routing be performed over a single trunk link?

** Yes. Packets can be forwarded between the VLANs carried over the trunk.

3. To configure an SVI, what commands are needed?

** First, make sure the VLAN is defined on the switch.

  • interface vlan vlan-id
  • ip address ip-address mask
  • no shutdown

4. What command can verify the VLAN assignments on a Layer 2 port?

** show interface type mod/num switchport


show interface status

5. A switch has the following interface configurations in its running configuration:

interface fastethernet 0/1
switchport access vlan 5
interface vlan 5
ip address
no shutdown
What is necessary for packets to get from the FastEthernet interface to the

Answer: Nothing. Both are assigned to VLAN 5, so normal Layer 2 transparent
bridging will take care of all forwarding between the two.

6. What is the source of FIB information?

** The routing table, as computed by the Layer 3 engine portion of a switch.

7. How often is the FIB updated?

** As needed. It is downloaded or updated dynamically by the Layer 3 engine
whenever the routing topology changes or an ARP entry changes.

 8. What is meant by the term “CEF punt”?

** A packet can’t be forwarded or switched by CEF directly because it needs
further processing. The packet is “punted” to the Layer 3 engine, effectively

bypassing CEF for a more involved resolution.

9. What happens to the FIB when distributed CEF (dCEF) is used?

** It is simply replicated to each of the independent CEF engines. The FIB itself
remains intact so that each engine receives a duplicate copy.

10. What happens during a “CEF glean” process?

** The MAC address (ARP reply) for a next-hop FIB entry is not yet known. The
Layer 3 engine must generate an ARP request and wait for a reply before CEF
forwarding can continue to that destination.

11. What does a multilayer switch do to the IP TTL value just before a
packet is forwarded?

** The TTL is decremented by one, as if a router had forwarded the packet.

12. What is fallback bridging?

** On switch platforms that cannot multilayer-switch (route) all routable protocols,
those protocols can be bridged transparently between VLANs instead.

13. Is it possible for an SVI to go down? If so, for what reasons?

** Yes. The SVI can be shut down administratively with the shutdown command,
as with any other interface. Also, if the VLAN associated with the SVI is not
defined or active, the SVI will appear to be down


V-LAN Interview Questions

1. What is a VLAN? When is it used?

Answer: A VLAN is a group of devices on the same broadcast domain, such aslogical subnet or segment. VLANs can span switch ports, switches within a
switch block, or closets and buildings. VLANs group users and devices into
common workgroups across geographical areas. VLANs help provide
segmentation, security, and problem isolation.

2. When a VLAN is configured on a Catalyst switch port, in how much of
the campus network will the VLAN number be unique and significant?

Answer: The VLAN number will be significant in the Escort Ajaccio local switch. If trunking is
enabled, the VLAN number will be significant across the entire trunking domainIn other words, the VLAN will be transported to every switch that has a trunk linsupporting that VLAN.

3. Name two types of VLANs in terms of spanning areas of the campus

Answer: Local VLAN
End-to-end VLAN

4. What switch commands configure Fast Ethernet port 4/11 for VLAN 2?

Answer: interface fastethernet 4/11
switchport mode access
switchport access vlan 2

5. Generally, what must be Escort Le Havre configuredfor a port-based VLAN?

Answer: The switch port

6. What is the default VLAN on all port

Answer: VLAN 1

7. What is a trunk link?

Answer: A trunk link is a cfrom multiple VLANs. Eacacross the trunk link.

8. What methods of EtheCatalyst switch trunk?

Answer: 802.1Q

9. What is the difference between the two trunking methods? How many
bytes are added to trunked frames for VLAN identification in each method?

Answer: ISL uses encapsulation and adds a 26-byte header and a 4-byte trailer.
802.1Q adds a 4-byte tag field within existing frames, without encapsulation.

10. What is the purpose of the Dynamic Trunking Protocol (DTP)?

Answer: DTP allows negotiation of a common trunking method between
endpoints of a trunk link.


11. What commands are needed to configure a Catalyst switch trunk port
Gigabit 3/1 to transport only VLANs 100, 200 through 205, and 300 using
IEEE 802.1Q? (Assume that trunking is enabled and active on the port
already. Also assume that the interface gigabit 3/1 command already has
been entered.

Answer: switchport trunk allowed vlan 100, 200-205, 300

12. Two neighboring switch trunk ports are set to the auto mode with ISL
trunking encapsulation mode. What will the resulting trunk mode become?

Answer: Trunking will not be established. Both switches are in the passive auto
state and are waiting to be asked to start the trunking mode. The link will remain
an access link on both switches.

13. Complete the following command to configure the switch port to use DTP to actively ask the other end to become a trunk:
switchport mode _________________

Answer: switchport mode dynamic desirable

14. Which command can set the native VLAN of a trunk port to VLAN 100
after the interface has been selected?

Answer: switchport trunk native vlan 100

15. What command can configure a trunk port to stop sending and
receiving DTP packets completely?

Answer: switchport nonegotiate

16. What command can be used on a Catalyst switch to verify exactly what
VLANs will be transported over trunk link gigabitethernet 4/4?

Answer: show interface gigabitethernet 4/4 switchport
show interface gigabitethernet 4/4 switchport trunk
17. Suppose that a switch port is configured with the following commands.
A PC with a nontrunking NIC card then is connected to that port. What, if
any, traffic will the PC successfully send and receive?

  1. interface fastethernet 0/12
  2. switchport trunk encapsulation dot1q
  3. switchport trunk native vlan 10
  4. switchport trunk allowed vlan 1-1005
  5. switchport mode trunk

Answer: The PC expects only a single network connection, using a single VLAN.
In other words, the PC can’t participate in any form of trunking. Only untagged or
unencapsulated frames will be understood. Recall that an 802.1Q trunk’s native
VLAN is the only VLAN that has untagged frames. Therefore, the PC will be
capable of exchanging frames only on VLAN 10, the native VLAN.


OSPF Questions and Answers in CCNP

1: Which command in OSPF shows the network LSA information?

** The command show ip ospf [process-id area-id] database network displays the
network link-state information.

2: What command would you use to create a totally stubby area?

** The command area area-id stub no-summary will create a totally stubby area.
This is a subcommand to the router ospf process-id command. It is necessary
only on the ABR, but all the other routers in the area must be configured as stub

 3: What is a virtual link, and what command would you use to create it?

** A virtual link is a link that creates a tunnel through an area to the backbone

(Area 0). This allows an area that cannot connect directly to the backbone to do
so virtually. The command to create the link is area area-id virtual-link router-id.
Note that the area-id that is supplied is that of the transit area, and the router-id is
that of the router at the other end of the link. The command needs to be
configured at both ends of the tunnel.
CCNP Question Answers

4: Where would you issue the command to summarize IP subnets? State the
command that is used.

** Summarization is done at area boundaries. The command to start
summarization is the area range command, with the syntax area area-id range
address mask. To summarize external routes, use the summary-address
command on the ASBRs.

 5: How would you summarize external routes before injecting them into the OSPF domain?

** The command summary-address address mask is the command that you would use.

6: When is a virtual link used?

** A virtual link is used when an area is not directly attached to the backbone area (Area 0). This may be due to poor design and a lack of understanding about the operation of OSPF, or it may be due to a link failure. The most common cause of an area separating from the backbone is link failure, which can also cause the backbone to be segmented. The virtual link is used in these instances
to join the two backbone areas together. Segmented backbone areas might also be the result of two companies merging.

 7: Give the command for defining the cost of a default route propagated into an area.

** The command to define the cost of a default route propagated into another
area is area area-id default-cost cost.

 8: Give an example of when it would be appropriate to define a default cost.

** It is appropriate to define a default cost for the default route when a stub area
has more than one ABR. This command allows the ABR or exit point for the areato be determined by the network administrator. If this link or the ABR fails, the
other ABR will become the exit point for the area.

9: On which router is the area default cost defined?

** The default cost for the default route is defined on the ABR. The ABR will then

automatically generate and advertise the route cost along with the default route.

10: Give the command to configure a stub area and state on which router it is

** The command syntax to configure a stub area is area area-id stub. This
command is configured on the ABR connecting to the area and on all the routers
within the area. Once the configuration is completed, the Hellos are generated
with the E bit set to 0. All routers in the area will only form adjacencies with other
routers that have the E bit set.

11: What is the purpose of the area range command, and why is it configured on the ABR?

** The area range command is configured on an ABR because it dictates the
networks that will be advertised out of the area. It is used to consolidate and
summarize the routes at an area boundary.

12: Give the commands to configure a router to place subnets  through to in Area 1 and to put all other interfaces into Area 0.

** The commands are as follows:

network area 1

network area 0
13: Give the syntax to summarize the subnets to into another autonomous system.

** The syntax is as follows:
14: Explain briefly the difference between the area range command and the summary-address command.

** The area range command is used to summarize networks between areas and
is configured on the ABR. The summary-address command is used to
summarize networks between autonomous systems and is configured on the


15: Explain the following syntax and what it will achieve: area 1 stub nosummary.


The command area 1 stub no-summary creates a totally stubby area.
The number after the word area indicates the area that is being defined as a totally stubby area.

This is necessary because the router might be an ABR with connections to many areas.

Once this command is issued, it prevents summarized and external routes from being propagated by the ABR into the area.

To reach the networks and hosts outside the area, routers must use the default route advertised by the ABR into the area.

 16: Why would you configure the routing process to log adjacency changes as opposed to turning on debug for the same trigger?

** The reason to configure the router process to log adjacency

changes to syslog as opposed to running debug is an issue of resources.

It takes fewer router and administrator resources to report on a change of state as it happens than to have the debugger running constantly. The debug process has the highest priority and thus everything waits for it.

17: Give some of the common reasons that neighbors fail to form an adjacency.

** Many OSPF problems stem from adjacency problems that propagate
throughout the network. Many problems are often traced back to neighbor

If a router configured for OSPF routing is not seeing an OSPF neighbor on an
attached network, do the following:


– Make sure that both routers are configured with the same IP mask, MTU,
Interface Hello timer, OSPF Hello interval, and OSPF dead interval.

– Make sure that both neighbors are part of the same area and area type.

– Use the debug and show commands to trace the problem.

18: When configuring a virtual link, which routers are configured?


** The configuration is between the ABRs, where one of the ABRs resides in
Area 0 and the other in the area that is disconnected from the backbone. Both of
the ABRs are also members of the transit area. Having created the virtual link,
both ABRs are now members of Area 0, the disconnected area, and the transit

19: What does the command area 1 default-cost 15 achieve?

** The command area 1 default-cost 15 will assign a cost of 15 to the default
route that is to be propagated into the stub area. This command is configured on
the ABR attached to the stub area.

20: Explain what is placed in the parameters area-id and router-id for the
command area area-id virtual-link router-id.

** The parameter area-id is the area ID of the transit area. So if the ABR in Area
0 is creating a virtual link with the ABR in Area 3 through Area 2, the area ID
stated in the command is Area 2. The router ID is the router ID of the router with
whom the link is to be formed and a neighbor relationship and adjacency


Networking Basics

1: What is the definition of a network?

** A network is a system of lines or channels that cross or interconnect, or a
group or system of electrical components and connecting circuitry designed to
function in a specific manner.

Networking Interview Questions

2: What are network models?

** Network models provide the guiding principles behind the development of
network standards.

3: What is a network standard, and why are there network standards?

** Network standards define the rules of network communication and are like
laws that must be followed for different equipment vendors to work together.

4: What is a proprietary feature?

** If a vendor implements a feature that does not adhere to any network
standards, it is called a proprietary feature.

5: What are the three data transmission modes, and how do they operate?

** Simplex mode, half-duplex mode, and full-duplex mode. Simplex mode is oneway communication only.
Half-duplex mode is two-way communication, but not at the same time. Full-duplex mode is simultaneous two-way communication.

6: List the major characteristics of a LAN.

** The primary characteristic of a LAN is its geographic coverage. LANs are

found in a small geographic area where there is a short distance between
connected computers, as in small offices or on each floor of a larger office
building. LANs enable the sharing of office resources, such as file servers for file
sharing among users or print servers for shared printers.

7: List the major characteristics of a MAN.

** MANs are found in a metropolitan, or citywide, geographic area,
interconnecting two or more office buildings in a broader geographic region than
a LAN would support, but not so broad that a WAN would be required.

8: List the major characteristics of a WAN.

** WANS are found in broad geographic areas, often spanning states and
countries, and are used to connect LANs and WANs together.

9: What are the three parts of a frame? What is a function of each part?

** Header, data (or payload), trailer. The header is the beginning of the frame,
significant in that the frame’s source and destination are found in the frame
header. The payload is the data part of the frame, the user’s information. The
trailer identifies the end of the frame.

10: What function in a network does cabling provide?

** Cabling provides the physical interconnection between network devices and nodes.

11: List some examples of user data.

** Examples of user data include e-mail, web-browsing traffic, word-processed
documents, spreadsheets, database updates.

12: What is the best definition of network topology?

** Network topology refers to the physical or logical geometric arrangement of
interconnected network devices.

13: What is the best definition of network protocol?

** A network protocol is the communication rules and formats followed by all
interconnected devices on a network requiring communication with one another.

14: What is the definition of network media?

** Network media refers to the physical component of a network. Communication
signals traverse network media from source to destination. Some examples of
network media are copper and fiber-optic cabling.

15: What is a network origination point?

** A network connection has two ends: the origination and termination points.
The origination point is the source of the data—the location from which the data
is being sent.

 16: What is a network termination point?

** A network connection has two ends: the origination and termination points.
The termination point is the destination of the data—the location to which the
data is being sent.



Routing Information Protocol

1:What port does RIP use?

* RIP uses UDP port 520.

2:What metric does RIP use? How is the metric used to indicate an
unreachable network?

* RIP uses a hop count metric. An unreachable network is indicated by setting
the hop count to 16, which RIP interprets as an infinite distance.

Routing Information Protocol

3:What is the update period for RIP?

* RIP sends periodic updates every 30 seconds minus a small random variable to
prevent the updates of neighboring routers from becoming synchronized.

4:How many updates must be missed before a route entry will be marked
as unreachable?

* A route entry is marked as unreachable if six updates are missed.

5:What is the purpose of the garbage collection timer?

* The garbage collection timer, or flush timer, is set when a route is declared
unreachable. When the timer expires, the route is flushed from the route table.
This process allows an unreachable route to remain in the routing table long
enough for neighbors to be notified of its status


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