VLANs Flashcards
True or False:
Traffic within the same VLAN must be switched.
True
True or False:
Traffic outside or between VLAN’s must be routed.
True
How many bits defines a VLAN?
12 bit field defines a VLAN (2-4094)
Where are VLAN’s Stored
VLAN.DAT file
Normal VLAN Range?
1-1005 1=default 1002/1004=FDDI 1003/1005= Token Ring
What categories do L2 switchports fall into?
Access Ports, Trunk Ports, Dynamic switch ports (DTP).
When you issue a command show port 3/1 on an Ethernet port, you observe the ‘Giants’ column has a non-zero entry. What could cause of this?
A. IEEE 802.1Q
B. IEEE 802.10
C. Misconfigured NIC
D. User configuration
E. All of the above
Answer: A
Explanation
Generally, frames that are greater than 1522 bytes are categorized as giant frames (notice that a normal Ethernet frame has a size that ranges from 64 bytes to 1518 bytes). Giant frames often are the result of some protocol-tagging mechanisms, for example 802.1Q frames (1522 bytes), MPLS (1518 + 4 * n, where n is the number of stacked labels), ISL frames (1548 bytes).
There are nothing wrong with giant frames, just make sure you configure both end devices to support these frames.
Note: In fact, frames that are created by 802.1Q are often known as baby giants (frames that are slightly larger than 1518 bytes).
You want to configure a switched internetwork with multiple VLANs as shown above. Which of the following commands should you issue on SwitchA for the port connected to SwitchB?
switchport_mode_trunk.jpg
A. switchport mode trunk
B. switchport access vlan 5
C. switchport mode access vlan 5
D. switchport trunk native vlan 5
Answer: A
Explanation
To support interVLAN routing, the links between two switches must be configured as trunk link.
Refer to the exhibit. VLAN 1 and VLAN 2 are configured on the trunked links between Switch A and Switch B. Port Fa 0/2 on Switch B is currently in a blocking state for both VLANs. What should be done to load balance VLAN traffic between Switch A and Switch B?
trunk_blocking_state.jpg
A. Lower the port priority for VLAN 1 on port 0/1 for Switch A.
B. Lower the port priority for VLAN 1 on port 0/2 for Switch A.
C. Make the bridge ID of Switch B lower than the ID of Switch A.
D. Enable HSRP on the access ports.
Answer: B
Explanation
Please read the explanation of Question 1 in http://www.certprepare.com/vlan-vtp-stp-questions.
In general, lower the port priority for VLAN 1 will lower the Root Bridge ID for port Fa0/2 on Switch A -> traffic for VLAN 1 will flow via Fa0/2 link.
Refer to the exhibit and the show interfaces fastethernet0/1 switchport outputs. Users in VLAN 5 on switch SW_A complain that they do not have connectivity to the users in VLAN 5 on switch SW_B. What should be done to fix the problem?
show_interfaces_fastethernet_switchport_switch.jpg
A. Configure the same number of VLANs on both switches.
B. Create switch virtual interfaces (SVI) on both switches to route the traffic.
C. Define VLAN 5 in the allowed list for the trunk port on SW_A.
D. Disable pruning for all VLANs in both switches.
E. Define VLAN 5 in the allowed list for the trunk port on SW_B.
Answer: C
Explanation
SW_A is missing VLAN 5 in the “Trunking VLANs Enabled”, that means the trunk link currently does not accept traffic from VLAN 5 to be sent on the link.
Refer to the show interface Gi0/1 switchport command output shown in the exhibit. Which two statements are true about this interface? (Choose two)
show_interface_gigabitethernet_access.jpg
A. This interface is a member of a voice VLAN.
B. This interface is configured for access mode.
C. This interface is a dot1q trunk passing all configured VLANs.
D. This interface is a member of VLAN 7.
E. This interface is a member of VLAN 1.
Answer: B D
Refer to the following exhibits (exhibit 2 on answer side):
Exhibit #1
show_interfaces_fastethernet_switchport_dynamic_auto.jpg
Exhibit #2
show_interfaces_fastethernet_switchport_dynamic_desirable.jpg
Study the exhibits carefully. The switchport output in Exhibit #1 displays the default settings of interface FastEthernet 0/13 on switch Sw1. Figure 2 displays the desired interface settings. Which command sequence would configure interface FastEthernet 0/13 as displayed in Exhibit #2?
A.
Sw1(config-if)# switchport trunk encapsulation dot1q
Sw1 (config-if)# switchport mode dynamic auto
Sw1 (config-if)# switchport trunk native DATA
Sw1 (config-if)# switchport trunk allowed vlan add 1,10,20
B.
Sw1(config-if)# switchport trunk encapsulation dot1q
Sw1(config-if)# switchport mode dynamic desirable
Sw1(config-if)# switchport trunk native vlan DATA
Sw1(config-if)# switchport trunk allowed vlan 1,10,20
C.
Sw1 (config-if)# switchport trunk encapsulation dot1q
Sw1 (config-if)# switchport mode trunk
Sw1 (config-if)# switchport trunk native DATA
Sw1 (config-if)# switchport trunk allowed vlan 1,10,20
D.
Sw1(config-if)# switchport trunk encapsulation dot1q
Sw1(config-if)#switchport mode dynamic desirable
Sw1(config-if)#switchport trunk native vlan 10
E.
Sw1 (config-if)# switchport trunk encapsulation dot1q
Sw1 (config-if)# switchport mode dynamic desirable
Sw1 (config-if)# switchport trunk native vlan 10
Sw1 (config-if)# switchport trunk allowed vlan 1,10,20
Answer: E
Refer to the exhibit. Based upon the output of show vlan on switch CAT2, what can we conclude about interfaces Fa0/13 and Fa0/14?
show_vlan.jpg
A. That interfaces Fa0/13 and Fa0/14 are in VLAN 1
B. That interfaces Fa0/13 and Fa0/14 are down
C. That interfaces Fa0/13 and Fa0/14 are trunk interfaces
D. That interfaces Fa0/13 and Fa0/14 have a domain mismatch with another switch
E. That interfaces Fa0/13 and Fa0/14 have a duplex mismatch with another switch
Answer: C
Explanation
Trunk ports are part of multiple VLANs, not of just a single VLAN so they never show up in the show vlan command. You can check the trunk port with the show interfaces trunk or show interface {port} switchport command. You can find an example output of this command in Question 8.
Note: Trunk ports that are not connected appear by default in vlan 1 and also appear in the output of the show vlan command.
What two pieces of information will the show vlan id 5 command display? (Choose two)
A. Ports in VLAN 5
B. Utilization
C. VLAN information on port 0/5
D. Filters
E. MTU and type
Answer: A E
Explanation
The show vlan id vlan-id command display information about a particular VLAN. But notice that this command will also list trunk ports that allow this VLAN to run on. An example of the “show vlan id” command is shown below:
On a multilayer Catalyst switch, which interface command is used to convert a Layer 3 interface to a Layer 2 interface?
A. switchport access vlan vlan-id
B. switchport
C. switchport mode access
D. no switchport
Answer: B
In the three-layer hierarchical network design model; what’s associated with the access layer? (Choose two)
A. optimized transport structure
B. high port density
C. boundary definition
D. data encryption
E. local VLANs
F. route summaries
Answer: B E
Explanation
Main characteristics of three layers in the three-layer hierarchical network design model:
* Access layer:
+ Low cost per switch port
+ High port density
+ Scalable uplinks to higher layers
+ User access functions such as VLAN membership, traffic and protocol filtering, and quality of service (QoS)
+ Resiliency through multiple uplinks
* Distribution Layer:
+ Aggregation of multiple access-layer devices
+ High Layer 3 throughput for packet handling
+ Security and policy-based connectivity functions through access lists or packet filters
+ QoS features
+ Scalable and resilient high-speed links to the core and access layers
* Core layer:
+ Very high throughput at Layer 3
+ No costly or unnecessary packet manipulations (access lists, packet filtering)
+ Redundancy and resilience for high availability
+ Advanced QoS functions
Also, end-to-end VLANs and local VLANs belong to access layer.
Refer to the exhibit. The user who is connected to interface FastEthernet 0/1 is on VLAN 10 and cannot access network resources. On the basis of the information in the exhibit, which command sequence would correct the problem?
A. SW1(config)# vlan 10
SW1(config-vlan)# no shut
B. SW1(config)# interface fastethernet 0/1
SW1(config-if)# switchport mode access
SW1(config-if)# switchport access vlan 10
C. SW1(config)# interface fastethernet 0/1
SW1(config-if)# switchport mode access
D. SW1(config)# vlan 10
SW1(config-vlan)# state active
E. SW1(config)# interface fastethernet 0/1
SW1(config-if)# no shut
Answer: E
What are some virtues of implementing end-to-end VLANs? (Choose two)
A. End-to-end VLANs are easy to manage.
B. Users are grouped into VLANs independent of a physical location.
C. Each VLAN has a common set of security and resource requirements for all members.
D. Resources are restricted to a single location.
Answer: B C
Explanation
There are two kinds of VLANs:
* End-to-end VLANs: also called campuswide VLANs, span the entire switch fabric of a network. They are positioned to support maximum flexibility and mobility of end devices. Users can be assigned to VLANs regardless of their physical location. As a user moves around the campus, that user’s VLAN membership stays the same. End-to-end VLANs should group users according to common requirements. All users in a VLAN should have roughly the same traffic flow patterns
* Local VLANs: based on geographic locations by demarcation at a hierarchical boundary (core, distribution, access)
(Reference: CCNP SWITCH 642-813 Official Certification Guide)
Which two statements are true about a switched virtual interface (SVI)? (Choose two)
A. An SVI is created by entering the no switchport command in interface configuration mode.
B. An SVI is normally created for the default VLAN (VLAN1) to permit remote switch administration.
C. An SVI provides a default gateway for a VLAN.
D. Multiple SVIs can be associated with a VLAN.
E. SVI is another name for a routed port.
Answer: B C
Explanation
Catalyst L2 fixed configuration switches that run Cisco IOS Software have only one configurable IP management interface, which by default is interface VLAN 1. Pure layer 2 switches can have only one interface VLAN up at the time. This is called the management VLAN (in IOS) or the sc0 interface (in CatOS). The main purpose of this interface is management (telnet, SNMP, etc). If the switch is a Layer 3 switch, you can configure multiple VLANs and route between them. An L3 switch can handle multiple IPs, so there is no specific management VLAN on the switch.
(Reference: http://www.cisco.com/en/US/products/hw/switches/ps708/products_tech_note09186a008010e9ca.shtml)
You have just created a new VLAN on your network. What is one step that you should include in your VLAN based implementation and verification plan?
A. Verify that trunked links are configured to allow the VLAN traffic.
B. Verify that the switch is configured to allow for trunking on the switch ports.
C. Verify that each switch port has the correct IP address space assigned to it for the new VLAN.
D. Verify that different native VLANs exist between two switches for security purposes.
Answer: A
Explanation
A VLAN-based implementation and verification plan should include:
* Verification that trunked links are configured to allow the newly created VLANs.
* Verification that the SVI has already been created and that it shows up on all required switches using the show vlan command.
You have just created a new VLAN on your network for inter-VLAN routing. What is one step that you should include in your VLAN-based implementation and verification plan?
A. Verify that different native VLANs exist between two switches for security purposes.
B. Verify that the switch is configured to allow for trunking on the switch ports.
C. Verify that each switch port has the proper IP address space assigned to it for the new VLAN.
D. Verify that the VLAN virtual interface has been correctly created and enabled.
Answer: D
Explanation
Same as Question 5.
Which of the following technologies would an Internet Service Provider use to support overlapping customer VLAN ID’s over transparent LAN services?
A. 802.1q tunneling
B. ATM
C. SDH
D. IP Over Optical Networking
E. ISL
Answer: A
Explanation
Using the IEEE 802.1Q tunneling (QinQ) feature, service providers can use a single VLAN to support customers who have multiple VLANs. The trick here is instead of removing the VLAN tag received from customers, the ISP’s edge switch puts that traffic into the VLAN assigned to that port and adds another VLAN tag outside that tag. Let’s see an example:
802_1q_tunneling_QinQ.jpg
When Switch A (of the Service Provider) receives customer traffic from an 802.1Q trunk port, it does not strip the received 802.1Q tag from the frame header; instead, the tunnel port leaves the 802.1Q tag intact, adds a 1-byte Ethertype field (0×8100) and a 1-byte length field and puts the received customer traffic into the VLAN to which the tunnel port is assigned. This Ethertype 0×8100 traffic, with the received 802.1Q tag intact, is called tunnel traffic. Notice that “VLAN X” here can be one or multiple VLANs, all will be tagged with VLAN 4 (suppose VLAN 4 is assigned to Company A).
A benefit of 802.1qQ tunneling is multiple companies can use the overlapped VLANs. For example, Company A can use VLANs 1 to 100 while Company B can use VLANs 50 to 100 (overlapped from VLANs 50 to 100). The ISP’s switches can still classify them because they are attached to different outer VLAN tags. In the example above Company A is assigned to VLAN 4 so we can assign Company B to VLAN 5, Company C to VLAN 6 and so on.
The link between the 802.1Q trunk port on a customer device and the tunnel port is called an asymmetrical link because one end is configured as an 802.1Q trunk port and the other end is configured as a tunnel port.
Note: By default, the native VLAN traffic of a dot1q trunk is sent untagged, which cannot be double-tagged in the service provider network. Because of this situation, the native VLAN traffic might not be tunneled correctly. Be sure that the native VLAN traffic is always sent tagged in an asymmetrical link. To tag the native VLAN egress traffic and drop all untagged ingress traffic, enter the global vlan dot1q tag native command.
(Reference: http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/dot1qtnl.html)
Under what circumstances should an administrator prefer local VLANs over end-to-end VLANs?
A. Eighty percent of traffic on the network is destined for Internet sites.
B. There are common sets of traffic filtering requirements for workgroups located in multiple buildings.
C. Eighty percent of a workgroup’s traffic is to the workgroup’s own local server.
D. Users are grouped into VLANs independent of physical location.
Answer: A
Explanation
End-to-end VLAN follows the 80/20 rule in which 80 percent of user traffic stays within the local workgroup, whereas 20 percent is destined for a remote resource in the campus network (like Internet…).
In contrast to end-to-end-VLAN, local VLAN follows the 20/80 rule: only 20 percent of traffic is local, whereas 80 percent is destined to a remote re-source across the core layer -> A is correct.
(Reference: CCNP SWITCH 642-813 Official Certification Guide)
Which of the following statements is true about the 80/20 rule (Choose two)?
A. 20 percent of the traffic on a network segment should be local.
B. no more than 20 percent of the network traffic should be able to move across a backbone.
C. no more than 80 percent of the network traffic should be able to move across a backbone.
D. 80 percent of the traffic on a network segment should be local.
Answer: B D
Explanation
The 80/20 rule states that 80 percent of user traffic stays within the local workgroup, whereas 20 percent is destined for a remote resource in the campus network
Which two statements are true about best practices in VLAN design? (Choose two.)
A. Routing should occur at the access layer if voice VLANs are utilized. Otherwise, routing should occur at the distribution layer.
B. Routing may be performed at all layers but is most commonly done at the core and distribution layers.
C. Routing should not be performed between VLANs located on separate switches.
D. VLANs should be local to a switch.
E. VLANs should be localized to a single switch unless voice VLANs are being utilized.
Answer: B D
Explanation
First let’s review main characteristics of three layers in a campus network:
* Access layer:
+ Low cost per switch port
+ High port density
+ Scalable uplinks to higher layers
+ User access functions such as VLAN membership, traffic and protocol filtering, and quality of service (QoS)
+ Resiliency through multiple uplinks
* Distribution Layer:
+ Aggregation of multiple access-layer devices
+ High Layer 3 throughput for packet handling
+ Security and policy-based connectivity functions through access lists or packet filters
+ QoS features
+ Scalable and resilient high-speed links to the core and access layers
* Core layer:
+ Very high throughput at Layer 3
+ No costly or unnecessary packet manipulations (access lists, packet filtering)
+ Redundancy and resilience for high availability
+ Advanced QoS functions
We can see at Distribution and Core layers, Layer 3 throughput (routing) is very high -> B is correct.
Nowadays, end-to-end VLANs are not recommended in an enterprise network, unless there is a good reason. In an end-to-end VLAN, broadcast traffic is carried over from one end of the network to the other, creating the possibility for a broadcast storm or Layer 2 bridging
loop to spread across the whole extent of a VLAN. This can exhaust the bandwidth of distribution and core-layer links, as well as switch CPU resources. Now the storm or loop has disrupted users on the end-to-end VLAN, in addition to users on other VLANs that might
be crossing the core.
When such a problem occurs, troubleshooting becomes more difficult. In other words, the risks of end-to-end VLANs outweigh the convenience and benefits.
From that we can infer VLAN traffic should be local to the switch -> D is correct.
(Reference: CCNP SWITCH 642-813 Official Certification Guide)
You have configured a Cisco Catalyst switch to perform Layer 3 routing via an SVI and have assigned that interface to VLAN 20. To check the status of the SVI, you issue the show interfaces vlan 20 command at the CLI prompt. You see from the output display that the interface is in an “up/up” state. What must be true in an SVI configuration to bring the VLAN and line protocol up?
A. The port must be physically connected to another Layer 3 device.
B. At least one port in VLAN 20 must be active.
C. The Layer 3 routing protocol must be operational and receiving routing updates from neighboring peer devices.
D. Because this is a virtual interface, the operational status will always be in an “up/up” state.
Answer: B
Explanation
To be “up/up,” a router VLAN interface must fulfill the following general conditions:
* The VLAN exists and is “active” on the VLAN database of the switch.
* The VLAN interface exists on the router and is not administratively down.
* At least one Layer 2 (access port or trunk) port exists, has a link “up” on this VLAN and is in spanning-tree forwarding state on the VLAN.
(Reference: http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/12.2/37sg/configuration/guides/l3_int.html)
Let’s see an example of configuring Switch Virtual Interface (SVI) to perform interVLAN routing between PC0 & PC1:
SVI_simple_topology.jpg
Configuration
//Create two VLANs
L3Switch(config)#vlan 10
L3Switch(config-vlan)#vlan 20
L3Switch(config-vlan)#exit
L3Switch(config)#interface fa0/1
L3Switch(config-if)#switchport mode access
L3Switch(config-if)#switchport access vlan 10
L3Switch(config)#interface fa0/2
L3Switch(config-if)#switchport mode access
L3Switch(config-if)#switchport access vlan 20
L3Switch(config-if)#exit
//Enable IP routing on this Layer 3 Switch
L3Switch(config)#ip routing
//Create two SVIs for interVLAN routing:
L3Switch(config)#interface vlan 10
L3Switch(config-if)#ip address 10.0.0.1 255.255.255.0
L3Switch(config)#interface vlan 20
L3Switch(config-if)#ip address 20.0.0.1 255.255.255.0
On PC0, assign the IP address 10.0.0.2 255.255.255.0 and the default gateway: 10.0.0.1
On PC1, assign the IP address 20.0.0.2 255.255.255.0 and the default gateway: 20.0.0.1
Now we can ping from PC0 to PC1:
PC0>ping 20.0.0.2
Pinging 20.0.0.2 with 32 bytes of data:
Reply from 20.0.0.2: bytes=32 time=40ms TTL=127
Reply from 20.0.0.2: bytes=32 time=40ms TTL=127
Reply from 20.0.0.2: bytes=32 time=40ms TTL=127
Reply from 20.0.0.2: bytes=32 time=40ms TTL=127
You are assigning VLANs to the ports of switch R1. What VLAN number value is an assigned to the default VLAN?
A VLAN 1003
B. VLAN 1
C. VLAN ON
D. VLAN A
E. VLAN 0
Answer: B
What is a characteristic of a static VLAN membership assignment?
A. VMPS server lookup is required
B. Easy to configure
C. Ease of adds, moves, and changes
D. Based on MAC address of the connected device
Answer: B
Explanation
There are two types of VLAN membership assignment:
* Static VLAN: switch ports are assigned to specific VLANs manually
* Dynamic VLAN: switch automatically assigns the port to a VLAN using information from the user device like MAC address, IP address etc. When a device is connected to a switch port, the switch must, in effect, query a database to establish VLAN membership.
Static VLAN assignment provides a simple way to assign VLAN to a port while Dynamic VLANs allow a great deal of flexibility and mobility for end users but require more administrative overhead.
