CCNP 642-811 BCMSN Exam Certification Guide - Cisco press

536Appendix A: Answers to Chapter “Do I Know This Already?” Quizzes and Q&A Sections

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

Trunking will not be established at all. 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 this command to configure the switch port to use DTP to actively ask the other end to become a trunk:

switchport mode

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?

switchport trunk native vlan 100

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

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?

show interface gigabitethernet 4/4 switchport

-OR-

show interface gigabitethernet 4/4 trunk

17.Suppose a switch port is configured with the following commands. A PC with a nontrunking NIC card is then connected to that port. What, if any, traffic will the PC successfully send and receive?

interface fastethernet 0/12 switchport trunk encapsulation dot1q switchport trunk native vlan 10 switchport trunk allowed vlan 1-1005 switchport mode trunk

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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 able to exchange frames only on VLAN 10, the native VLAN.

18.What type of switch port must a customer present to a service provider if an IEEE 802.1Q tunnel is desired?

802.1Q trunk

19.What type of switch port must a service provider present to a customer if an IEEE 802.1Q tunnel is desired?

802.1Q tunnel

20.What command is needed to form a Layer 2 protocol tunnel for CDP traffic? l2protocol-tunnel cdp

Chapter 7

“Do I Know This Already?”

1.c

2.a

3.c

4.b

5.b

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12.b

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Q&A

1.True or false: You can use VTP domains to separate broadcast domains.

Answer: False. Broadcast domains can be separated only with VLANs because a VLAN defines a broadcast domain’s boundaries. A VTP domain is a different concept; it defines the management domain where a set of switches can exchange information about VLAN configuration.

2.What VTP modes can a Catalyst switch be configured for? Can VLANs be created in each of the modes?

Server, client, and transparent modes. VLANs can be created in server mode. VLANs cannot be created in client mode. In transparent mode, VLANs can be created, but only on the local switch; they are not advertised to other switches.

3.How many VTP management domains can a Catalyst switch participate in? How many VTP servers can a management domain have?

A switch can be a member of only one VTP management domain. A domain must have at least one server for VLAN changes to be propagated throughout the domain. There can be more than one server for redundancy.

4.What conditions must exist for two Catalyst switches to be in the same VTP management domain?

Both switches must have the same VTP domain name defined and enabled; both switches must be adjacent on a trunk link; and trunking must be enabled and active between them.

Two switches can also operate in the same VTP domain if one of them is new and has the default NULL domain name. That switch will listen and pick up the first VTP domain name it hears in VTP advertisements.

5.On a VTP server switch, identify what you can do to reset the VTP configuration revision number to 0.

Set the VTP domain name to a bogus value and change it back.

Configure the switch for VTP transparent mode and then configure the switch back to server mode.

6.How can you clear the configuration revision number on a VTP client?

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You can’t. The VTP client bases all VLAN and VTP information on advertisements from a VTP server. Therefore, the configuration revision number on the client comes directly from the same number on the server.

7.Complete this command to make all VLANs other than 30 and 100 eligible for pruning on the trunk interface:

switchport trunk pruning vlan

switchport trunk pruning vlan except 30,100

8.Which VLAN numbers are never eligible for VTP pruning? Why?

VLAN numbers 1 and 1001 to 1005. VLAN 1 is reserved as a VLAN for control protocol traffic, while VLANs 1002 to 1005 are reserved as the default FDDI and Token Ring function VLANs.

9.What does the acronym VTP stand for? VLAN Trunking Protocol

10.What VTP domain name is defined on a new switch with no configuration?

A NULL or empty string. The switch defaults to server mode and will learn a VTP domain name from the first VTP server heard on a trunk link. Otherwise, you must manually configure the domain name.

11.In a network of switches, VTP domain Engineering has been configured with VLANs 1, 10 through 30, and 100. The VTP configuration revision number is currently at 23. Suppose a new switch is connected to the network, and it has the following configuration: VTP domain Engineering, VTP server mode, only VLANs 1 and 2 are defined, and the configuration revision number is 30.

What will happen when the switch is connected to the network?

Because the new switch has a higher configuration revision number, the other switches in the VTP domain Engineering will learn all of its VLAN and VTP configuration information. The new switch has two VLANs configured on itself—VLAN 1 and 2. The other switches will assume they should delete all VLANs except for VLAN 1, and VLAN 2 will be created. Obviously, this will cause a major outage on the network because active VLANs 10 through 30 and 100 will be deleted and will go inactive. A network administrator will have to manually restore the configurations of those VLANs.

540Appendix A: Answers to Chapter “Do I Know This Already?” Quizzes and Q&A Sections

12.A VTP client switch has VLANs 1, 2, 3, 10, and 30 configured as part of a VTP domain; however, the switch has users connected only to access switch ports defined on VLANs 3 and 30. If VTP pruning is enabled and all VLANs are eligible, which VLANs will be pruned on the upstream switch?

2, 10

13.The VTP domain Area3 consists of one server and several clients. The server’s VTP configuration revision number is at 11. A new switch is added to the network. It has VTP domain name Area5, and a configuration revision number of 10. What will happen when the new switch is added to the network? What happens when the VTP domain name is changed to Area3 on the new switch?

Domain Area5 will experience no change when the switch is added. The two domains, Area3 and Area5, will coexist on the same network with different sets of clients. The configuration revision numbers on both servers will stay unchanged.

When the domain is changed to Area3, that domain will then have two VTP servers. The switch that has the newly configured domain name has a lower configuration revision number, so it will learn all VTP information from the existing server. The new switch’s revision number will become 11, and its list of defined VLANs will change to match the existing server.

14.What command will show information about the VTP configuration on a Catalyst 3550? show vtp status

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“Do I Know This Already?”

1.e

A maximum of 8 ports can be bundled, offering 8 × 200 Mbps (full-duplex), or 1600 Mbps.

2.c

3.c

4.d

5.c

6.c

7.a

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Q&A

1.What are some benefits of an EtherChannel? Increased bandwidth

Link redundancy

2.How many links can be aggregated into an EtherChannel? 2 to 8

3.Traffic between two hosts will be distributed across all links in an EtherChannel. True or false? Answer: False

4.Which methods can you use to distribute traffic in an EtherChannel? MAC address

IP address Layer 4 port

5.How does an EtherChannel distribute broadcasts and multicasts?

Broadcasts and multicasts are distributed across the links within an EtherChannel, just like any other traffic. The broadcast or multicast addresses are used in the hash or load-balancing algorithm to determine the link index.

6.When load balancing, what hashing functions choose a link for a frame?

If the hashing function is based on a single address (MAC, IP, or port), the low-order bits of that address are used as a link index. If two addresses or port numbers are used, the exclusive-OR (XOR) of those two values is used to derive the low-order bits that form a link index.

542Appendix A: Answers to Chapter “Do I Know This Already?” Quizzes and Q&A Sections

7.What protocols can negotiate an EtherChannel between two switches? PAgP

LACP

8.Suppose a switch at one end of an EtherChannel is configured to use source MAC addresses for load balancing. The switch on the other end is configured to use both source and destination IP addresses. What will happen?

The EtherChannel will successfully transport traffic between the two switches. However, the traffic load will not be distributed evenly or symmetrically across the links in the channel.

9.Two switches have a 4-port EtherChannel between them. Both switches are load balancing using source and destination IP addresses. If a packet has source address 192.168.15.10 and destination address 192.168.100.31, what is the EtherChannel link index?

The link index is computed by an XOR of the source and destination IP addresses. Because this is a 4-port link, only the two low-order bits are needed. 10 XOR 31 can be computed by using binary values: 00001010 XOR 00011111 = 00010101. The lowest two bits (01) give a link index of 1.

10.What does the acronym PAgP stand for? Port Aggregation Protocol

11.Two switches should be configured to negotiate an EtherChannel. If one switch is using PAgP “auto” mode, what should the other switch use?

PAgP “desirable” mode

12.What is the LACP system priority value used for?

The switch with the lowest system ID (system priority + MAC address) is allowed to make decisions regarding which ports will actively participate in an EtherChannel and which ones will be held in a standby state.

13.Complete the following command to put an interface into EtherChannel group 3, and to use PAgP to ask the far-end switch to participate in the EtherChannel. This switch port should also require PAgP packets back from the far-end switch.

Switch(config-if)# channel-group channel-group 3 mode desirable non-silent

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14.What interface configuration command is needed to select LACP as the EtherChannel negotiation protocol?

channel-protocol lacp

15.What command could you use to see the status of every port in an EtherChannel? show etherchannel summary

16.What command could you use to verify the hashing algorithm used for EtherChannel load balancing?

show etherchannel load-balance

17.Suppose a switch is used in a small data center where one server offers an IP-based application to many clients throughout the campus. An EtherChannel connects the data center switch to a Layer 3 core switch, which routes traffic to all clients. What EtherChannel load-balancing method might be most appropriate at the data center switch?

a.Source MAC address

b.Source IP address

c.Destination MAC address

d.Destination IP address

e.Source and destination MAC address

f.Source and destination IP address

Answer: d. Remember that the EtherChannel will only load balance outbound traffic, or that from the server toward the clients. Here are brief explanations of each of the choices to help clarify the answer.

a.Source MAC address—Not very useful. Because the source MAC address (the server) will always be the same. One link in the channel would always be selected.

b.Source IP address—Not very useful. Again, the source IP address (the server) is constant.

c.Destination MAC address—Not very useful. Because a Layer 3 switch is positioned in the core layer, it will always appear as the destination MAC address for all client destinations.

d.Destination IP address—This is the best choice because the destination IP addresses of the clients are diverse and not modified along the path.

544Appendix A: Answers to Chapter “Do I Know This Already?” Quizzes and Q&A Sections

e.Source and destination MAC address—Not very useful. Because the destination MAC address will always be the Layer 3 switch, only one link will be used.

f.Source and destination IP address—This would make a good choice, although the combination of addresses doesn’t add anything. The source IP address (the server) will always be constant. Therefore, source XOR destination will always yield something similar to the destination address itself.

18.Suppose a mainframe is connected to a switch that has an EtherChannel uplink to a campus network. The EtherChannel has been configured with the port-channel load-balance src-dst- ip command. Most of the mainframe traffic is SNA (non-IP). What will happen to the SNA frames when they are switched? Would it be better to reconfigure the channel with portchannel load-balance src-dst-mac?

The SNA frames are non-IP, so only MAC addresses are relevant. The switch has been configured to load balance according to the XOR of the source and destination IP addresses. Obviously, the SNA frames will have neither of these values present. The switch will realize this and fall back to the “lower” method of src-dst-mac (XOR of the source and destination MAC addresses) for each SNA frame. No configuration changes are necessary for this to occur.

There really isn’t a good reason to reconfigure for src-dst-mac because the switch is able to forward the SNA frames already. However, if it were reconfigured, any IP packets would be encapsulated in Ethernet frames, providing MAC addresses within the frames.

19.What attributes of a set of switch ports must match to form an EtherChannel? Port speed

Port duplex Trunking mode

Trunking encapsulation Access or native VLAN

20.What happens if one port of an EtherChannel is unplugged or goes dead? What happens when that port is reconnected?

Traffic on the disconnected port will be moved to the next available link in the EtherChannel bundle. When the port is reconnected, traffic will not automatically move back to the bundle’s original port. Rather, new traffic will be learned and applied to the restored link.