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CCNP 642-811 BCMSN Exam Certification Guide - Cisco press

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346 Chapter 14: Router Redundancy and Load Balancing

By default, any client from any IP address can make connections to the virtual server. To limit the access, define only the IP subnet or address range (with subnet mask) that is allowed access. The inverse-mask here resembles that of an access list, where a 1-bit ignores and a 0-bit matches.

Step 5 Put the virtual server into service:

Switch(config-slb-vserver)# inservice

By default, SLB does not allow connections to be made to a virtual server until it is put into service. If a virtual server needs to be temporarily disabled for some reason, use the no inservice command.

Verifying Redundancy and Load Balancing

To verify the operation of the features discussed in this chapter, you can use the commands listed in Table 14-3. In particular, look for the active router, standby or backup routers, and load-balancing methods in use.

Table 14-3 Redundancy and Load Balancing Verification Commands


Command Syntax







Show HSRP status.

show standby brief



Show HSRP on an interface.

show standby type mod/num



Show VRRP status.

show vrrp brief all



Show VRRP on an interface.

show vrrp interface type mod/num







Show status of a GLBP group.

show glbp group







Show server farms.

show ip slb serverfarms



Show real servers.

show ip slb reals



Show virtual servers.

show ip slb vserver



Show current SLB connections.

show ip slb conns



Foundation Summary 347

Foundation Summary

The Foundation Summary is a collection of information that provides a convenient review of many key concepts in this chapter. If you are already comfortable with the topics in this chapter, this summary can help you recall a few details. If you just read this chapter, this review should help solidify some key facts. If you are doing your final preparation before the exam, this information is a convenient way to review the day before the exam.

Table 14-4 A Comparison of Router Redundancy Protocols










no; Cisco-proprietary,

yes; RFC 2338

no; Cisco-proprietary


RFC 2281







Router roles

Active router, standby

Master router, backup










Load balancing

Only through multiple

Only through multiple

Inherent with one


HSRP groups, different

VRRP groups, different

GLBP group; all clients


client gateways

client gateways

use same gateway;




several methods









Interface tracking








Virtual router MAC



assigned by AVG









Table 14-5 HSRP Configuration Commands


Command Syntax



Set the HSRP priority.

standby group priority priority



Set the HSRP timers.

standby group timers hello holdtime



Allow router preemption.

standby group preempt [delay seconds]



Use group authentication.

standby group authentication string



Adjust priority by tracking an interface.

standby group track type mod/num decrementvalue



Assign the virtual router address.

standby group ip ip-address [secondary]



348 Chapter 14: Router Redundancy and Load Balancing

Table 14-6 VRRP Configuration Commands


Command Syntax



Assign a VRRP router priority (default 100).

vrrp group priority level



Alter the advertisement timer (default 1 second).

vrrp group timers advertise [msec] interval



Learn the advertisement interval from the master router.

vrrp group timers learn



Disable preempting (default is to preempt).

no vrrp group preempt



Change the preempt delay (default 0 seconds).

vrrp group preempt [delay seconds]



Use authentication for advertisements.

vrrp group authentication string



Assign a virtual IP address.

vrrp group ip ip-address [secondary]



Table 14-7 GLBP Configuration Commands


Command Syntax



Assign a GLBP priority.

glbp group priority level



Allow GLBP preemption.

glbp group preempt [delay minimum seconds]



Define an object to be

track object-number interface type mod/num {line-protocol | ip routing}





Define the weighting

glbp group weighting maximum [lower lower] [upper upper]





Track an object.

glbp group weighting track object-number [decrement value]



Choose the load-balancing

glbp group load-balancing [round-robin | weighted | host-dependent]





Assign a virtual router

glbp group ip [ip-address [secondary]]







Foundation Summary 349

Table 14-8 SLB Configuration Commands







Command Syntax





Name a server farm.

ip slb serverfarm serverfarm-name





Choose a load-balancing method.

predictor {roundrobin | leastconns}





Identify a real server.

real ip-address





Assign a relative weight to the real server.

weight weighting-value





Enable the server for use.






Name the virtual server.

ip slb vserver virtual-server-name





Link the virtual server to a server farm.

serverfarm serverfarm-name





Limit access to the virtual server.

client ip-address network-mask





Define the virtual server IP address.

virtual ip-address





Enable the virtual server for use.





350 Chapter 14: Router Redundancy and Load Balancing


The questions and scenarios in this book are more difficult than what you should experience on the actual exam. The questions do not attempt to cover more breadth or depth than the exam; however, they are designed to make sure that you know the answer. Rather than allowing you to derive the answers from clues hidden inside the questions themselves, the questions challenge your understanding and recall of the subject. Hopefully, these questions will help limit the number of exam questions on which you narrow your choices to two options and then guess.

You can find the answers to these questions in Appendix A.

1.A multilayer switch has been configured with the command standby 5 priority 120. What router redundancy protocol is being used?

2.What feature can you use to prevent other routers from accidentally participating in an HSRP group?

3.What command can configure an HSRP group to use a virtual router address of

4.The show standby vlan 271 command produces the following output:

Vlan271 - Group 1

Local state is Active, priority 210, may preempt

Hellotime 3 holdtime 40 configured hellotime 3 sec holdtime 40 sec Next hello sent in 00:00:00.594

Virtual IP address is configured Secondary virtual IP address Secondary virtual IP address

Active router is local

Standby router is unknown expires in 00:00:37 Standby virtual mac address is 0000.0c07.ac01 2 state changes, last state change 5d17h

If the local router fails, which router takes over the active role for the virtual router address

5.What is meant by preempting in HSRP?

6.What protocols discussed in this chapter support interface tracking?

Q&A 351

7.The show standby brief command has been used to check the status of all HSRP groups on the local router. The output from this command is as follows:

Switch# show standby brief

P indicates configured to preempt.











P State

Active addr

Standby addr

Group addr




P Active





P Active





P Active


Each interface is shown to have Group 1. Is this a problem?

8.How many HSRP groups are needed to load balance traffic over two routers?

9.What load-balancing methods can GLBP use?

10.What command can you use to see the status of the active and standby routers on the VLAN 171 interface?

11.How many GLBP groups are needed to load balance traffic over four routers?

12.When should you use SLB?

13.What command defines and names an SLB server farm?

14.A virtual server has just been defined with the following commands:

ip slb vserver CISCO serverfarm CISCO-FARM virtual

Can the virtual server be used immediately? If not, what additional command is needed?

This chapter covers the following topics that you need to master for the CCNP BCMSN exam:

Multicast Overview—This section discusses multicast addressing and general multicast traffic forwarding.

Routing Multicast Traffic—This section covers the protocols used by Layer 3 devices to maintain multicast groups and their members, and to constrain multicast forwarding.

Switching Multicast Traffic—This section explains techniques that you can use to intelligently forward multicast traffic at Layer 2.

Verifying Multicast—This section provides a brief summary of the commands that can verify the configuration and operation of multicast routing and switching.

C H A P T E R 15


Multicast traffic is typically sent by one source and received by a group of recipients, spread throughout a network and changing over time. Examples of multicast traffic include video streams for instruction or entertainment, certain audio conference calls, and one-to-many PC file imaging applications.

Because not everyone on a network wants to receive the traffic from a multicast source, switches and routers must have some means to forward traffic to exactly the destinations that want to receive it. This chapter covers IP multicast and the various protocols used to forward multicast packets.

“Do I Know This Already?” Quiz

The purpose of the “Do I Know This Already?” quiz is to help you decide what parts of this chapter to use. If you already intend to read the entire chapter, you do not necessarily need to answer these questions now.

The quiz, derived from the major sections in the “Foundation Topics” portion of the chapter, helps you determine how to spend your limited study time.

Table 15-1 outlines the major topics discussed in this chapter and the “Do I Know This Already?” quiz questions that correspond to those topics.

Table 15-1 “Do I Know This Already?” Foundation Topics Section-to-Question Mapping

Foundation Topics Section

Questions Covered in This Section



Multicast Overview




Routing Multicast Traffic




Switching Multicast Traffic




354 Chapter 15: Multicast

CAUTION The goal of self-assessment is to gauge your mastery of the topics in this chapter. If you do not know the answer to a question or are only partially sure of the answer, you should mark this question wrong. Giving yourself credit for an answer you correctly guess skews your selfassessment results and might give you a false sense of security.

1.How many sources are typically present in a multicast group?



c.As many as are registered with the router

d.Cannot be determined

2.Which one of the following is a multicast address?




d. corresponds to which of the following MAC addresses?





4.How many unique multicast IP addresses can correspond to one multicast MAC address?





“Do I Know This Already?” Quiz 355

5.Which of the following is the test that is performed before a multicast packet can be forwarded?

a.Shortest Path First

b.Cyclic Redundancy Check

c.Reverse Path Forwarding

d.Multicast Route Verification

6.Which protocol registers hosts for multicast group membership?





7.A host sends Internet Group Management Protocol (IGMP) packets to which of the following?

a.The local switch

b.The local router

c.The multicast source

d.The root of the multicast tree

8.If a multicast group has recipients on every subnet, which of the PIM modes should be used?

a.Dense mode

b.Sparse mode

c.Sparse-compress mode

d.Flood mode

9.Which type of tree structure is built for sparse mode multicast routing?

a.Spanning Tree

b.Shared Tree

c.Sparse Tree

d.Simple Tree

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