Search in book...
Toggle Font Controls
Create new playlist

Name your new playlist

Playlist description (optional)
Sign In

Email address

Password

Forgot Password?

or

Continue with Facebook

Continue with Google
Sign Up

Full Name

Email address

Confirm Email Address

Password

or

Continue with Facebook

Continue with Google

Appendix A. Answers to Review Questions

Chapter 1

1.	What is a converged network?
Answer:	A converged network is one in which data, voice, and video traffic coexists on a single network.
2.	What are the three phases of the IIN?
Answer:	Integrated transport, integrated services, and integrated applications
3.	Which are layers within the SONA framework? Access Network Infrastructure Interactive Services Enterprise Edge Application Edge Distribution
Answer:	b, c, e
4.	What are the components of the Cisco Enterprise Architecture?
Answer:	Campus, data center, branches, teleworkers, and WAN
5.	Which are the layers within the hierarchical network model? Access Network Infrastructure Core Distribution Application Edge Distribution Network Management
Answer:	a, c, d
6.	Describe each of the functional areas of the Enterprise Composite Network Model.
Answer:	The Enterprise Composite Network Model first divides the network into three functional areas, as follows: Enterprise Campus—. This functional area contains the modules required to build a hierarchical, highly robust campus network. Enterprise Edge—. This functional area aggregates connectivity from the various elements at the edge of the enterprise network, including to remote locations, the Internet, and remote users. Service Provider Edge—. This area is not implemented by the organization; instead, it is included to represent connectivity to service providers.
7.	Which modules are within the Enterprise Campus functional area?
Answer:	The Enterprise Campus functional area comprises the following modules: Building, Building Distribution, Core (also called the backbone), Edge Distribution, Server, and Management.
8.	Why might a network need to have more than one routing protocol running?
Answer:	Each part of the network might have different routing protocol requirements. For example, BGP might be required in the Corporate Internet module, whereas static routes are often used for remote-access and VPN users. Therefore, enterprises might have to run multiple routing protocols.

Chapter 2

1.	Which of the following is not a scenario in which static routes would be used? When the administrator needs total control over the routes used by the router When a backup to a dynamically recognized route is necessary When rapid convergence is needed When a route should appear to the router as a directly connected network
Answer:	c. Note that Answer d refers to the situation when a static route is configured and the interface parameter is used, specifying the local router outbound interface to use to reach the destination network. The router considers this a directly connected route, and the default administrative distance is 0.
2.	What are two drawbacks of static routes? Reconfiguring to reflect topology changes Complex metrics Involved convergence Absence of dynamic route discovery
Answer:	a, d
3.	What is used by traffic for which the destination network is not specifically listed in the routing table? Dynamic area Default route Border gateway Black hole
Answer:	b
4.	The show ip route command usually provides information on which of the following two items? Next hop Metric CDP Hostname
Answer:	a, b
5.	When using dynamic routing protocols, what does the administrator configure the routing protocol on? Each area Each intermediate system Each router Each gateway of last resort
Answer:	c
6.	Which of the following is not a dynamic routing protocol? IS-IS CDP EIGRP BGP RIPv2
Answer:	b
7.	What is a metric? A standard of measurement used by routing algorithms The set of techniques used to manage network resources Interdomain routing in TCP/IP networks Services limiting the input or output transmission rate
Answer:	a
8.	Which routing protocol uses only major classful networks to determine the interfaces participating in the protocol? EIGRP RIPv1 IS-IS BGP OSPF
Answer:	b
9.	ODR uses what to carry network information between spoke (stub) routers and the hub? Metric BGP Convergence CDP
Answer:	d
10.	Which of the following is not a classification of routing protocols? Link-state Default Hybrid Distance vector
Answer:	b
11.	What do you call the process when a router, using a classful routing protocol, sends an update about a subnet of a classful network across an interface belonging to a different classful network and assumes that the remote router will use the default subnet mask for that class of IP address? Autosummarization Default routing Classful switching Tunneling
Answer:	a
12.	True or false: Discontiguous subnets are subnets of the same major network that are separated by a different major network.
Answer:	True
13.	Classless routing protocols allow __________. QoS VLSM VPN RIP
Answer:	b
14.	What is the command to turn off autosummarization? no auto-summarization enable classless ip route no auto-summary
Answer:	d
15.	What is the OSPF default administrative distance value? 90 100 110 120
Answer:	c
16.	When a static route’s administrative distance is manually configured to be higher than the default administrative distance of dynamic routing protocols, that static route is called what? Semistatic route Floating static route Semidynamic route Manual route
Answer:	b
17.	Which variables can be used to calculate metrics? Hops Convergence time Administrative distance Path attributes Cost
Answer:	a, d, e

Chapter 3

What are some features of EIGRP?

Answer:

Features of EIGRP include fast convergence, VLSM support, partial updates, multiple network layer support, seamless connectivity across all data-link protocols and topologies, sophisticated metric, and use of multicast and unicast.

Is EIGRP operational traffic multicast or broadcast?

Answer:

EIGRP operational traffic is multicast (and unicast).

What are the four key technologies employed by EIGRP?

Answer:

The four key technologies are: neighbor discovery/recovery mechanism, Reliable Transport Protocol (RTP), Diffusing Update Algorithm (DUAL) finite state machine, and protocol-dependent modules.

How do IGRP and EIGRP differ in their metric calculation?

Answer:

IGRP and EIGRP use the same algorithm for metric calculation, but EIGRP’s metric value is multiplied by 256 to provide it more granular decision-making. EIGRP represents its metrics in 32-bit format instead of the 24-bit representation used by IGRP.

Which of the following best describes the EIGRP topology table?

It is populated as a result of receiving hello packets.
It contains all learned routes to a destination.
It contains only the best routes to a destination.

Answer:

Describe the five types of EIGRP packets.

Answer:

EIGRP uses the following five types of packets:

Hello—Hello packets are used for neighbor discovery. They are sent as multicasts and carry an acknowledgment number of 0.
Update—Update packets contain route change information. An update is sent to communicate the routes a particular router has used to converge; an update is sent only to affected routers. These updates are sent as multicasts when a new route is discovered and when convergence is completed (when the route becomes passive). To synchronize topology tables, updates are sent as unicasts to neighbors during their EIGRP startup sequence. Updates are sent reliably.
Query—When a router is performing route computation and does not find a feasible successor, it sends a query packet to its neighbors, asking if they have a successor to the destination. Queries are normally multicast but can be retransmitted as unicast packets in certain cases; they are sent reliably.
Reply—A reply packet is sent in response to a query packet. Replies are unicast to the originator of the query and are sent reliably.
Acknowledge (ACK)—The ACK is used to acknowledge updates, queries, and replies. ACK packets are unicast hello packets and contain a nonzero acknowledgment number. (Note that hello and ACK packets do not require acknowledgment.)

True or false: EIGRP hello packets are sent every 5 seconds on LAN links.

Answer:

True.

What is the difference between the hold time and the hello interval?

Answer:

The hello interval determines how often hello packets are sent. It is 5 or 60 seconds by default, depending on the media type.

The hold time is the amount of time a router considers a neighbor up without receiving a hello or some other EIGRP packet from that neighbor. Hello packets include the hold time. The hold time interval is set by default to 3 times the hello interval.

Which of the following statements are true?

A route is considered passive when the router is not performing recomputation on that route.
A route is passive when it is undergoing recomputation.
A route is active when it is undergoing recomputation.
A route is considered active when the router is not performing recomputation on that route.
Passive is the operational state for a route.
Active is the operational state for a route.

Answer:

a, c, e

10.

Which command is used to see the RTO and hold time?

show ip eigrp traffic
show ip eigrp timers
show ip eigrp route
show ip eigrp neighbors

Answer:

11.

Why are EIGRP routing updates described as reliable?

Answer:

EIGRP update packets are generated by the Reliable Transport Protocol (RTP) within EIGRP. Reliable packets have a sequence number assigned to them, and the receiving device must acknowledge them.

12.

What units are the bandwidth and delay parameters in the EIGRP metric calculation?

Answer:

The default formula for the EIGRP metric is metric = bandwidth + delay.

In this formula, the EIGRP delay value is the sum of the delays in the path, in tens of microseconds, multiplied by 256.

The bandwidth is calculated using the minimum bandwidth link along the path, represented in kbps. 10⁷ is divided by this value, and then the result is multiplied by 256.

13.

Which of the following statements are true regarding AD and FD?

The AD is the EIGRP metric for a neighbor router to reach a particular network.
The AD is the EIGRP metric for this router to reach a particular network.
The FD is the EIGRP metric for this router to reach a particular network.
The FD is the EIGRP metric for the neighbor router to reach a particular network.

Answer:

a, c

14.

What does it mean when a route is marked as an FS?

Answer:

A feasible successor (FS) is a router providing a backup route. The route through the feasible successor must be loop free; in other words, it must not loop back to the current successor. To qualify as an FS, a next-hop router must have an advertised distance less than the feasible distance of the current successor route for the particular network.

15.

In the following table, place the letter of the description next to the term the description describes. The descriptions may be used more than once.

Descriptions:

A network protocol that EIGRP supports.
A table that contains FS information.
The administrative distance determines routing information that is included in this table.
A neighbor router that has the best path to a destination.
A neighbor router that has a loop-free alternative path to a destination.
An algorithm used by EIGRP that ensures fast convergence.
A multicast packet used to discover neighbors.
A packet sent by EIGRP routers when a new neighbor is discovered and when a change occurs.

Answer:

Term	Description Letter
Successor	d
Feasible successor	e
Hello	g
Topology table	b
IP	a
Update	h
AppleTalk	a
Routing table	c
DUAL	f
IPX	a

16.

Answer true or false to the following statements.

Answer:

EIGRP performs autosummarization. True

EIGRP autosummarization cannot be turned off. False

EIGRP supports VLSM. True

EIGRP can maintain three independent routing tables. True

The EIGRP hello interval is an unchangeable fixed value. False

17.

Which of the following are true?

For Frame Relay point-to-point interfaces, set the bandwidth to the CIR.
For Frame Relay point-to-point interfaces set the bandwidth to the sum of all CIRs.
For Frame Relay multipoint connections, set the bandwidth to the sum of all CIRs.
For generic serial interfaces such as PPP and HDLC, set the bandwidth to match the line speed.
For Frame Relay multipoint connections, set the bandwidth to the CIR.

Answer:

a, c, d

18.

Router A has three interfaces with IP addresses 172.16.1.1/24, 172.16.2.3/24, and 172.16.5.1/24. What commands would be used to configure EIGRP to run in autonomous system 100 on only the interfaces with addresses 172.16.2.3/24 and 172.16.5.1/24?

Answer:

One EIGRP configuration for Router A is as follows:

       RouterA(config)#router eigrp 100
       RouterA(config-router)#network 172.16.2.0 0.0.0.255
       RouterA(config-router)#network 172.16.5.0 0.0.0.255

19.

Routers A and B are connected and are running EIGRP on all their interfaces. Router A has four interfaces, with IP addresses 172.16.1.1/24, 172.16.2.3/24, 172.16.5.1/24, and 10.1.1.1/24. Router B has two interfaces, with IP addresses 172.16.1.2/24 and 192.168.1.1/24. There are other routers in the network that are connected on each of the interfaces of these two routers that are also running EIGRP. Which summary routes does Router A generate automatically?

172.16.0.0/16
192.168.1.0/24
10.0.0.0/8
172.16.1.0/22
10.1.1.0/24

Answer:

a, c

20.

Router A has four EIGRP paths to a destination with the following EIGRP metrics. Assuming no potential routing loops exist and the command variance 3 is configured on Router A, which paths are included for load balancing?

Path 1: 1100
Path 2: 1200
Path 3: 2000
Path 4: 4000

Answer:

a, b, c

21.

Router A has the following configuration:

        interface s0
          ip bandwidth-percent eigrp 100 40
          bandwidth 256
        router eigrp 100
          network 10.0.0.0

What is the maximum bandwidth that EIGRP uses on the S0 interface?

Answer:

22.

What is the default EIGRP authentication?

Simple password
MD5
None
IPsec

Answer:

23.

True or false: When configuring EIGRP authentication, each router must have a unique password configured.

Answer:

False

24.

What does the accept-lifetime command do for EIGRP authentication?

Answer:

This command specifies the time period during which the key will be accepted for use on received packets.

25.

What command is used to troubleshoot EIGRP authentication?

debug eigrp authentication
debug ip eigrp packets
debug eigrp packets
debug ip eigrp authentication

Answer:

26.

What is the default EIGRP stuck-in-active timer?

Answer:

The default EIGRP stuck-in-active timer is 3 minutes. If the router does not receive a reply to all the outstanding queries within this time, the route goes to the stuck-in-active state, and the router resets the neighbor relationships for the neighbors that failed to reply.

27.

With the EIGRP active process enhancement, when does the SIA-Query get sent?

Answer:

The SIA-Query is sent at the midway point of the active timer (one and a half minutes by default).

28.

How does EIGRP summarization limit the query range?

Answer:

Summarization limits the query range because a remote router extends the query about a network only if it has an exact match in the routing table.

29.

How does the EIGRP stub feature limit the query range?

Answer:

Stub routers are not queried. Instead, hub routers connected to the stub router answer the query on behalf of the stub router.

30.

What does the eigrp stub receive-only command do?

Answer:

This command makes the router an EIGRP stub; the receive-only keyword restricts the router from sharing any of its routes with any other router within the EIGRP autonomous system.

31.

True or false: Goodbye messages are sent in hello packets.

Answer:

True.

32.

The following is part of the output of the show ip eigrp topology command:

P 10.1.3.0/24, 1 successors, FD is 10514432
         via 10.1.2.2 (10514432/28160), Serial0/0/0

What are the two numbers in parentheses?

Answer:

The first number is the feasible distance for the network through the next-hop router, and the second number is the advertised distance from the next-hop router to the destination network.

Chapter 4

1.	Which of the following is not a characteristic of link-state routing protocols? They respond quickly to network changes. They broadcast every 30 minutes. They send triggered updates when a network change occurs. They may send periodic updates, known as link-state refresh, at long time intervals, such as every 30 minutes.
Answer:	b
2.	For all the routers in the network to make consistent routing decisions, each link-state router must keep a record of all the following items except which one? Its immediate neighbor routers All of the other routers in the network, or in its area of the network, and their attached networks The best paths to each destination The version of the routing protocol used
Answer:	d
3.	Link-state routing protocols use a two-layer area hierarchy composed of which two areas? Transit area Transmit area Regular area Linking area
Answer:	a, c
4.	Which of the following is not a characteristic of an OSPF area? It may minimize routing table entries. It requires a flat network design. It may localize the impact of a topology change within an area. It may stop detailed LSA flooding at the area boundary.
Answer:	b
5.	True or false: An ABR connects area 0 to the nonbackbone areas.
Answer:	True
6.	When a router receives an LSA (within an LSU), it does not do which of the following? If the LSA entry does not already exist, the router adds the entry to its LSDB, sends back an LSAck, floods the information to other routers, runs SPF, and updates its routing table. If the entry already exists and the received LSA has the same sequence number, the router overwrites the information in the LSDB with the new LSA entry. If the entry already exists but the LSA includes newer information (it has a higher sequence number), the router adds the entry to its LSDB, sends back an LSAck, floods the information to other routers, runs SPF, and updates its routing table. If the entry already exists but the LSA includes older information, it sends an LSU to the sender with its newer information.
Answer:	b
7.	What is an OSPF type 2 packet? Database description (DBD), which checks for database synchronization between routers Link-state request (LSR), which requests specific link-state records from router to router Link-state update (LSU), which sends specifically requested link-state records Link-state acknowledgment (LSAck), which acknowledges the other packet types
Answer:	a
8.	Which of the following is true of hellos and dead intervals? They do not need to be the same on neighboring routers, because the lowest common denominator is adopted. They do not need to be the same on neighboring routers, because the highest common denominator is adopted. They do not need to be the same on neighboring routers, because it is a negotiated interval between neighboring routers. They need to be the same on neighboring routers.
Answer:	d
9.	Which IP address is used to send an updated LSA entry to OSPF DRs and BDRs? Unicast 224.0.0.5 Unicast 224.0.0.6 Multicast 224.0.0.5 Multicast 224.0.0.6
Answer:	d
10.	To ensure an accurate database, how often does OSPF flood (refresh) each LSA record? Every 60 minutes. Every 30 minutes. Every 60 seconds. Every 30 seconds. Flooding each LSA record would defeat the purpose of a link-state routing protocol, which strives to reduce the amount of routing traffic it generates.
Answer:	b
11.	What command is used to display the router ID, timers, and statistics? show ip ospf show ip ospf neighbors show ip ospf stats show ip ospf neighborship
Answer:	a
12.	Which of the following is not a way in which the OSPF router ID (a unique IP address) can be assigned? The highest IP address of any physical interface The lowest IP address of any physical interface The IP address of a loopback interface The router-id command
Answer:	b
13.	True or false: On point-to-point networks, the router dynamically detects its neighboring routers by multicasting its hello packets to all SPF routers using the address 224.0.0.6.
Answer:	False
14.	An adjacency is the relationship that exists where? Between routers located on the same physical network Between routers in different OSPF areas Between a router and its DR and BDR on different networks Between a backbone DR and a transit BDR
Answer:	a
15.	Which of the following is not true regarding the OSPF DR/BDR election? The router with the highest priority value is the DR. The router with the second-highest priority value is the BDR. If all routers have the default priority, the router with the lowest router ID becomes the DR. The router with a priority set to 0 cannot become the DR or BDR.
Answer:	c
16.	Which of the following is not true of OSPF point-to-multipoint mode? It does not require a full-mesh network. It does not require a static neighbor configuration. It uses multiple IP subnets. It duplicates LSA packets.
Answer:	c
17.	What is the default OSPF mode on a point-to-point Frame Relay subinterface? Point-to-point mode Multipoint mode Nonbroadcast mode Broadcast mode
Answer:	a
18.	What is the default OSPF mode on a Frame Relay multipoint subinterface? Point-to-point mode Multipoint mode Nonbroadcast mode Broadcast mode
Answer:	c
19.	What is the default OSPF mode on a main Frame Relay interface? Point-to-point mode Multipoint mode Nonbroadcast mode Broadcast mode
Answer:	c

Chapter 5

True or false: OSPF performs route summarization by default.

Answer:

False

True or false: In a large network where topological changes are frequent, routers spend many CPU cycles recalculating the SPF algorithm and updating the routing table.

Answer:

True

Match the type of router with its description:

Type of Router	Description
1—Internal router	A—A router that sits in the perimeter of the backbone area and that has at least one interface connected to area 0. It maintains OSPF routing information using the same procedures and algorithms as an internal router.
2—Backbone router	B—A router that has interfaces attached to multiple areas, maintains separate LSDBs for each area to which it connects, and routes traffic destined for or arriving from other areas. This router is an exit point for the area, which means that routing information destined for another area can get there only via the local area’s router of this type. This kind of router can be configured to summarize the routing information from the LSDBs of its attached areas. This router distributes the routing information into the backbone.
3—ABR	C—A router that has all its interfaces in the same area.
4—ASBR	D—A router that has at least one interface attached to an external internetwork (another AS), such as a non-OSPF network. This router can import non-OSPF network information to the OSPF network and vice versa; this process is called route redistribution.

Answer:

1—C
2—A
3—B
4—D

How many different types of LSAs are there?

Answer:

What kind of router generates LSA type 5?

DR
ABR
ASBR
ADR

Answer:

True or false: By default, OSPF does not automatically summarize groups of contiguous subnets.

Answer:

True

Where does a type 1 LSA flood to?

To immediate peers
To all other routers in the area where it originated
To routers located in other areas
To all areas

Answer:

How does a routing table reflect the link-state information of an intra-area route?

The route is marked with O.
The route is marked with I.
The route is marked with IO.
The route is marked with EA.
The route is marked with O IA.

Answer:

Which type of external route is the default?

E1.
E2.
E5.
There is no default external route. OSPF adapts and chooses the most accurate one.

Answer:

10.

E1 external routes calculate the cost by adding what?

The internal cost of each link the packet crosses
The external cost to the internal cost of each link the packet crosses
The external cost only
All area costs, even those that are not used

Answer:

11.

What does the OSPF max-lsa command do?

Defines the maximum number of LSAs that the router can generate
Protects the router from an excessive number of received (non-self-generated) LSAs in its LSDB
Defines the maximum size of the LSAs that the router generates
Protects the router from excessively large received (non-self-generated) LSAs in its LSDB

Answer:

12.

How is the OSPF metric calculated, by default?

OSPF calculates the OSPF metric for a router according to the bandwidth of all its interfaces.
OSPF calculates the OSPF metric by referencing the DR.
OSPF calculates the OSPF metric for an interface according to the interface’s inverse bandwidth.
OSPF calculates the OSPF metric by using the lowest bandwidth value among all of its interfaces.

Answer:

13.

Why is configuring a stub area advantageous?

It reduces the size of the LSDB inside an area.
It increases the memory requirements for routers in that area.
It further segments the hierarchy.
It starts to behave like a distance vector routing protocol, thus speeding up convergence.

Answer:

14.

A stub area is typically created using what kind of topology?

Point to point
Broadcast
Hub and spoke
Full mesh

Answer:

15.

True or false: By default, in standard areas, routers generate default routes.

Answer:

False

16.

What command makes an OSPF router generate a default route?

ospf default-initiate
default-information originate
default information-initiate
ospf information-originate

Answer:

17.

If your router has an interface faster than 100 Mbps that is used with OSPF, consider using the ____________ command under the ____________ process.

auto-cost reference-bandwidth, OSPF
auto-cost reference-bandwidth, interface
autocost reference-speed, OSPF
autocost reference-speed, interface

Answer:

18.

True or false: OSPF design requires that all areas be directly connect to the backbone.

Answer:

True

19.

True or false: Virtual links are very useful, and you should include them in your network architecture when designing a completely new OSPF network.

Answer:

False

20.

Which of the following would result in the smallest routing tables on OSPF internal routers?

Stub area
Totally stubby area
Standard area
Transit area

Answer:

21.

What is the default OSPF authentication?

Simple password
MD5
Null
IPsec

Answer:

22.

True or false: When configuring OSPF authentication, each router must have a unique password configured.

Answer:

False

23.

What command is used to troubleshoot OSPF authentication?

debug ip ospf adj
debug ip ospf auth
debug ip ospf md5
debug ip ospf packet

Answer:

24.

True or false: Only one MD5 OSPF authentication key can be configured at a time on a Cisco router.

Answer:

False

Chapter 6

1.	Which of the following does Integrated IS-IS support? BGP IP OSPF IPX
Answer:	b
2.	What is an IS? What is an ES?
Answer:	An IS is a router. An ES is a host.
3.	Because IS-IS is protocol independent, it can support which of the following? IPv4 IPv6 OSI CLNS All of the above
Answer:	d
4.	IS-IS routers use what to establish and maintain neighbor relationships? OSHs IIHs ISKs CLHs
Answer:	b
5.	As soon as neighbor adjacency is established, IS-IS routers exchange link-state information using what? Link-state packets Logical state packets Adjacency state packets Reachability state packets
Answer:	a
6.	Describe the four OSI routing levels.
Answer:	The following are the OSI routing levels: Level 0 routing is conducted by ES-IS. Level 1 and Level 2 routing are functions of IS-IS. The Interdomain Routing Protocol (IDRP) conducts Level 3 routing; Cisco routers do not support IDRP.
7.	What are some of the similarities between OSPF and IS-IS?
Answer:	The OSPF and IS-IS routing protocols have the following characteristics: They are open standard link-state routing protocols. They support VLSM. They use similar mechanisms (link-state advertisements [LSAs], link-state aging timers, and link-state database synchronization) to maintain the health of the LSDB. They use the shortest path first (SPF) algorithm, with similar update, decision, and flooding processes. They are successful in the largest and most demanding deployments (Internet Service Provider [ISP] networks). They converge quickly after network changes.
8.	What are CLNS addresses used by routers called? DSAPs NOTs MSAPs NETs
Answer:	d
9.	What are NSAP addresses equivalent to? A combination of the IP address and upper-layer protocol in an IP header Layer 2 addresses A combination of the transport layer address and data link address Layer 4 addresses
Answer:	a
10.	The Cisco implementation of Integrated IS-IS divides the NSAP address into what three fields? The data-link address, the logical address, and the upper-layer address The PDU address, the NSAP selector, and the cluster ID The area address, the system ID, and the NSAP selector The transport layer address, the CPU ID, and the NSAP selector
Answer:	c
11.	True or false: Cisco routers routing CLNS data do not use addressing that conforms to the ISO 10589 standard.
Answer:	False
12.	What is the first part of a NET? Zone address Area address Cluster address ISO address
Answer:	b
13.	How does an IS-IS L1/L2 router route a packet?
Answer:	An L1 IS sends a packet to the nearest L1/L2 IS. The L1/L2 IS routes by area address to other L1/L2 or L2 ISs. Forwarding through L1/L2 or L2 ISs, by area address, continues until the packet reaches an L1/L2 or L2 IS in the destination area. Within the destination area, ISs forward the packet along the best path, routing by system ID, until the destination ES is reached.
14.	What kind of IS-IS router is aware of only the local area topology? External Level 2 Internal Level 1
Answer:	d
15.	Routing between IS-IS areas is based on what? Area address IP address Level 2 Level 1/Level 2
Answer:	a
16.	True or false: In IS-IS, area boundaries fall on the links.
Answer:	True
17.	True or false: Symmetrical routing is a feature of IS-IS.
Answer:	False
18.	What does the IS-IS route leaking feature do?
Answer:	Route leaking helps reduce sub-optimal routing by providing a mechanism for leaking, or redistributing, L2 information into L1 areas. By having more detail about interarea routes, a L1 router is able to make a better choice with regard to which L1/L2 router to forward the packet.
19.	In IS-IS, PDUs are encapsulated directly into an OSI data-link frame, so there is no what? ISO or area address header CLNP or IP header ES or IP header CLNS or area address header
Answer:	b
20.	Cisco IOS Software automatically uses IS-IS broadcast mode for which two of the following? Dialer interfaces LAN interfaces Multipoint WAN interfaces Point-to-point subinterfaces
Answer:	b, c
21.	True or false: IS-IS offers support specifically for NBMA networks.
Answer:	False
22.	In IS-IS, rather than having each router connected to a LAN advertise an adjacency with every other router on the LAN, each router just advertises a single adjacency to what? Area Cluster LSDB Pseudo-node
Answer:	d
23.	True or false: IS-IS maintains the L1 and L2 LSPs in different LSDBs.
Answer:	True
24.	True or false: CSNPs are periodically sent on point-to-point links.
Answer:	False
25.	When configuring Integrated IS-IS for IP, which command is required to be configured on an interface? ip router net router isis net ip router isis ip isis router
Answer:	c
26.	What is the default IS-IS metric on an interface of a Cisco router? How can this be changed?
Answer:	The default IS-IS interface metric is 10. To change the metric value, use the isis metric metric [delay-metric [expense-metric [error-metric]]] {level-1 \| level-2} interface configuration command. Alternately, the metric default-value {level-1 \| level-2} router configuration command can be used to change the metric value for all IS-IS interfaces.
27.	What does “i L2” indicate in the output of the show ip route isis command?
Answer:	The show ip route isis command displays the IS-IS routes in the IP routing table. The i L2 tag indicates that the route was learned by IS-IS and it is from Level 2.
28.	What is a subnetwork point of attachment (SNPA)?
Answer:	The SNPA is the point that provides subnetwork services. SNPA is the equivalent of the Layer 2 address corresponding to the NET or NSAP address. The SNPA is assigned by using one of the following: The MAC address on a LAN interface. The virtual circuit ID from X.25 or ATM connections, or the data-link connection identifier (DLCI) from Frame Relay connections. For High-Level Data Link Control (HDLC) interfaces, the SNPA is simply set to “HDLC.”

Chapter 7

What are some of the things you need to consider when migrating to another routing protocol?

Answer:

An accurate topology map of the network and an inventory of all network devices

A hierarchical network structure

A redistribution strategy

A new addressing scheme and address summarization

List some things you may need to consider when transitioning to a new IP addressing plan.

Answer:

Host addressing

Access lists and other filters

NAT

DNS

Timing and transition strategy

A router is configured with a primary and secondary address on its FastEthernet 0/0 interface. It is also configured to run EIGRP on this interface. How will the secondary address interact with EIGRP?

Answer:

EIGRP uses an interface’s primary IP address as the source of its updates, and it expects the routers on both sides of a link to belong to the same subnet. Therefore, EIGRP will not use the secondary address on the interface.

What steps are involved when migrating to a new routing protocol?

Answer:

Create a clear and comprehensive timeline for all the steps in the migration, including implementing and testing the new router configurations.
Determine which routing protocol is the core and which is the edge.
Identify the boundary routers where the multiple routing protocols will run.
Determine how you want to redistribute information between the core and edge routing protocols.
Verify that all devices support the new routing protocol.
Implement and test the routing solution in a lab environment.

List some reasons why you might use multiple routing protocols in a network.

Answer:

When you are migrating from an older IGP to a new IGP, multiple redistribution boundaries might exist until the new protocol has displaced the old protocol completely.

You want to use another protocol, but you need to keep the old protocol because of the host systems’ needs.

Different departments might not want to upgrade their routers to support a new routing protocol.

If you have a mixed-router vendor environment, you can use a Cisco-specific protocol in the Cisco portion of the network and use a common standards-based routing protocol to communicate with non-Cisco devices.

What is redistribution?

Answer:

Cisco routers allow internetworks using different routing protocols (referred to as routing domains or autonomous systems) to exchange routing information through a feature called route redistribution. Redistribution is defined as the capability of boundary routers connecting different routing domains to exchange and advertise routing information between those routing domains (autonomous systems).

Does redistributing between two routing protocols change the routing table on the router that is doing the redistribution?

Answer:

No. Redistribution is always performed outbound. The router doing the redistribution does not change its routing table.

What are some issues that arise with redistribution?

Answer:

The key issues that may arise with redistribution are routing loops, incompatible routing information, and inconsistent convergence times.

What may be the cause of a routing loop in a network that has redundant paths between two routing processes?

Answer:

Depending on how you employ redistribution, routers might send routing information received from one autonomous system back into that same autonomous system. The feedback is similar to the routing loop problem that occurs with distance vector protocols.

10.

What two parameters do routers use to select the best path when they learn two or more routes to the same destination from different routing protocols?

Answer:

Each routing protocol is prioritized in order from most to least believable (reliable) using a value called administrative distance. This criterion is the first thing a router uses to determine which routing protocol to believe if more than one protocol provides route information for the same destination.

The routing metric is a value representing the path between the local router and the destination network, according to the routing protocol being used. The metric is used to determine the routing protocol’s “best” path to the destination.

11.

Fill in the default administrative distances for the following routing protocols.

Answer:

Routing Protocols	Default Administrative Distance Value
Connected interface	0
Static route out an interface	0
Static route to a next-hop address	1
EIGRP summary route	5
External BGP	20
Internal EIGRP	90
IGRP	100
OSPF	110
IS-IS	115
RIPv1 and RIPv2	120
EGP	140
ODR	160
External EIGRP	170
Internal BGP	200
Unknown	255

12.

When configuring a default metric for redistributed routes, should the metric be set to a value larger or smaller than the largest metric within the receiving autonomous system?

Answer:

When configuring a default metric for redistributed routes, set the metric to a value larger than the largest metric within the receiving autonomous system.

13.

Fill in the default seed metrics for the following protocols.

Answer:

Protocol That the Route Is Redistributed Into	Default Seed Metric
RIP	0, which is interpreted as infinity
IGRP/EIGRP	0, which is interpreted as infinity
OSPF	20 for all except BGP routes, which have a default seed metric of 1
IS-IS	0
BGP	BGP metric is set to IGP metric value

14.

What is the safest way to perform redistribution between two routing protocols?

Answer:

The safest way to perform redistribution is to redistribute routes in only one direction, on only one boundary router within the network.

15.

Can redistribution be configured between IPX RIP and IP RIP? Between IPX EIGRP and IP EIGRP? Between IP EIGRP and OSPF?

Answer:

You can redistribute only protocols that support the same protocol stack. Therefore, redistribution cannot be configured between IPX RIP and IP RIP or between IPX EIGRP and IP EIGRP. Redistribution can be configured between IP EIGRP and OSPF.

16.

When configuring redistribution into RIP, what is the metric-value parameter?

Answer:

The metric-value parameter in the redistribute command for RIP is an optional parameter used to specify the RIP seed metric for the redistributed route. The default seed metric for RIP is 0, which is interpreted as infinity. The metric for RIP is hop count.

17.

Router A is running RIPv2 and OSPF. In the RIPv2 domain, it learns about the 10.1.0.0/16 and 10.3.0.0/16 routes. In the OSPF domain, it learns about the 10.5.0.0/16 and 172.16.1.0/24 routes. What is the result of the following configuration on Router A?

              router ospf 1
                redistribute rip metric 20

Answer:

The subnets keyword is not configured on this redistribute command. As a result, the 10.1.0.0/16 and 10.3.0.0/16 routes are not redistributed into the OSPF domain.

18.

What are the five components of the EIGRP routing metric?

Answer:

Bandwidth—The route’s minimum bandwidth in kbps

Delay—Route delay in tens of microseconds

Reliability—The likelihood of successful packet transmission expressed as a number from 0 to 255, where 255 means that the route is 100 percent reliable

Loading—The route’s effective loading, expressed as a number from 1 to 255, where 255 means that the route is 100 percent loaded

MTU—Maximum transmission unit, the maximum packet size along the route in bytes. An integer greater than or equal to 1

19.

When redistributing routes into IS-IS, what is the default level-value parameter?

Answer:

The default for level-value is level-2.

20.

What happens if you use the metric parameter in a redistribute command and you use the default-metric command?

Answer:

If you use the metric parameter in a redistribute command, you can set a different default metric for each protocol being redistributed. A metric configured in a redistribute command overrides the value in the default-metric command for that one protocol.

21.

What does the passive-interface default command do?

Answer:

The passive-interface command prevents routing updates for a routing protocol from being sent through a router interface. The passive-interface default command sets all router interfaces to passive.

22.

Suppose you have a dialup WAN connection between site A and site B. What can you do to prevent excess routing update traffic from crossing the link but still have the boundary routers know the networks that are at the remote sites?

Answer:

Use static routes, possibly in combination with passive interfaces.

23.

A distribute list allows routing updates to be filtered based on what?

Answer:

Options in the distribute-list command allow updates to be filtered based on factors including the following:

Incoming interface
Outgoing interface
Redistribution from another routing protocol

24.

What is the difference between the distribute-list out and distribute-list in commands?

Answer:

The distribute-list out command filters updates going out of the interface or routing protocol specified in the command, into the routing process under which it is configured.

The distribute-list in command filters updates going into the interface specified in the command, into the routing process under which it is configured.

25.

What command is used to configure filtering of the routing update traffic from an interface? At what prompt is this command entered?

Answer:

To assign an access list to filter outgoing routing updates, use the distribute-list {access-list-number | name} out [interface-name | routing-process [routing-process parameter]] command. This command is entered at the Router(config-router)# prompt.

26.

True or false: In a route map statement with multiple match commands, all match statements in the route map statement must be considered true for the route map statement to be considered matched.

Answer:

True

27.

True or false: In a match statement with multiple conditions, all conditions in the match statement must be true for that match statement to be considered a match.

Answer:

False. In a single match statement that contains multiple conditions, at least one condition in the match statement must be true for that match statement to be considered a match.

28.

What are some applications of route maps?

Answer:

Route filtering during redistribution

PBR

NAT

BGP

29.

What is the map-tag parameter in a route-map command?

Answer:

map-tag is the name of the route map.

30.

What commands would be used to configure the use of a route map called TESTING when redistributing OSPF 10 traffic into RIP?

Answer:

router rip
  redistribute ospf 10 route-map TESTING

31.

What does the following command do?

distance 150 0.0.0.0 255.255.255.255 3

Answer:

The distance command is used to change the default administrative distance of routes from specific source addresses that are permitted by an access list. The parameters in this command are as follows:

Parameter	Description
150	Defines the administrative distance that specified routes are assigned
0.0.0.0 255.255.255.255	Defines the source address of the router supplying the routing information—in this case, any router
3	Defines the access list to be used to filter incoming routing updates to determine which will have their administrative distance changed

Thus, routes matching access list 3 from any router are assigned an administrative distance of 150.

32.

What command can be used to discover the path that a packet takes through a network?

Answer:

The traceroute privileged EXEC command.

33.

What are the three DHCP roles that a Cisco IOS device can perform?

Answer:

Cisco IOS devices can be DHCP servers, DHCP relay agents, and DHCP clients.

34.

In what ways can DHCP addresses be allocated?

Answer:

DHCP supports three possible address allocation mechanisms:

Manual—The network administrator assigns an IP address to a specific MAC address. DHCP is used to dispatch the assigned address to the host.
Automatic—The IP address is permanently assigned to a host.
Dynamic—The IP address is assigned to a host for a limited time or until the host explicitly releases the address. This mechanism supports automatic address reuse when the host to which the address has been assigned no longer needs the address.

35.

What does the service dhcp command do?

Answer:

The Router(config)#service dhcp command enables DHCP features on router; it is on by default.

36.

What must be enabled on an interface for the IOS DHCP relay agent to be enabled?

Answer:

The Cisco IOS DHCP server and relay agent are enabled by default. However, the Cisco IOS DHCP relay agent will be enabled on an interface only when a helper address is configured to enable the DHCP broadcast to be forwarded to the configured DHCP server.

37.

Packets sent to which ports are forwarded by default when the ip helper-address command is configured on an interface?

Answer:

By default, the ip helper-address command enables forwarding of packets sent to all the well-known UDP ports that may be included in a UDP broadcast message, which are the following:

Time: 37
TACACS: 49
DNS: 53
BOOTP/DHCP server: 67
BOOTP/DHCP client: 68
TFTP: 69
NetBIOS name service: 137
NetBIOS datagram service: 138

Chapter 8

What is the difference between an IGP and an EGP?

Answer:

An IGP is a routing protocol used to exchange routing information within an AS. An EGP is a routing protocol used to connect between autonomous systems.

What type of routing protocol is BGP?

Answer:

BGP is an exterior path vector routing protocol.

What is BGP multihoming?

Answer:

Multihoming describes when an AS is connected to more than one ISP. This is usually done for one of the following reasons:

To increase the reliability of the Internet connection so that if one connection fails, another is still available
To increase performance so that better paths to certain destinations can be used

What are three common design options for BGP multihoming?

Answer:

All ISPs pass only default routes to the AS.

All ISPs pass default routes and provider-owned specific routes to the AS.

All ISPs pass all routes to the AS.

What are some advantages of getting default routes and selected specific routes from your ISPs?

Answer:

Acquiring a partial BGP table from each ISP is beneficial because path selection will be more predictable than when using a default route. For example, the ISP that a specific router within the AS uses to reach the networks that are passed into the AS will be based on the BGP path attributes; it usually is the shortest AS-path. If instead only default routes are passed into the AS, the ISP that a specific router within the AS uses to reach any external address is decided by the IGP metric used to reach the default route within the AS.

What is a disadvantage of having all ISPs pass all BGP routes into your AS?

Answer:

This configuration requires a lot of resources within the AS, because it must process all the external routes.

A BGP router knows of three paths to a network and has chosen the best path. Can this BGP router advertise to its peer routers a route to that network other than the best path?

Answer:

No. BGP specifies that a BGP router can advertise to its peers in neighboring autonomous systems only those routes that it itself uses—in other words, its best path.

When is it appropriate to use BGP to connect to other autonomous systems?

Answer:

BGP use in an AS is most appropriate when the effects of BGP are well-understood and at least one of the following conditions exists:

The AS allows packets to transit through it to reach other autonomous systems (for example, it is a service provider).
The AS has multiple connections to other autonomous systems.
Routing policy and route selection for traffic entering and leaving the AS must be manipulated.

When is it appropriate to use static routes rather than BGP to interconnect autonomous systems?

Answer:

It is appropriate to use static routes rather than BGP if at least one of the following conditions exists:

A single connection to the Internet or another AS
Lack of memory or processor power on routers to handle constant BGP updates
You have limited understanding of route filtering and the BGP path-selection process

10.

What protocol does BGP use as its transport protocol? What port number does BGP use?

Answer:

BGP uses TCP as its transport protocol; port 179 has been assigned to BGP.

11.

How does BGP guarantee a loop-free AS path?

Answer:

The BGP AS path is guaranteed to always be loop-free, because a router running BGP does not accept a routing update that already includes its AS number in the path list. Because the update has already passed through its AS, accepting it again would result in a routing loop.

12.

Any two routers that have formed a BGP connection can be referred to by what two terms?

Answer:

Any two routers that have formed a BGP connection are called BGP peer routers or BGP neighbors.

13.

Write a brief definition for each of the following:

IBGP
EBGP
Well-known attribute
Transitive attribute
BGP synchronization

Answer:

IBGP—When BGP is running between routers within one AS, it is called IBGP.

EBGP—When BGP is running between routers in different autonomous systems, it is called EBGP.

Well-known attribute—A well-known attribute is one that all BGP implementations must recognize. Well-known attributes are propagated to BGP neighbors.

Transitive attribute—A transitive attribute that is not implemented in a router can be passed to other BGP routers untouched.

BGP synchronization—The BGP synchronization rule states that a BGP router should not use or advertise to an external neighbor a route learned by IBGP unless that route is local or is learned from an IGP. BGP synchronization is disabled by default in Cisco IOS Software Release 12.2(8)T and later; it was on by default in earlier Cisco IOS Software releases.

14.

What tables are used by BGP?

Answer:

A router running BGP keeps its own table for storing BGP information received from and sent to other routers. This table is separate from the IP routing table in the router. The router can be configured to share information between the BGP table and the IP routing table. BGP also keeps a neighbor table containing a list of neighbors that it has a BGP connection with.

15.

What are the four BGP message types?

Answer:

The four BGP message types are open, keepalive, update, and notification.

16.

How is the BGP router ID selected?

Answer:

The BGP router ID is an IP address assigned to that router and is determined on startup. The BGP router ID is chosen the same way that the OSPF router ID is chosen—it is the highest active IP address on the router, unless a loopback interface with an IP address exists, in which case it is the highest such loopback IP address. Alternatively, the router ID can be statically configured, overriding the automatic selection.

17.

What are the BGP states a router can be in with its neighbors?

Answer:

BGP is a state machine that takes a router through the following states with its neighbors:

Idle
Connect
Active
Open sent
Open confirm
Established

Only when the connection is in the established state are update, keepalive, and notification messages exchanged.

18.

What type of BGP attributes are the following?

AS-path
Next-hop
Origin
Local preference
Atomic aggregate
Aggregator
Community
Multi-exit-discriminator

Answer:

The following are well-known mandatory attributes:

AS-path
Next-hop
Origin

The following are well-known discretionary attributes:

Local preference
Atomic aggregate

The following are optional transitive attributes:

Aggregator
Community
The multi-exit-discriminator (MED) is an optional nontransitive attribute.

19.

When IBGP advertises an external update, where does the value for the next-hop attribute of an update come from?

Answer:

When IBGP advertises an external update, the value of the next-hop attribute is carried from the EBGP update, by default.

20.

Describe the complication that an NBMA network can cause for an update’s next-hop attribute.

Answer:

When running BGP over a multiaccess network, a BGP router uses the appropriate address as the next-hop address to avoid inserting additional hops into the path. The address used is of the router on the multiaccess network that sent the advertisement. On Ethernet networks, that router is accessible to all other routers on the Ethernet. On NBMA media, however, all routers on the network might not be accessible to each other, so the next-hop address used might be unreachable. This behavior can be overridden by configuring a router to advertise itself as the next-hop address for routes sent to other routers on the NBMA network.

21.

Complete the following table to answer these questions about three BGP attributes:

In which order are the attributes preferred (1, 2, or 3)?
For the attribute, is the highest or lowest value preferred?
Which other routers, if any, is the attribute sent to?

Answer:

Attribute	Order Preferred In	Highest or Lowest Value Preferred?	Sent to Which Other Routers?
Local preference	2	Highest	Internal BGP neighbors only.
MED	3	Lowest	External BGP neighbors; those routers propagate the MED within their AS, and the routers within the AS use the MED, but do not pass it on to the next AS.
Weight	1	Highest	Not sent to any BGP neighbors; local to the router only.

22.

When is it safe to have BGP synchronization disabled?

Answer:

It is safe to have BGP synchronization disabled only if all routers in the transit path in the AS (in other words, in the path between the BGP border routers) are running BGP.

23.

What does the neighbor 10.1.1.1 ebgp-multihop command do?

Answer:

The neighbor 10.1.1.1 ebgp-multihop command sets the Time to Live (TTL) value for the EBGP connection to 10.1.1.1 to 255 (by default). This command is necessary if the EBGP neighbor address 10.1.1.1 is not directly connected to this router. An additional parameter for this command allows you to set the TTL to another value.

24.

Which commands are used to configure Routers A and B if Router A is to run BGP in AS 65000 and establish a neighbor relationship with Router B in AS 65001? The two routers are directly connected but should use their loopback 0 addresses to establish the BGP connection; Router A has loopback 0 address 10.1.1.1/24, and Router B has loopback 0 address 10.2.2.2/24.

Answer:

The BGP configuration for Router A is as follows:

     RouterA(config)#router bgp 65000
     RouterA(config-router)#neighbor 10.2.2.2 remote-as 65001
     RouterA(config-router)#neighbor 10.2.2.2 update-source loopback 0
     RouterA(config-router)#neighbor 10.2.2.2 ebgp-multihop 2

The BGP configuration for Router B is as follows:

     RouterB(config)#router bgp 65001
     RouterB(config-router)#neighbor 10.1.1.1 remote-as 65000
     RouterB(config-router)#neighbor 10.1.1.1 update-source loopback 0
     RouterB(config-router)#neighbor 10.1.1.1 ebgp-multihop 2

25.

What command disables BGP synchronization if it is enabled?

Answer:

Use the no synchronization router configuration command to disable BGP synchronization; in current IOS releases it is disabled by default.

26.

Which command would Router A in AS 65000 use to activate an IBGP session with Router B, 10.1.1.1, also in AS 65000?

Answer:

The neighbor 10.1.1.1 remote-as 65000 router configuration command would be used.

27.

What is the difference between the BGP neighbor command and the BGP network command?

Answer:

The neighbor command tells BGP where to advertise. The network command tells BGP what to advertise.

28.

What does the BGP network 192.168.1.1 mask 255.255.255.0 command do?

Answer:

If you configure network 192.168.1.1 mask 255.255.255.0, BGP looks for exactly 192.168.1.1/24 in the routing table. It might find 192.168.1.0/24 or 192.168.1.1/32, but it will never find 192.168.1.1/24. Because the routing table does not contain a specific match to the network, BGP does not announce the 192.168.1.1/24 network to any neighbors.

29.

What does the clear ip bgp 10.1.1.1 soft out command do?

Answer:

The soft out option of the clear ip bgp command allows BGP to do a soft reset for outbound updates. The router issuing the soft out command does not reset the BGP session; instead, the router creates a new update and sends the whole table to the specified neighbors. This update includes withdrawal commands for networks that the other neighbor will not see anymore based on the new outbound policy. (Note that the soft keyword of this command is optional; clear ip bgp 10.1.1.1 out does a soft reset for outbound updates.)

30.

Which command is used to display detailed information about BGP connections to neighbors?

Answer:

The show ip bgp neighbors command is used to display detailed information about BGP connections to neighbors.

31.

What does a > in the output of the show ip bgp command mean?

Answer:

The > indicates the best path for a route selected by BGP; this route is offered to the IP routing table.

32.

What column in the show ip bgp command output displays the MED?

Answer:

The metric column displays the MED.

33.

How is the established neighbor state represented in the output of the show ip bgp summary command?

Answer:

If the neighbor state is established, the State/PfxRcd column either is blank or has a number in it. The number represents how many BGP network entries have been received from this neighbor.

34.

What type of authentication does BGP support?

Answer:

BGP supports Message Digest 5 (MD5) neighbor authentication. MD5 sends a “message digest” (also called a “hash”), which is created using the key and a message. The message digest is then sent instead of the key. The key itself is not sent, preventing it from being read while it is being transmitted. This ensures that nobody can eavesdrop on the line and learn keys during transmission.

35.

How can BGP path manipulation affect the relative bandwidth used between two connections to the Internet?

Answer:

BGP path manipulation can affect which traffic uses which Internet connection. For example, all traffic going to a particular IP address or AS can be forced to go out one connection to the Internet, and all other traffic can be routed out the other connection. Depending on the volume of Internet traffic, the bandwidth of these connections is affected.

36.

Describe what the following configuration on Router A does:

       route-map local_pref permit 10
        match ip address 65
        set local-preference 300
       route-map local_pref permit 20
       router bgp 65001
        neighbor 192.168.5.3 remote-as 65002
        neighbor 192.168.5.3 route-map local_pref in

Answer:

The first line of the route map called local_pref is a permit statement with a sequence number of 10; this defines the first route-map statement. The match condition for this statement checks all networks to see which are permitted by access list 65. The route map sets these networks to a local preference of 300.

The second statement in the route map called local_pref is a permit statement with a sequence number of 20, but it does not have any match or set statements. Because there are no match conditions for the remaining networks, they are all permitted with their current settings. In this case, the local preference for the remaining networks stays set at the default of 100. This route map is linked to neighbor 192.168.5.3 as an inbound route map. Therefore, as Router A receives updates from 192.168.5.3, it processes them through the local_pref route map and sets the local preference accordingly as the networks are placed into Router A’s BGP forwarding table.

37.

Place the BGP route selection criteria in order from the first step to the last step evaluated by placing a number in the blank provided.

Answer:

10	Prefer the path with the lowest neighbor BGP router ID
6	Prefer the lowest MED
4	Prefer the shortest AS-path
9	Prefer the oldest route for EBGP paths
5	Prefer the lowest origin code
1	Prefer the highest weight
8	Prefer the path through the closest IGP neighbor
2	Prefer the highest local preference
3	Prefer the route originated by the local router
11	Prefer the route with the lowest neighbor IP address
7	Prefer the EBGP path over the IBGP path

38.

What command is used to assign a weight to updates from a BGP neighbor connection?

Answer:

The neighbor {ip-address | peer-group-name} weight weight router configuration command is used to assign a weight to updates from a neighbor connection.

Chapter 9

Why is IP multicast considered more efficient than unicast?

Answer:

Multicast data is sent from the source as one stream; this single data stream travels as far as it can in the network. Devices only replicate the data if they need to send it out on multiple interfaces to reach all members of the destination multicast group.

What are some disadvantages of using UDP-based multicast applications?

Answer:

Some disadvantages are as follows:

UDP’s best-effort delivery results in occasional packet drops.
UDP’s lack of congestion control may result in network congestion and overall network degradation.
Duplicate packets may occasionally be generated as multicast network topologies change.
Out-of-sequence delivery of packets to the application may result during network topology changes or other network events.

What is the range of multicast IP addresses?

Answer:

The Class D multicast address range is 224.0.0.0 through 239.255.255.255.

Match the range of IP multicast addresses with its description:

Range of Addresses	Description
1—224.0.0.0 through 224.0.0.255	A—Globally scoped addresses
2—224.0.1.0 through 238.255.255.255	B—Organization local scope addresses
3—239.0.0.0 through 239.255.255.255	C—Local scope addresses
4—239.255.0.0/16 (and 239.252.0.0/16, 239.253.0.0/16, and 239.254.0.0/16)	D—Site-local scope addresses
5—239.192.0.0 to 239.251.255.255	E—Limited, or administratively, scoped addresses

Answer:

1—C
2—A
3—E
4—D
5—B

In an Ethernet address, which bit indicates that the frame is a multicast frame?

Answer:

In the 802.3 standard, bit 0 of the first octet is used to indicate a broadcast or multicast frame.

How are IP multicast addresses translated to Layer 2 MAC multicast addresses?

Answer:

The translation between IP multicast and layer 2 multicast MAC address is achieved by the mapping of the low-order 23 bits of the IP (Layer 3) multicast address into the low-order 23 bits of the MAC (Layer 2) address.

How many IP multicast addresses map to a Layer 2 MAC multicast address?

Answer:

Because there are 28 bits of unique address space for an IP multicast address (32 minus the first 4 bits containing the 1110 Class D prefix), and there are only 23 bits mapped into the MAC address, there are five (28 – 23 = 5) bits of overlap. These 5 bits represent 2⁵ = 32 addresses. Thus, there is a 32:1 overlap of IP addresses to MAC addresses, so 32 IP multicast addresses map to the same MAC multicast address.

Which two types of devices is IGMP used between? Which two types of devices is CGMP used between?

Answer:

IGMP is used between a host and its local router. CGMP is used between routers and switches.

Describe the difference between how a host leaves a group when it is running IGMPv1 versus when it is running IGMPv2.

Answer:

IGMPv1 does not have a mechanism defined for hosts to leave a multicast group. IGMPv1 hosts therefore leave a group silently at any time, without any notification to the router. An IGMPv2 Leave Group message allows hosts to tell the router they are leaving the group.

10.

To which address does a host send a multicast report in IGMPv2? In IGMPv3?

Answer:

In IGMPv2, reports are sent to 224.0.0.2 (all multicast routers). In IGMPv3, reports are sent to 224.0.0.22 rather than 224.0.0.2.

11.

What is IGMP snooping?

Answer:

With IGMP snooping, a switch eavesdrops on the IGMP messages sent between routers and hosts, and updates its MAC address table accordingly. The switch must be IGMP aware to listen in on the IGMP conversations between hosts and routers.

12.

Which statement best describes the interaction between the PIM protocol and a unicast routing protocol running on a network?

There is no interaction between the two protocols.
Only PIM or a unicast routing protocol can be run in a network; they cannot be run simultaneously.
PIM uses the routing table populated by the unicast routing protocol in its multicast routing calculations.
The unicast routing protocol uses the routing table populated by PIM in its multicast routing calculations.

Answer:

13.

Select the two true statements.

A shared tree is created for each source sending to each multicast group.
A source tree is created for each source sending to each multicast group.
A shared tree has a single common root, called an RP.
A source tree has a single common root, called an RP.

Answer:

b, c

14.

Which type of distribution tree does PIM-SM use?

Answer:

PIM-SM uses a shared tree and therefore requires an RP to be defined.

15.

What does the notation (S, G) indicate?

Answer:

The notation (S, G) (pronounced “S comma G”) is the forwarding state associated with a source tree, where S is the IP address of the source and G is the multicast group address.

16.

What does the notation (*, G) indicate?

Answer:

The notation (*, G) (pronounced “star comma G”) is the default forwarding state for a shared tree, where * is a wildcard entry, meaning any source, and G is the multicast group address.

17.

What is the recommended PIM mode on Cisco routers?

Answer:

Cisco recommends PIM sparse-dense mode for IP multicast, because PIM-DM does not scale well and requires a lot of router resources, and PIM-SM has limited RP configuration options.

18.

Which command enables IP multicasting on a Cisco router?

Answer:

The ip multicast-routing global configuration command enables IP multicast on a Cisco router.

19.

What are the multicast addresses 224.0.1.39 and 224.0.1.40 used for?

Answer:

An RP router sends an auto-RP message to 224.0.1.39, announcing itself as a candidate RP. An RP-mapping agent router listens to the 224.0.1.39 address and sends a RP-to-group mapping message to 224.0.1.40. Other PIM routers listen to 224.0.1.40 to automatically discover the RP.

20.

Which command is used to display the IP multicast routing table on a Cisco router?

Answer:

The show ip mroute [group-address] [summary] [count] [active kbps] command displays the IP multicast routing table.

21.

Which command is used on a Cisco router to display information about multicast routers that are peering with the local router?

Answer:

The mrinfo [hostname | address] command displays information about multicast routers that are peering with the local router (if no address is specified) or with the specified router.

22.

What does the show ip igmp groups command display?

Answer:

The show ip igmp groups [group-address | type number] command lists the multicast groups known to the router—both local groups (directly connected) and those that were learned via IGMP.

Chapter 10

What are some of the features of IPv6?

Answer:

IPv6 features include a larger address space, a simplified header, support for mobility and security, and a richness of transition solutions.

How many bits are in an IPv6 address?

Answer:

There are 128 bits in an IPv6 address.

How long is the basic IPv6 packet header?

Answer:

The IPv6 packet header is 40 octets.

What is the flow label in the IPv6 packet header used for?

Answer:

The 20-bit flow label field is new in IPv6. It can be used by the source of the packet to tag the packet as being part of a specific flow, allowing multilayer switches and routers to handle traffic on a per-flow basis rather than per-packet, for faster packet-switching performance. This field can also be used to provide QoS.

Does the IPv6 packet header have a checksum field?

Answer:

The IPv6 header does not have a header checksum field. Because link-layer technologies perform checksum and error control and are considered relatively reliable, an IP header checksum is considered to be redundant. Without the IP header checksum, upper-layer checksums, such as within UDP, are now mandatory.

In general which node processes IPv6 extension headers?

Answer:

Generally, extension headers are not examined or processed by any node other than the node to which the packet is destined. The destination node examines the first extension header (if there is one); the contents of an extension header determine whether or not the node should examine the next header. Therefore, extension headers must be processed in the order they appear in the packet.

In what format are IPv6 addresses written?

Answer:

IPv6 addresses are written as hexadecimal numbers with colons between each set of four hexadecimal digits (which is 16 bits). The format is x:x:x:x:x:x:x:x, where x is a 16-bit hexadecimal field.

Which of the following are valid representations of the IPv6 address 2035:0001:2BC5:0000:0000:087C:0000:000A?

2035:0001:2BC5::087C::000A
2035:1:2BC5::87C:0:A
2035:0001:2BC5::087C:0000:000A
2035:1:2BC5:0:0:87C::A
2035:1:2BC5::087C:A

Answer:

b, c, d

What is the format of an IPv6 broadcast address?

Answer:

IPv6 does not have broadcast addresses.

10.

Which of the following are the true statements?

A packet that is sent to an IPv6 anycast address goes to the closest interface identified by that address.
A packet that is sent to an IPv6 anycast address goes to all interfaces identified by that address.
A packet that is sent to an IPv6 multicast address goes to the closest interface identified by that address.
A packet that is sent to an IPv6 multicast address goes to all interfaces identified by that address.

Answer:

a, d

11.

How is an IPv6 interface identifier created for Ethernet interfaces?

Answer:

The interface identifier used for Ethernet is based on the MAC address of the interface and is in an extended universal identifier 64-bit (EUI-64) format. The EUI-64 format interface ID is derived from the 48-bit link-layer MAC address by inserting the hexadecimal number FFFE between the upper 3 bytes (the organizationally unique identifier [OUI] field) and the lower 3 bytes (the vendor code or serial number) of the link-layer address. The seventh bit in the high-order byte is set to 1 (equivalent to the IEEE G/L bit) to indicate the uniqueness of the 48-bit address.

12.

What is the IPv6 unicast address space?

Answer:

The IPv6 unicast address space encompasses the entire IPv6 address range, with the exception of the FF00::/8 range (addresses starting with binary 1111 1111), which is used for multicast addresses.

13.

What is the IPv6 link-local prefix?

Answer:

The IPv6 link-local prefix is FE80::/10.

14.

What is the IPv6 multicast prefix?

Answer:

The IPv6 multicast addresses are defined by the prefix FF00::/8.

15.

What is an IPv6 solicited-node multicast address used for?

Answer:

Solicited-node multicast addresses on a link have addresses FF02::1:FFXX:XXXX, where the XX:XXXX is the rightmost 24 bits of the corresponding unicast or anycast address of the node. Neighbor solicitation messages are sent on a local link when a node wants to determine the link-layer address of another node on the same local link, similar to ARP in IPv4.

16.

How does IPv6’s stateless autoconfiguration work?

Answer:

An IPv6 router on a local link can send (either periodically or upon a host’s request) network information, such as the 64-bit prefix of the local link network and the default route, to all the nodes on the local link. Hosts can autoconfigure themselves by appending their IPv6 interface identifier (in EUI-64 format) to the local link prefix (64 bits).

17.

How does IPv6 mobility work?

Answer:

Each IPv6 mobile node is always identified by its home address, regardless of where it is. When it is away from its home, a mobile node is also associated with a care-of address, which provides information about the mobile node’s current location. IPv6 packets addressed to a mobile node’s home address are transparently routed to its care-of address. All IPv6 nodes, whether mobile or stationary, can communicate with mobile nodes.

18.

What are some of the similarities between OSPFv2 and OSPFv3?

Answer:

The similarities between OSPFv3 and OSPFv2 include the following:

OSPFv3 uses the same basic packet types as OSPFv2: hello, DBD (also called DDP), LSR, LSU, and LSAck. Some of the fields within the packets have changed.
The mechanisms for neighbor discovery and adjacency formation are identical.
OSPFv3 operations over NBMA topologies are the same. The RFC-compliant nonbroadcast and point-to-multipoint modes are supported. OSPFv3 also supports the other modes from Cisco such as point-to-point and broadcast.
LSA flooding and aging are the same.

19.

Fill in the following table to indicate the OSPFv3 packet types.

Answer:

Packet Type	Description
1	Hello
2	DBD
3	LSR
4	LSU
5	LSAck

20.

Which IPv6 multicast addresses does OSPFv3 use?

Answer:

The multicast addresses used by OSPFv3 are as follows:

FF02::5—. This address represents all SPF routers on the link-local scope; it is equivalent to 224.0.0.5 in OSPFv2.
FF02::6—. This address represents all DRs on the link-local scope; it is equivalent to 224.0.0.6 in OSPFv2.

21.

How many bits is an OSPFv3 router ID?

Answer:

The OSPFv3 router ID remains at 32 bits.

22.

What are the two new LSAs introduced in OSPFv3?

Answer:

The two new LSAs in OSPFv3 are as follows:

Link LSAs (type 8)—Type 8 LSAs have link-local flooding scope and are never flooded beyond the link with which they are associated. Link LSAs provide the link-local address of the router to all other routers attached to the link, inform other routers attached to the link of a list of IPv6 prefixes to associate with the link, and allow the router to assert a collection of options bits to associate with the network LSA that will be originated for the link.
Intra-area prefix LSAs (type 9)—A router can originate multiple intra-area prefix LSAs for each router or transit network, each with a unique link-state ID. The link-state ID for each intra-area prefix LSA describes its association to either the router LSA or the network LSA. The link-state ID also contains prefixes for stub and transit networks.

23.

What is the OSPFv3 instance ID used for?

Answer:

An OSPF instance (also known as an OSPF process) can be considered a logical router running OSPF in a physical router. The instance ID controls selection of other routers as neighboring routers; the router becomes neighbors only with routers that have the same instance ID.

24.

Which command is used to summarize IPv6 OSPF routes?

Answer:

To consolidate and summarize routes at an area boundary use the area area-id range ipv6-prefix/prefix-length [advertise | not-advertise] [cost cost] IPv6 OSPF router configuration command.

25.

What are some of the techniques available to transition from IPv4 to IPv6?

Answer:

The two most common techniques to transition from IPv4 to IPv6 are dual stack and tunneling. Alternatively, mechanisms that allow communication between IPv4 and IPv6 nodes can be used.

26.

What addresses do the routers involved in 6-to-4 tunneling use?

Answer:

Each 6-to-4 edge router has an IPv6 address with a /48 prefix, which is the concatenation of 2002::/16 and the hexadecimal representation of the IPv4 address of the edge router; 2002::/16 is a specially assigned address range for the purpose of 6-to-4 tunneling. The edge routers automatically build the tunnel using the IPv4 addresses that are embedded in the IPv6 addresses. For example, if the IPv4 address of an edge router is 192.168.99.1, the prefix of its IPv6 address is 2002:c0a8:6301::/48, because 0xc0a86301 is the hexadecimal representation of 192.168.99.1.

..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.

Table of Contents for A. Answers to Review Questions

Create new playlist

Sign In

Sign Up

Appendix A. Answers to Review Questions

Chapter 1

Chapter 2

Chapter 3

Chapter 4

Chapter 5

Chapter 6

Chapter 7

Chapter 8

Chapter 9

Chapter 10

Table of Contents for
A. Answers to Review Questions