CCNP Routing Study Guide- P10 pot

Which route type must be redistributed by a routing protocol if other routers are to learn about it.. Link-state routing protocols use the Hello protocol and update neighbors of changes

4. Display the topology table for RouterB, as shown here:

RouterB#show ip eigrp topology

Codes: P - Passive, A - Active, U - Update, Q - Query,

R - Reply, r - Reply status

234 Chapter 6 IGRP and EIGRP

Review Questions

1. When does EIGRP recalculate its topology table?

A. On a synchronized schedule

B. When an administrator uses the redirect command

C. Automatically every 120 seconds

D. Only when there is a change in the network topology

2. The neighbor table uses which of the following timers? (Choose all that apply.)

Review Questions 235

5. What are benefits of using a link-state routing protocol? (Choose all that apply.)

A. It uses the Hello protocol to establish adjacencies

B. It uses several components to calculate the metric of a route

C. Updates are sent only when changes occur in the network

D. It is a better protocol than distance-vector is

6. Which route type must be redistributed by a routing protocol if other routers are to learn about it?

B. To allow route information to be filtered by an access list

C. To allow routes to be sent out the specified interface, but deny route information to enter the interface

D. To allow routes to enter the interface, but deny any route tion to exit the specified interface

informa-8. How is a feasible successor chosen when the successor fails (assuming that a redundant route exists)? (Choose all that apply.)

A. The route with the next-lowest metric is chosen

B. If a router doesn’t have a feasible successor, queries are multicast

to neighboring routers in search of a feasible successor

236 Chapter 6 IGRP and EIGRP

9. Which command should be used to ensure proper metric conversion when redistributing routes from different protocols?

A. distance distance-value

B. default-metric

C. distribute-list

D. default-information

10. How is EIGRP implemented on a router?

A. ip router eigrp autonomous-system-number

B. router ip eigrp autonomous-system-number

C. router eigrp process-id

D. router eigrp autonomous-system-number

11. Which of the following are not features of EIGRP? (Choose all that apply.)

A. Incremental updates

B. Only one route per destination

C. Support for IP, IPX, and AT

D. Hybrid distance-vector and link-state routing protocol

E. Not a scalable protocol

F. Hello protocol used to establish adjacencies

12. Which of the following problems may occur if route redistribution occurs?

A. Non-optimal route choices

B. Slow convergence

C. Routing loops

D. All of the above

A. show ip eigrp mail

B. show ip eigrp sent

C. show ip eigrp traffic

D. show ip eigrp data

E. show ip eigrp counters

16. Which of the following is not a route type recognized by IGRP?

A. Network

B. Interior

C. System

D. Exterior

238 Chapter 6 IGRP and EIGRP

17. Which of the following are used by IGRP to calculate the best path to

a destination network? (Choose all that apply.)

Answers to Written Lab 239

Answers to Written Lab

1. The three EIGRP routed protocols supported by EIGRP are IP, IPX, and AppleTalk

2. Redistribution is required when more than one EIGRP session is ning and they are identified with different ASNs Redistribution shares topology information between EIGRP sessions

8. show ip route eigrp and show ip route

9. show ip eigrp neighbors

10. show ip eigrp events

240 Chapter 6 IGRP and EIGRP

Answers to Review Questions

1. D One of the great benefits of EIGRP is that it advertises only changes, and only when there is a change in the network topology does it recalculate routes Hello packets continue to be sent in order

to verify that all the attached links are still connected and did not go down

2. A, B, C The neighbor table uses the smooth round-trip timer (SRTT), the retransmission timer (RTO), and the hold timer to track its neighboring routers The FwdDelay and MaxAge timers are both used by the Spanning Tree Protocol to keep Layer 2 switches from cre-ating data loops

3. C The link will always be in Active mode regardless of the link cost because there is no other feasible successor If the link goes down, there is no other redundant link to use

4. A This is a trick question IP is a routed protocol but TCP is not Both IPX and AppleTalk are examples of routed protocols

5. A, C Link-state routing protocols use the Hello protocol and update neighbors of changes without sending the entire routing or topology table

6. D Static routes must always be redistributed by a routing protocol and always have the smallest administrative distance

7. D Passive interfaces are used for such interfaces as BRI, where you

do not want to have routing updates sent out the interface If routing updates were sent out of a BRI interface, the interface would never dis-connect You can also configure the routing traffic to be uninteresting traffic to perform a similar function

8. A, B The feasible successor, which would be the path with the lowest metric, would be chosen Or, if the router has not learned of any secondary routes, the router will query its neighbors to see if they know of any routes

next-Answers to Review Questions 241

9. B Use the default-metric command to ensure proper metric

con-version when redistributing routes from different protocols

10. D The command router eigrp followed by the ASN is used to implement EIGRP You must then identify the attached networks using the network command

11. B, E Answer B is not a feature because redundant paths are ported, and answer E is not a feature because EIGRP is the most scal-able routing protocol

sup-12. D All of these problems may occur when using route

15. C The show ip eigrp traffic command shows the sent and received packets The other commands are not real commands that can be used on a router

16. A The network route is not recognized by IGRP An interior route is

a network directly connected to a router interface A system route is a route advertised by other IGRP neighbors within the same AS An exte-rior route is learned using IGRP from a different ASN

17. A, B, C, D All of these are used by IGRP by the distance-vector rithm to determine the best path to a destination network By default however, only bandwidth and delay are used

algo-18. B IGRP can use up to four feasible successors to load balance The default is four, and the maximum is six

242 Chapter 6 IGRP and EIGRP

19. C There may be more routes in the topology table, but the imum number of feasible successors listed in the routing table is six

max-20. B The Diffusing Update Algorithm (DUAL) is used to calculate routes in EIGRP

7

BGP’s Basic Components

THE CCNP ROUTING EXAM TOPICS COVERED IN THIS CHAPTER ARE AS FOLLOWS:

Describe how to connect to another autonomous system using

an alternative to BGP, static routes

Describe BGP operations and features

Describe and configure external and internal BGP

Compare distance-vector and link-state protocol operation

Explain how BGP peering functions

This chapter covers BGP, which stands for Border Gateway Protocol BGP will be discussed in great detail, not only in this chapter but

in the two following this one as well Here we’ll focus on BGP terminology and its basics components Chapter 8, “Configuring Basic BGP,” will focus

on how BGP works and configuring BGP Chapter 9, “Monitoring, bleshooting, and Scaling BGP,” will focus on the more advanced uses of BGP, including scaling, policy implementation, and optimization techniques.For some time now, Cisco has required an understanding of BGP as a requirement for obtaining your CCIE But in order to fulfill the CCNP requirements, you needed only a basic overview and never had to deal with BGP configurations or advanced configurations There is no way that we can project to you the actual complexities of configuring BGP for an ISP needing

Trou-20 or more paths going through ISPs This is not an uncommon scenario, and we will prepare you to configure and support BGP in a real Internet environment

BGP is one of the most complex routing protocols I have ever seen It is used to connect multiple autonomous systems, which we’ll discuss in detail

In this chapter, we’ll focus on the following:

 Autonomous systems, including stud autonomous systems and transit autonomous systems

Autonomous Systems 245

 BGP update messagesBGP has been used for quite some time on routers connecting to the Inter-net The Internet can be really thought of as the backbone of thousands of small and large companies This book focuses on the latest version of BGP:

BGP version 4(BGPv4) BGPv4 is an exterior routing protocol Interior

rout-ing protocols such as RIP, IGRP, and OSPF run inside a company’s network BGP is the glue that connects the different networks to the Internet BGP also helps in finding and distributing route information

Are you ready for all of this? Let’s get started and see what an mous system is

autono-Autonomous Systems

You can imagine the Internet as a Lego castle In order to build a Lego™ castle, you need many pieces The same goes for the Internet The Internet is built with many autonomous systems, which we will think of as Lego pieces These pieces are then assembled to form a much larger piece Autonomous systems (AS) are the basic building blocks of network-to-network routing An autonomous system can be the entire corporate net-work comprised of multiple locations connecting to the network

An AS uses BGP to advertise routes in its network that need to be visible outside of the network; it also uses BGP to learn about the reachability and routes by listening to advertisement announcements from other autonomous systems Each AS can have a specific policy regarding the routes it wishes to advertise externally These policies can be different for every point in which the AS attaches to the outside world

The Internet consists of a number of commercial networks that connect to each other via tier-one providers, such as Sprint, Qwest, WorldCom/MCI, UUNet, and many others Each enterprise network or ISP must be identified

by an autonomous system number (ASN) This number allows a hierarchy to

be maintained when sharing route information

246 Chapter 7 BGP’s Basic Components

RFC 1930 defines an autonomous system as a set of routers under one or more administrations that presents a common routing policy to the internet (lowercase i) By definition, an internet is a set of interconnected networks that cooperate with each other, advertise policies, and contain a specified level of independence There are many organizations, such as the government, state departments, and financial institutions, with networks large enough to need BGP and to split into multiple autonomous systems.

Inside autonomous networks, interior routing protocols called interior gateway protocols (IGP) are used to discover the connectivity among a set of

IP subnets IGPs are well-known protocols such as the Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP), Open Shortest Path First (OSPF), and Enhanced Interior Gateway Routing Protocol (EIGRP) In Figure 7.1, we see an example of two corporate networks being connected by BGP

F I G U R E 7 1 Two corporate networks being connected by BGP

Company A

Autonomous System 204

Company B

Autonomous System 51,064

Autonomous System 64,042

Customers all in their own Autonomous Systems

ISP

Internet

Autonomous Systems 247

Variations of BGP terms will be used in the next two chapters These terms are internal BGP (iBGP) and external BGP (eBGP), also known as an interdomain routing protocol These are the same BGP protocol, but iBGP runs inside an

AS while eBGP runs outside an AS and connects one AS to another AS.

So what type of routing protocol is used to find the paths and connect these autonomous systems? An Exterior Gateway Protocol (EGP) That is exactly what BGP is, an External Gateway Protocol used to connect and find routes to and from autonomous systems

BGP is defined in many Requests For Comments (RFCs), which include

1771-1774, 1863, 1965-1966, 1997-1998, 2042, 2283, 2385, and 2439 BGPv4, the est version, and autonomous systems are defined in RFC 1771.

lat-Now we have to remember another routing protocol that learns the works and can keep loops from forming in the network In this book, there are three mapping protocol types to remember that help to determine paths and eliminate data loops:

net-Internal routing protocols These are protocols like OSPF, IGRP,

EIGRP, and RIP, which operate at Layer 3 of the OSI Reference Model They are used to learn the network topology on the internal network and

IP subnets to create routes that guarantee that there are no data loops in the Layer 3 network

External routing protocols These protocols are used to learn the

net-work topology of multiple autonomous systems or netnet-works and connect them with loop-free paths

Spanning Tree Protocol This protocol is used at Layer 2 inside a

seg-ment of an AS It ensures that the internal network topology is learned at Layer 2 and verifies that there is a path through the network without data loops

BGP uses reliable session management, using TCP port 179 for triggered UPDATE and KEEPALIVE messages to its neighbors to propagate and

248 Chapter 7 BGP’s Basic Components

A router can be a member of only one autonomous system and must appear to other autonomous systems to have one routing plan All the des-tinations must be reachable through that plan

There are 65,535 available autonomous system numbers that can be assigned, from 1 to 65,535 Autonomous system numbers (ASN) are 16-bit integers Of those 65,535 ASNs, the numbers 64,512 to 65,535 are reserved for private use This obviously means that there must be some authority available to assign these numbers to those who need them, right? Yes, there is.RFC 1930 provides guidelines for assigning BGP autonomous system numbers When you request a BGP ASN, you will be required to provide the following information:

 All administrative contacts in the company

 The Internet address of your routers

 A preferred autonomous system name

 A hardware profile of your routing hardware and the software being used In the case of Cisco, this would be the model and IOS version

 Expected deployment schedule when you will begin using two or more upstream providers

 All networks in your organization connected by the routers

The Internet Assigned Numbers Authority (IANA) is the organization that assigns BGP autonomous system numbers The IANA allows the Amer-ican Registry for Internet Numbers (ARIN) to assign autonomous system numbers for North America, South America, the Caribbean, and Africa Reseaux IP Eurpeennes-Network Information Center (RIPE-NIC) assigns the AS numbers for Europe, and the Asia Pacific-NIC (AP-NIC) assigns the numbers for Asia

Stub AS

A stub AS is a single-homed network with only one entry and exit point, as

shown in Figure 7.2 In this type of network, the stub network does not need

to learn Internet routes The reason? The local service provider or Internet Service Provider is the next hop, and all the traffic is sent to one exit interface

to the provider The provider then can have the responsibility for advertising its customers’ static routes This type of situation works well if there are rel-atively few static routes to manually configure and advertise If there are