Accessibility Security

Security is a popular topic and a major consideration, particularly as more companies connect to the Internet and thereby increase the chance of hackers, idly wandering into the network. Weighing the needs of users to access the network, particularly when remote access is required, against the need to secure company secrets is a difficult balance that requires careful consideration at the executive level. It is important to consider security as part of the initial design because it is very...

Adding a Network to the Topology Table

Imagine the router (Router A) that hears a new network. The administrator has plugged in another Ethernet cable to service a department that has moved into the building. As soon as Router A becomes aware of the new network, it starts to send Hello packets out the new interface. No one answers because this is an access router giving connectivity to the workstations and other end devices. There are no new entries in the neighbor table because no neighbors have responded to the Hello protocol....

Administrative Distance

The administrative distance selects one path to enter into the routing table from several paths offered by multiple routing protocols. In Figure 10-6, for example, both RIP and EIGRP have paths to the network 140.100.6.0. RIP is offering a metric of 2 hops, and EIGRP is tendering a metric of 768. Without redistribution, no conversion or choice is possible because there is no similar criteria for distinguishing the two paths. Therefore, the metric is ignored, and the administrative distance is...

An Autonomous System Defined

An autonomous system is a routing domain that shares routing information. Typically, an autonomous system is the same as an organization. Within the context of internal security, every network within the organization is available, and information about the networks is transmitted via an interior routing protocol such as EIGRP, OSPF, RIP, or IGRP. Although there may be more than one interior routing protocol running within the autonomous system, the probability is that they are sharing...

Automatic Redistribution Between Routing Protocols

Table 10-17 Automatic Redistribution Between Routing Protocols Table 10-17 Automatic Redistribution Between Routing Protocols Requires manual redistribution into other routing protocols. Unless included in the network command for the routing process, requires Will automatically redistribute between IGRP and EIGRP if the autonomous system number is the same. Otherwise, processes with different IGRP autonomous system numbers, or IGRP and EIGRP processes with different autonomous system numbers,...

Benefits of the Synchronization Rule

The following list gives reasons for the synchronization rule It prevents traffic from being forwarded to unreachable destinations. It reduces unnecessary traffic. It ensures consistency within the autonomous system. On some occasions it is useful to turn off synchronization. This is rare, and, as with any default, it is unwise to turn off this option without a detailed understanding of the network. The occasions when it may be useful to turn off synchronization are as follows If all the...

BGP4 Attributes

Attributes in BGP-4 are used to determine the best path to be selected. In essence, they are the metric for BGP-4. However, they are more than a list of variables by which a route is selected. They also carry information that decisions are based on hence the name attributes. The variables describe characteristics or attributes of the path to the destination. These characteristics can be used to distinguish the paths, and this allows a choice to be made among the paths. Some of the information...

CIDR and Route Aggregation

As explained in Chapter 3, IP Addressing, there is a shortage of IP addresses in the Internet. There is also a problem with the size of the routing tables, in terms of the memory, bandwidth, and CPU that they consume when updating the routing tables. Classless interdomain routing (CIDR) is one of the main solutions implemented in recent years. This is a method of consolidating addresses into a few summary addresses. Instead of a subnet having a subnet mask to identify the network portion of the...

CIDR as a Solution

An organization requiring multiple Class C addresses is allocated consecutive Class C addresses but issues only one address for the Internet routing entry (representing the multiple addresses). This is achieved by pulling the network mask to the left. The shorter the prefix, the more generally the network is defined the longer the prefix, the more specific the identification is. Table 3-5 visually demonstrates the use of the prefix. The Internet IP addressing group ARIN, at www.arin.net,...

Ciscos Hierarchical Design

To achieve these networks requirements that have been described and to keep local traffic local, preventing network congestion Cisco suggests a network design structure that allows for growth. The key to the design is that it is hierarchical. There is a division of functionality between the layers of the hierarchy, allowing only certain traffic based on clear criteria to be forwarded through to the upper levels. A filtering operation restricts unnecessary traffic from traversing the network....

Clients Cannot Connect to Network Resources

The client server environment is one in which applications take advantage of networks. Servers provide services to many clients that access them across the network. Both data and application software may be stored centrally on a server that allows many clients to share them. If all users depend on the client server interaction, this can create excessive traffic across the network. In a client server environment, the available resources are communicated throughout the network. The dynamic nature...

Command Summaries

This section contains a list of the commands explained in this chapter. This list is not intended to teach the use of the commands, but to remind you of the options available. network network number wildcard mask area area id This command identifies the interfaces that are running OSPF and places them in the appropriate area. summary-address address mask not-advertise tag tag This command consolidates routes into a summary route before injecting them into the external world. Remember that the...

Commands to Tune BGP4Using the Local Preference and Weight Attributes

To configure the weight attribute, use the following command neighbor ip-address peer-group-name weight weight Table 9-6 explains the meaning of the preceding syntax. Table 9-6 An Explanation of the Command to Configure the Weight Attribute This identifies that the rest of the command is directed at a BGP-4 peer. This is the IP address of the neighboring router. This identifies the BGP-4 peer group, if there is one. weight weight This is proprietary to Cisco and is used in route selection. It...

Configuration for EIGRP or IGRP

To configure the default metric for IGRP or EIGRP, use the following command syntax default-metric bandwidth delay reliability loading mtu Typically, you should take the values shown on one of the outgoing interfaces of the router being configured, by issuing this exec command The significance of the metric values is shown in Table 10-5. Table 10-5 The Parameters of the default metric Command The minimum bandwidth seen on route to the destination. It is presented The delay experienced on the...

Configuring a Virtual Link

When it is not possible to connect an area to Area 0 directly, a solution is to create an IP tunnel called a virtual link. This is remarkably easy to configure. As with many things in OSPF, of course, this ease of configuration belies the complexity of the technology being used. Many things can go wrong. The most common problem is in the address of the other end of the virtual link. The command is given between ABRs, at least one of which must be in Area 0. The command, issued at both ABRs,...

Configuring OSPF in NBMA Mode

In NBMA mode, the design considerations are imperative because the selection of the DR and BDR need to have physical connectivity to all routers in the NBMA cloud. Remember that this is a nonbroadcast environment, so the DR and BDR must be configured with a static list of the other routers attached to the cloud so that they can become neighbors and create adjacencies. This is achieved with the use of the neighbor command. Other technologies have superceded the need to manually configure the...

Configuring OSPF over an NBMA Topology

The design considerations of running OSPF over an NBMA topology are outside the scope of this book, but it is important to research this area because it speaks to the configuration choices that will be made. However, one of the common choices on a partially meshed network illustrates the kind of decisions that need to be made. If the network is partially meshed, then the choice to use only point-to-point subnets can waste addresses. If a point-to-multipoint configuration is chosen, the network...

Configuring the Administrative Distance

To ensure that the optimal path is chosen, it is sometimes necessary to change the administrative distance, to make it less favorable. The command structure is protocol-dependent, in that EIGRP requires a separate command. The following command syntax is used for EIGRP distance eigrp internal-distance external-distance The distance command, as used to configure the EIGRP administrative distance, is explained in Table 10-6. Table 10-6 Configuring Administrative Distance for EIGRP Command...

Connecting to Other Autonomous Systems The Basics of BGP4

This chapter details Border Gateway Protocol 4 (BGP-4). Although BGP-4 is covered briefly in the ACRC exam, it is given far greater attention in the CCNP CCDP Routing exam. Even so, the exam barely scratches the surface of the detail available to the protocol. This chapter deals with the basic concepts and configuration commands of BGP-4 and leads into greater complexity in the next chapter. This chapter builds on the understanding of routing within large enterprise networks that was dealt with...

Connecting to the Outside World

When connecting to the outside world, some filtering and address translation may be necessary. Unless an address has been obtained from the Internet or from an ISP, it is necessary to perform address translation. The RFC that defines NAT is RFC 1631. NAT is the method of translating an address on one network into a different address for another network. It is used when a packet is traversing from one network to another and when the source address on the transmitting network is not legal or...

Controlling Routing Updates

Various methods enable you to control the routing information sent between routers. These methods include the following Passive interfaces An interface that does not participate in the routing process. In RIP and IGRP, the process listens but will not send updates. In OSPF and EIGRP, the process neither listens nor sends updates because no neighbor relationship can form. The interfaces that participate in the interior routing process are controlled by the interface configuration. During...

Controlling Routing Updates Across the Network

The topics in this chapter deal with the traffic generated by the routing updates in terms of both the network resources that they use and the information contained within them. This covers two different but related areas. The network overhead involved in routing updates has already been dealt with in other chapters, and it keeps recurring as a theme because all network traffic directly influences the network's capability to scale or grow. The issue is very complex and deals with the design of...

Controlling Routing Updates with Filtering

Despite all the mechanisms for controlling and reducing the routing updates on your network, it is sometimes necessary to wield greater and more flexible power. This comes in the form of access lists, which when applied to routing updates are referred to as distribute lists. The logic used in the distribute lists is similar to that of an access list. It is summarized in the flowchart in Figure 10-11 and the process listed in the following text. Figure 10-11 Distribute List Logic on an Incoming...

Default Redistribution Between Routing Protocols

EIGRP is a routing protocol that carries updates for multiple protocols. The key to how this works is the separate routing tables held for each protocol, using the routing protocol as the mechanism for the forwarding of updates and path selection. EIGRP supports AppleTalk's RTMP, IPX's RIP and NLSP, as well as IP. Automatic redistribution is performed between RTMP and EIGRP, and IPX RIP and EIGRP. EIGRP must be manually redistributed into NLSP. There is also automatic redistribution between...

Designing IP Networks

The topics that make up the rest of this chapter are not in the Building Scalable Cisco Networks (BSCN) course, upon which the Routing exam is partially based. Therefore, these topics might not be on the exam, but they have been included in this chapter because they place the topic of IP addressing into a wider context. These subjects should be studied not with the intention of answering questions on the exam, but rather as information that extends the subject matter. There will be no questions...

Designs That Avoid a Fully Meshed IBGP4 Network

The problem presented by a fully meshed IBGP-4 network can be solved by design. If a hub-and-spoke network were developed, this would streamline the TCP connections. This is a good thing, but it does require some additional design and configuration. The solution is the implementation of route reflectors and the network design that they support. The design can become quite complicated with multiple route reflectors that afford redundancy, which is always reassuring. Multiple levels of route...

Distance Vector Routing Protocols

Distance vector protocols send periodic updates. These updates are sent to directly connected neighbors. The update is periodic because it waits for the timer to expire before it sends an update. After receiving a neighbor's routing table, the router updates its table and sends the modified table in subsequent updates. This is the reason that distance vector routing protocols are said to be routing by rumor. The purpose of the protocol is to provide accurate, loop-free information to the...

Do I Know This Already Quiz

The purpose of the Do I Know This Already quiz is to help you decide what parts of this chapter to use. If you already intend to read the entire chapter, you do not necessarily need to answer these questions now. This 16-question quiz helps you determine how to spend your limited study time. The quiz is sectioned into four smaller four-question quizlets, which correspond to the four topics in the chapter. Figure 2-1 outlines suggestions on how to spend your time in this chapter. Use Table 2-1...

Extended IP Access Lists

Although the same rules apply for all access lists, extended access lists allow for a far greater level of control because decisions are made at higher levels of the OSI model. The following is syntax of an extended access-list command access-list access-list-number deny permit protocol source source-wildcard destination destination-wildcard ip access-group access-list-number in out The access-list-number value must be between 100 and 199 to create an extended access list. Figure 2-5 The...

Exterior Routing Protocols

Routing protocols that exchange routing information between organizations are known as exterior routing protocols. Exterior routing protocols are highly complex. The complexity arises from the need to determine policies between different organizations. Border Gateway Protocol Version 4 (BGP-4) is an example of an exterior gateway protocol. NOTE This next section deals briefly with an older distance vector routing protocol, RIP an improved distance vector routing protocol, IGRP and a link-state...

Filter Configuration

Whenever a network is configured, that configuration must be tested, and the changes must be documented. Called maintaining the baseline, this enables you to maintain a clear knowledge of the network functionality. The commands to verify the filter configuration for either IP or IPX filters are most easily accomplished through the show commands Figure 2-6 illustrates the process logic used for access lists. Figure 2-6 Processing of an IP Access List Incoming and Outgoing Packets Figure 2-6...

Finding an Alternative Path to a Remote Network

When the path to a network is lost, EIGRP goes to a lot of trouble to find an alternative path. This process is one of the major benefits of EIGRP. The method it has chosen is very reliable and very fast. Figure 7-9 and the following list describe the process. NOTE Note that the metric shown in Figure 7-9 has been simplified for the purposes of this example. Using Figure 7-9 as reference for the topology of the network, follow the sequence of events Router D marks the routes that were reached...

Finding Neighbors with the Exchange Process

When it is connected to the network and has been configured to run OSPF, the new router must learn the network from the systems that are up and running. The method shown here, however, is the same as for a stable network. This process is shown in the stages that the systems go through while exchanging information. It is possible to see what stage an interface running OSPF is in with the command show ip ospf neighbor as well as the command debug ip ospf adjacency. Care should be taken with the...

Foundation Summary

The Foundation Summary Section is a collection of quick reference information that provides a convenient review of many key concepts in this chapter. For those of you who already feel comfortable with the topics in this chapter, this summary will help you recall a few details. For those of you who just read this chapter, this review should help solidify some key facts. For any of you doing your final preparations before the exam, these tables and figures will be a convenient way to review the...

Further Study for Final Preparation

This chapter is not the only chapter that you should use when doing your final preparation for the Routing exam. Not all the subjects in the exam are covered in this chapter. Here is a brief list of the study options provided by this book, beyond the core chapters and this scenarios chapter All prechapter quiz and chapter-ending questions, with answers, are in Appendix A, Answers to Quiz Questions. These conveniently located questions can be read and reviewed quickly, with explanations. The...

Guidelines in Network Design to Avoid Routing Loops

The principles are summarized as follows Have a sound knowledge and clear documentation of the following The network topology (physical and logical) The routing protocol domains Do not overlap routing protocols. It is much easier if the different protocols can be clearly delineated into separate domains, with routers acting in a similar function to Area Border Routers in OSPF. This is often referred to as the core and edge protocols. Identify the boundary routers on which redistribution is to...

How the Routing Table Is Kept Current and Correct

The capability to send traffic from one end of the network to the other depends on how accurate and current the routing table in every router is within the network. Although all routing protocols have this written into their mission statements, the more recent routing protocols are more efficient, so their networks scale more easily. For example, RIP will send out the entire routing table every 30 seconds, while OSPF updates contain only the change and are sent only when that change occurs....

How to Best Use This Chapter

By taking the following steps, you can make better use of your study time Keep your notes and the answers for all your work with this book in one place, for easy reference. When you take a quiz, write down your answers. Studies show that retention significantly increases by writing down facts and concepts, even if you never look at the information again. Use the diagram in Figure 7-1 to guide you to the next step. If you skip to the Foundation Summary, Q& A, and scenarios sections and have...

How to Use This Book to Pass the Exam

One way to use this book is to start at the beginning and read it cover to cover. While that would certainly help you prepare, most people do not have that much time to spare, particularly if they already have mastered some of the topics in the book. However, if you want to read the entire book and answer all the CD-ROM questions, then that is a great way to prepare For the rest of you, you might want to consider different strategies for how best to use this book, depending on what training and...

Intranet Example

Configuring the static route to null0 on an internal company router would prevent connectivity to the defined network because all traffic to that destination would be forwarded to a nonexistent interface. In Figure 2-8, Workstation A would not be capable of connecting to Server C, the development server used by the Research and Development department. The result is that the Research and Development department would be capable of seeing the rest of the organization. Indeed, the rest of the world...

Key Attributes of OSPF

OSPF is designed to offer the greatest flexibility for every situation. As an open standard, it is required to offer interoperability in conjunction with this flexibility, while allowing the network to grow. These requirements make OSPF a highly complex routing protocol. To understand this complexity, it is useful to identify the main characteristics of OSPF. These key attributes of OSPF include the following Maintaining a connection-oriented relationship with other routers on the same physical...

Learning a New Route

When the 2500 receives a network LSA update from the designated router, it goes through the following logical steps 1 The router takes the first entry from the update the first network with information about the state of its link. 2 The router verifies the type of LSA is one that can be accepted by this router. 3 Having ascertained that it is a valid LSA that it can receive, the router issues a lookup to its topological database. 4 If the LSA entry is not in the topological database, it is...

Link State Routing Protocols

A link-state routing protocol is a sophisticated protocol dedicated to maintaining loop-free, accurate tables. It does not send the entire routing table via broadcasts every 30 seconds, as the original distance vector protocols (such as RIPv1) did, but it instead utilizes multicast addressing and incremental updates. Some routing protocols may be sent updates every 30 minutes (not 30 seconds) in addition to the incremental ones. Table 4-6 is a summary of IP routing protocols and the update...

Load Balancing in EIGRP

EIGRP automatically load-balances across links of equal cost. Whether the traffic is sent on a per-destination or round-robin basis depends on the internal switching within the router. It is possible to configure EIGRP to load-balance across unequal paths using the variance command. This command allows the administrator to identify by the use of the multiplier parameter the metric scope for including additional paths. The command structure is shown here variance multiplier The multiplier is a...

Maintaining the Topology Table

The topology table is updated because the router either gains or loses direct connectivity with a router or hears a change through the network communication of EIGRP. The following three reasons may cause a topology table to be recalculated The router hears a change when a new network is available because of one of the following reasons The topology table receives an update stating that there is a new remote network. The interface sees carrier sense for the network that is configured for a...

Other Solutions to Traffic Control

It is popular to tune the update timers between routers, trading currency of the information for optimization of the bandwidth. All routers running the same routing protocol expect to hear these updates with the same frequency that they send out their own. If any of the parameters defining how the routing protocol works are changed, these alterations should be applied consistently throughout the network otherwise, routers will time out and the routing tables will become unsynchronized. WARNING...

Packets from Neighbors That Build the Topology Table

After the router knows who its neighbors are, it is in a position to create a database of feasible successors. This view of the network is held in the topology table. The topology table is created from updates received from the neighboring routers. The updates are exchanged between the neighbors. Packets called replies will also update the topology table. Replies are sent in response to queries sent by the router, inquiring about suspect routes. The queries and responses used by EIGRP for the...

Principles of a Client Server Network

To design an effective network, it is essential to understand the data flow within a network. Where to place the server relative to the clients should be decided only after considering the following factors The frequency of connection to the server The duration of the connection to the server The volume of traffic sent across the link to and from the server at a specific moment of the day The daily quantified average Analyzing the traffic patterns over time to create a baseline of the network...

Private Addresses on the Internet

Private addressing (along with VLSM, IP version 6 with an address field of 128 bits, and CIDR adressing and prefix routing) is one of the solutions the Internet community began to implement when it became apparent that there was a severe limitation to the number of IP addresses available on the Internet. Private addressing was defined by RFC 1597 and was revised in RFC 1918. It was designed as an addressing method for an organization that has no intention of ever connecting to the Internet. If...

Qa

The following questions test your understanding of the topics covered in this chapter. The final questions in this section repeat the opening Do I Know This Already questions. These are repeated to enable you to test your progress. After you have answered the questions, find the answers in Appendix A. If you get an answer wrong, review the answer and ensure that you understand the reason for your mistake. If you are confused by the answer, refer to the appropriate text in the chapter to review...

Receiving Routing Information from the Internet

When connecting into something as vast as the Internet, some planning and forethought is necessary. In particular, it is essential to decide what updates are to be sent to the outside world and how routers within the autonomous system are to know about the outside world and all that it offers. There are three main approaches to the selection of routes from the Internet Accept only default routes from all providers Accept partial routes as well as default routes from all providers Accept full...

Redistribution Between the IGP and BGP4

Up until now, the discussion has been about BGP-4, its operation, and the configuration options available. However, for most, BGP-4 is the means by which information about the Internet is brought into the internal organizational routing domain. Disseminating this information throughout the autonomous system is the subject of this next section. If the organization is not an ISP, there is a fair chance that the network is running an IGP within the autonomous system. The IP routing table generated...

Redistribution Configuration Syntax

To configure redistribution between routing protocols, the following command syntax is used redistribute protocol process-id level-1 level-1-2 level-2 metric metric-value metric-type type-value match internal external 1 external 2 tag tag-value route-map map-tag weight weight subnets This command is explained in Table 10-4. Table 10-4 Command Description of Redistribution Table 10-4 Command Description of Redistribution This is the routing protocol that is providing the routes. Remember, most...

Redistribution Example

Refer to Figure 10-13 for this example, which covers route redistribution with redundant paths between different routing protocols and resolving path selection problems that result in redistributed networks. In Figure 10-13, Router A is connected to networks 140.100.1.0 and 140.100.2.0 that are advertised via RIP to routers C and B. The routing table of Router A will show the information presented in Table 10-11. Table 10-11 Router A Routing Table Information The routing table of Router A will...

Route Selection Process

As can be seen, BGP-4 has many options by which to select one route above another. If EIGRP is complicated in its selection of feasible routes, then BGP-4 is dramatic in its choice of criteria by which the selection is made. That is the key difference. It is not the maintenance of a loopfree network with a very low convergence time that is the goal for BGP-4, but rather the capability to manipulate the traffic flow through the network. That the network is loop-free is critical to the success of...

Routing and Routed

It is important to distinguish between the datagram and the routing protocol used to determine the path of the datagram. The distinction is between the routed and the routing protocol. The routed protocol is the Layer 3 protocol used to transfer data from one end device to another across the network. The routed protocol is the Layer 3 datagram that carries the application data as well as the upper-layer information. The routing protocol is the protocol used to send updates between the routers...

Routing Protocols That Support VLSM

The following routing protocols support VLSM NOTE Static routes could be said to use VLSM. They are often used to redistribute between routing protocols sharing a NIC number when one routing protocol supports VLSM and the other does not. In these instances, the static route will define one summarized route for the non-VLSM routing protocol. This technique is also used when redistributing into BGP-4. The following routing protocols do not support VLSM

Scenario 101

Reconsider the case study at the beginning of the chapter. Duddleduddle is a large hospital with several sites in the city. Although the sites connect to a centralized patient and administration database, the hospital has fought for local autonomy based on the specialization of the site and the fact that it is its own business unit. An IT group manages the central administration and oversees the other sites. The chief information officer (CIO) who ran this group and the overall network has left...

Scenario 114 Part APlanning

Your job is to deploy a new network with three sites, as shown in Figure 11-6. The OSPF network has a shortage of IP addresses. It has been decided to readdress the network using VLSM. For Part A of this scenario, perform the following tasks 1 Plan the IP addressing, using the Class B address of 131.99.0.0. Each site consists of two buildings, with seven floors. Each floor has approximately 100 devices. The company plans to install an ISDN backup link between the buildings. 2 In the expectation...

Scenario 31 Answers

1 There are serious problems with the addressing scheme in Figure 3-16. If the network had this addressing scheme, would summarization be possible Summarization is not possible, for the following reasons The buildings do not share the same high-order bits as the campus. The campuses do not share the same high-order bits as the region. Depending on the physical design, the California campus and Building 1 could be seen as duplicate addresses. 2 Design an alternative addressing scheme using VLSM...

Scenario 42 Answers

1 What routing protocol derived the route 130.130.0.0 OSPF. 2 What router interface IP address is used to reach IP network 192.67.131.0 131.119.254.244. The fourth column of the sample output specifies the address of the router that can build a route to the specified remote network. 3 When was the last time that the route 192.65.129.0 was updated 0 02 22. The fifth column of the sample output specifies the last time the route was updated, in hours minutes seconds. 4 Through which router...

Scenario 51 Answers

1 Design the addressing scheme for the site so that summarization can be implemented at a later stage. An addressing scheme for the Los Angeles site could be as shown in Figure 5-14. 2 Determine the configuration that will be implemented across the Frame Relay cloud. The Frame Relay configuration is a hub-and-spoke topology. Because Los Angeles is the central hub of the company, it is logical that it is also the network hub. The configuration in Frame Relay would therefore be a...

Scenario 62 Answers

There is inconsistency in the routing table, and the system is extremely slow. What commands would be used to identify the problem In examining the diagram and configuration, what problems can you see Router B has been configured to be the designated router for the LAN, which means that it is dealing with all the traffic on the LAN associated with the management of OSPF. Given that the system is a 2500, it is a poor choice for a designated router. A better...

Scenario 72 Answers

1 How much bandwidth has each circuit been allocated Why was this value chosen by the administrator Because a maximum of 256 kbps is available, you cannot allow any individual PVC to handle more than 25 kbps (256 10). Note that EIGRP will not use more than 22.5 kbps (90 percent of 25 kbps) on this interface, even though its capacity is 56 kbps. This configuration will not affect user data capacity, which will still be able to use the entire 56 kbps. 2 What bandwidth utilization is available to...

Scenario

Review the output in Example 8-1, and answer the following questions. Example 8-1 Scenario 8-3 Output BGP neighbor is 155.94.83.1, remote AS 2914, external link Index 1, Offset 0, Mask 0x2 BGP version 4, remote router ID 129.250.116.16 BGP state Established, table version 457046, up for 1w5d Last read 00 00 20, hold time is 180, keepalive interval is 60 seconds Minimum time between advertisement runs is 30 seconds Received 890723 messages, 0 notifications, 0 in queue Sent 36999 messages, 0...

Scenario 93 Answers

1 Using screen 1, identify how many times the route 44.0.0.0 8 has been sent in outgoing updates from the router The prefix list tryout has 28 hits logged for the network 44.0.0.0 8. This means that 28 updates have been sent with the network 44.0.0.0 from the router to its neighbors. 2 Which path will be chosen in screen 2 to get to 33.48.124.0, and why The path using 144.39.228.49 as the next hop will be used even though it has the longer AS_Path. The local preference is set to 200. Because...

Scenario Answers

The answers provided in this section are not necessarily the only possible answers to the questions. The questions are designed to test your knowledge and to give practical exercise in certain key areas. This section is intended to test and exercise skills and concepts detailed in the body of this chapter. If your answer is different, ask yourself whether it follows the tenants explained in the answers provided. Your answer is correct not if it matches the solution...

The Distance Vector Routing Metrics

The metric used by distance vector protocols is often stated as being distance measured in the number of hand-off points or hops (routers) encountered on the way to the end device. Cisco defines IGRP and EIGRP as distance vector routing protocols. This muddies the original definition because IGRP and EIGRP use a composite and complex metric. The path selection is made using the Bellman Ford algorithm based on the metric or value of each available path. RFC 1058 discusses this in depth in...

The Implementation of IP Access Lists

Access lists can be used to either restrict or police traffic entering or leaving a specified interface. They are also used to implement what if logic on a Cisco router. This gives you the only real mechanism of programming the Cisco router. The access lists used for IP in this way enable you to apply great subtlety in the router's configuration. This chapter reviews how to configure access lists and discusses their use in an IP network. The Interconnecting Cisco Network Devices coursebook and...

The Key Features of BGP4

Discretionary (required by all routers and recognized by all routers) It is not required that these attributes be present in the update messages, but if they are present, all routers running BGP-4 will recognize and act on the information contained. These attributes are required and are therefore recognized by all BGP-4 implementations. Table 8-5 The Four Categories of Attributes (Continued) Optional The router may not recognize these attributes, but if this is the Transitive case, it marks the...

The match Commands for Policy Routing with Route Maps

The following match commands are used to determine whether the packet is one that is to be policy-routed, as opposed to being sent on its merry way. If so, it is sent down a different path, The match command is as follows match actions The match commands used in policy routing are summarized in Table 10-14. match Commands Used in Policy Routing match ip address access-list-number I name access-list-number I name This states the number or name of a standard or extended access list that will be...

The Meaning of Link State

As with a distance vector router, information is exchanged only with its directly connected neighbor. Unlike distance vector protocols, the information concerns only the local links (not the routes) connected to the router, and these links are propagated, unchanged, to every other router in the network. Therefore, every router has the same image of the network, created from the original updates from every other router in the network. The purpose of link-state routers is to reduce the network...

The Metric Field

The metric is a value that is assigned to each path based on the criteria specified in the routing protocol. The Metric field is used to determine which path to use if there are multiple paths to the remote network. The metric used depends on the routing protocol. This value is used to choose between different paths to the same destination network, to select the best path. If the values are the same, either the router selects the path that it heard first, or it uses both paths, sending the...

The Rules by Which Route Reflectors Propagate Updates

The following are the rules by which route reflectors propagate updates If a route reflector receives multiple paths to the same destination, it chooses the best path. Routes received from a client are reflected to clients and nonclients by the route reflector. This excludes the originator of the route. Routes received from a nonclient are reflected to clients only by the route reflector. Routes received from EBGP-4 are reflected to clients and nonclients by the route reflector. The command for...

The show ip eigrp neighbors Command

This command shows the neighbor table. The syntax is as follows show ip eigrp neighbors type number Example 7-2 shows the output of this command. Example 7-2 show ip eigrp neighbors Output IP-EIGRP Neighbors for process 100 Address interface Holdtime 140.100.48.22 Ethernetl 13 140.100.32.22 Ethernet0 14 140.100.32.31 Ethernet0 12 Table 7-5 explains the meaning of the important fields in Example 7-2. Table 7-5 Explanation of the show ip eigrp neighbors Command Results Table 7-5 explains the...

The show ip eigrp topology Command

This command shows the topology table. It allows for the analysis of DUAL. It will show whether the successor or the route is in an active or passive state. The syntax is as follows show ip eigrp topology autonomous-system-number ip-address mask Example 7-3 shows the output of this command. Example 7-3 show ip eigrp topology Output IP-EIGRP Topology Table for process 100 Codes P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - Reply status P 140.100.56.0 255.255.255.0, 2 successors,...

The show ip ospf borderrouters Command

This command shows the OSPF ABRs and ASBRs for which the internal router has entries in its routing table. This command is excellent for troubleshooting configuration errors and understanding how the network is communicating about its routes. Example 6-9 shows the output of this command. Example 6-9 show ip ospf border-routers Output OSPF Process 100 internal Routing Table Example 6-9 shows the output of this command. Example 6-9 show ip ospf border-routers Output OSPF Process 100 internal...

The show ip ospf Command

Example 5-6 shows the output of this command. Table 5-8 explains how to read this information. SanJose show ip ospf Routing Process ospf 100 with ID 140.100.32.10 Supports only single TOS(TOS0) routes SPF schedule delay 5 secs, Hold time between two SPFs 10 secs Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs Number of external LSA 0. Checksum Sum 0x0 Number of DCbitless external LSA 0 Number of DoNotAge external LSA 0 Number of areas in this router is 1. 1 normal 0 stub 0 nssa Area 3...

The show ip ospf database Command

This command displays the contents of the router's topological database and the different LSAs that have populated the database. In this example, because the router used is an internal router, the LSAs displayed will be the router and network updates. This command has many parameters that enable the user to examine very specific information. This section considers the general command. Example 5-7 shows the output of this command. Table 5-9 explains the meaning of the important fields. Number of...

The show ip ospf neighbor Command

Show ip ospf neighbor type number neighbor-id detail This command is used to show OSPF neighbors. All the neighbors known to the router may be viewed, or the command can be made more granular and the neighbors can be shown on a perinterface basis. One neighbor also may be picked out for scrutiny. This level of detail is excellent for troubleshooting configuration errors. Example 5-9 shows the output of this command. Table 5-11 explains how to read this information. Example 5-9 show ip ospf...

The show ip ospf virtuallinks Command

This command shows the configured virtual links that are in existence. show ip ospf virtual-links Another command to use in conjunction with this is show ip ospf neighbors. Example 6-10 shows the output of the show ip ospf virtual-links command. Example 6-10 show ip ospf virtual-links Output Virtual Link to router 140.100.32.10 is up Transit area 0.0.0.1, via interface Ethernet0, Cost of using 10 Transmit Delay is 1 sec, State DROTHER Timer intervals configured, Hello 10, Dead 40, Wait 40,...

The show ip protocols Command

This command is used to show the configuration IP routing protocols on the router. It details how the protocols were configured and how they interact with one another. It also indicates when the next updates will occur. This command is excellent for troubleshooting configuration errors and understanding how the network is communicating about its routes. Example 5-12 shows the output of this command. Table 5-12 explains how to read this information. Example 5-12 The show ip protocols Command...

The show ip route Command

This command is used to show the IP routing table on the router. It details the network as known to the router and its sources for the information (such as the routing protocols). This command is excellent for troubleshooting configuration errors and understanding how the network is communicating about its routes. To see a particular network in the routing table, issue this command Router show ip route network number Example 4-1 shows the output of this command. Table 4-5 explains how to read...

Tunneling into IP

Tunneling one protocol into another is the process by which a protocol at a specific layer of the OSI model is wrapped into another protocol of the same layer or one higher in the stack. An example of this would be IPX, which is a Layer 3 protocol being wrapped inside IP, another Layer 3 protocol. Other examples include AppleTalk inside IP, and NetBIOS or source-route bridging encapsulated in IP this is an example of a Layer 2 protocol being wrapped inside a Layer 3 protocol. Figure 2-9...

Using EIGRP in Enterprise Networks

This chapter covers in detail the Enhanced Interior Gateway Routing Protocol (EIGRP). Although EIGRP has the capability of supporting IP, AppleTalk, and IPX, the Routing exam will deal with only the mechanics of the IP routing protocol. This chapter expands on the understanding of routing within large enterprise networks that is covered in the previous chapter on OSPF within a large multiarea network. This chapter is also broken into two topics. The first part of the chapter deals theoretically...

Verifying Maintaining and Troubleshooting the Redistribution Implementation

The main key to maintaining and troubleshooting the redistribution within your network is to have a clear understanding of the network topology from both a physical and a logical perspective. The traffic flows the peaks and lows in the traffic volume are also important in truly understanding the connectivity issues within the network. From this vantage point, it is possible to interpret the output presented by the various tools available. Most of the appropriate commands in tracking...

Verifying the Configuration of Attributes

It is always important to be able to check your work, particularly when that work defines an entire organization's method of connecting into the Internet. The show ip bgp command shows all the values of all the attributes and their status. Therefore, this is a good command to verify any configurations that change attributes to tune the system and effectively manage the traffic flow to and from the autonomous system. Examples 9-6 through 9-8 show sample output from the show ip bgp command....

Verifying the Eigrp Operation

The set of commands in this section is invaluable. These commands are crucial in the configuration, maintenance, and troubleshooting of a live network. As such, they are a necessary set of tools for use on a daily basis as well as on the CCIE lab exam. For the preparation of the routing exam, understanding the output of these commands is important, not just because they may constitute questions on the exam, but because they reflect your conceptual understanding of the subject. The ability to...

Verifying the Prefix List Configuration

As always, it is important to check the configuration, especially if it involves the filtering of routes or routing updates. Table 9-4 lists the various show commands available for prefix lists. To display information about a prefix list or prefix list entries, use the show ip prefix-list exec command show ip prefix-list detail-summary name network len seq seq-num longer first-match Table 9-4 Displaying Prefix Lists Command Options show ip prefix-list detail I summary Displays information about...

Whats on the Routing 20 Exam

Every one of us would like to know exactly what is on the Routing 2.0 exam, as well as the other Cisco certification exams. Well, to be honest, exactly what is on the exam is a very closely guarded secret. Only those who write the questions for Cisco and who have access to the entire question database truly know what is entirely on the exam. The Routing 2.0 exam content that is made known by Cisco to the public is general. You can find a list of Cisco exams and the general outline that...

Why Multiple Areas

An area is a logical grouping of routers that are running OSPF with identical topological databases. It is a subdivision of the greater OSPF domain. The creation of multiple areas solves the problem of a large network outgrowing its capacity to communicate the details of the network to the routing devices charged with maintaining control and connectivity throughout the network. The division of the AS into areas allows routers in each area to maintain their own topological databases. This limits...

Foundation Topics Introduction EIGRP in an Enterprise Network

EIGRP is an enhanced version of IGRP, hence the name. It uses the same distance vector technology. The changes were effected in the convergence properties and the operating efficiency of the protocol. It has some characteristics similar to those of a link-state routing protocol. Therefore, it is sometimes referred to as a hybrid routing protocol, although Cisco calls it an advanced distance vector protocol. It is an efficient, although proprietary, solution to networking large environments as...

The show ip eigrp traffic Command

The command shows the EIGRP traffic received and generated by the router. The following is the command syntax show ip eigrp traffic autonomous-system-number Example 7-4 shows the output of this command. Example 7-4 show ip eigrp traffic Output IP-EIGRP Traffic Statistics for process 100 Table 7-7 explains the meaning of the important fields in Example 7-4. Table 7-7 Explanation of the show ip eigrp traffic Command Output Table 7-7 explains the meaning of the important fields in Example 7-4....

Assigning Ip Vlsm Subnets for WAN Connections

One common approach is to allocate a subnet that has not been assigned to hosts, and to variably subnet it for use with connectivity between rather than within areas. In this case study, it is sensible to take a subnet from the bits allocated to the buildings. Because there are enough bits allocated to address eight buildings, you have twice as many subnets as required. Even with the possibility of growth, one subnet would not be missed. Because the building bits come after the bits assigned to...

Contents

Chapter 1 Cisco Certifications, the Routing Exam, and This Book's Features 3 Cisco Routing Exam Outline File Excerpts From CCO 9 Author's Note About Exam Content 12 How to Use This Book to Pass the Exam 15 I've Taken BSCN Now What 17 I've Taken the Old ACRC Course Now What 17 I've Taken the Cisco Networking Academy Courses Now What 18 I'm New to Internetworking with Cisco, and I Will Not Be Taking the BSCN Course Now What 19 I've Learned a Lot About CCNP Topics Through Experience, But I Will...

Advantages of Summarization

The advantages of summarization are as follows To reduce the size of the routing table To make communication of routing updates more efficient To reduce CPU and memory utilization To maximize the use of IP addresses To isolate topographical changes from other areas Table 3-12 outlines the IP address ranges reserved for private addressing, as specified in RFC 1918.

The show ip ospf interface Command

Show ip ospf interface type-number This command is used to show how OSPF has been configured on an interface level, as well as how it is working at the interface. This level of detail is excellent for troubleshooting configuration errors. Example 5-8 shows the output of this command. Table 5-10 explains how to read this information. Example 5-8 show ip ospf interface type-number Output SanJose show ip ospf interface fastethernet1 0 FastEthernet1 0 is up, line protocol is up Internet Address...

The Route Map Command Syntax

The route-map command is shown here and is followed by the route map configuration commands match and set. route-map map-tag permit deny sequence-number Table 10-13 describes the syntax options available for the route-map command. Table 10-13 The route-map Command Options map-tag This is the name of the route map. This name is used to reference the route map when using the redistribute router configuration command. permit I deny (Optional) If the match criteria are met for this route map and...

Configuring EIGRP for IPX

NOTE This section is included to place EIGRP in context. The exam will test only on topics pertaining to EIGRP using IP. Therefore, this section should be read only for interest and should not be studied in depth in preparation for the Routing exam. The configuration of IPX is very similar to IP. The difference is that IPX is a client server-based protocol that was originally designed to operate in a LAN environment. Although Novell has improved its technology over the past few years to allow...

Keys Points to Remember When Designing an IP Network

The following list of items should be addressed when preparing the IP addressing plan for your network Identifying how many hosts and subnets will be required in the future requires communication with other departments in terms of the growth of personnel as well as the budget for network growth. Without the standard-issue crystal ball, a wider view must be taken at a high level to answer these questions, with the answers coming from a range of sources, including the senior management and...