Definition of Prefix RoutingCIDR

Prefix routing is just the means by which the Internet identifies the portion of the 32-bit TCP IP address that uniquely identifies the organization. In effect, this means that the Internet can allocate a group of class networks, which are represented by a single address. This allows for prefix routing and summarization within the routing tables of the Internet. Prefix masks represent a group of TCP IP network addresses using the method of address or subnet masks. This aggregation of Internet...

Working Configuration of OSPF on a Multiarea Network

Example 6-8 is a working configuration tested for verification. It includes many of the commands explained earlier in this chapter. This is so that you see an entire working configuration rather than the relevant segment for configuring a particular networking nuance. The configuration should be used in conjunction with Figure 6-13. Figure 6-13 Diagram of the Example 6-8 Network Figure 6-13 Diagram of the Example 6-8 Network Example 6-8 Configuring OSPF in a Multiarea Network Router(config)...

Working Configuration of OSPF on a Single Router

Example 5-1 is a working configuration tested for verification. It should be used in conjunction with Figure 5-11. SanJose SanJose SanJose SanJose SanJose SanJose SanJose SanJose SanJose SanJose SanJose SanJose SanJose SanJose SanJose SanJose SanJose config) router) network 140.100.0.0 0.0.255.255 area 3 router) interface FastEthernet1 0 ip address 140.100.17.129 255.255.255.240 ip ospf priority 100 full-duplex no shutdown ip address 140.100.17.193 255.255.255.240 ip address 140.100.32.10...

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...

Advantages of Prefix RoutingCIDR

CIDR offers several advantages, including the reduction of the size of the routing table. Prefix routing is used to reduce the size of Internet routing tables. As explained in the preceding example, the Internet gave away the equivalent of eight Class C networks, but just one network entry appeared in the Internet's routing table. In an environment that has more than 54,000 entries in the routing table at the time of this writing, the size of the routing table in many ISPs has peaked at 54,000...

Alternative Methods of Connecting to an ISP

If BGP-4 is unnecessary in your network, consider the other possibilities, including the following A default route into the ISP and a static route from the ISP into the organization. A routing protocol into the ISP, making the ISP part of your autonomous system. The ISP will be using redistribution within its domain, and it is advisable for the organization to use some form of security, in the form of access lists or a firewall. Typically the ISP will give you a written sheet explaining the...

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...

An Example of the Use of CIDR

It is easy to see how this works when the address and the mask are written in binary, as the router processes them. The Internet community has allocated a group of Class C addresses, although they are presented as a single network. Table 3-6 shows an example of an IP address in both decimal and binary format. Table 3-6 An IP Address and Mask Shown in Binary If it were a standard Class C address, the mask would be 255.255.255.0. By making the mask 255.255.248.0, the last three bits of the third...

Answers

Explain the purpose of the virtual link in Figure 6-16. In this example, Area 1 does not have a direct physical connection into Area 0. A virtual link must be configured between RTA and RTB. Area 2 is to be used as a transit area, and RTB is the entry point into Area 0. This way, RTA and Area 1 will have a logical connection to the backbone. Is the configuration of the OSPF network shown in Figure 6-17 a valid configuration Yes, the configuration is a valid one. Why would a company implement...

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,...

Avoiding Routing Loops When Redistributing

Routing loops occur when a routing protocol is fed its own networks for example, networks that originated within that routing process, but that the routing protocol now learns from another routing protocol through redistribution. The routing protocol may now see a network that it owns as having a more favorable path although this will send the traffic in the opposite direction, into a different routing protocol domain. The confusion that can be caused is enormous, and it is very easy to create...

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...

Case Study Addressing the Network

For a complicated example, use a Class B address and create an addressing scheme for Mental Merge. If the Internet assigns the address 140.100.0.0, how might you address the network shown in the diagram The first task is to determine the number of regions, campuses, buildings, floors, and hosts on each floor. You also need to consider any anticipated growth or change in the network. For this example, the network is comprised of the following Four regions exist, but the company has plans to...

Chapter Glossary

This glossary provides an official Cisco definition for key words and terms introduced in this chapter. I have supplied my own definition for terms that the Cisco glossary does not contain. The words listed here are identified in the text by italics. A complete glossary, including all the chapter terms and additional terms, can be found in Appendix C, Glossary. adjacent neighbors A neighbor is a router that is directly connected to another router. They must also have same mask and hello...

Checking the Configuration of OSPF on a Multiarea Network

The show commands shown here are in addition to the commands described in Chapter 5, in the section, Checking the Configuration of OSPF on a Single Router. The single router commands are also extremely useful in a multiarea configuration. They are all invaluable in both the configuration and maintenance of a live network. They are particularly useful in troubleshooting the network. The following are the additional commands that you can use in conjunction with single router commands when...

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,...

Cisco Routing Exam Outline File Excerpts From CCO

Given your experience, this outline and guide will help you with the best methods of preparation for the Cisco Career Certifications exam. The BSCN course is the recommended method of preparation for the Routing exam. The topic areas listed in this outline are general guidelines for the type of content that is likely to appear on the exam. However, please be advised that other relevant or related topic areas may also appear. The Routing (640-503) exam will contain a combination of the following...

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...

Configuration of Tunneling into IP

The following syntax shows the configuration for the tunnel interface command interface tunnel interface-number The following shows syntax for the configuration of the tunnel associated with the tunnel tunnel source interface-number ip-address tunnel destination hostname ip-address Table 2-3 explains the previous syntax. Table 2-3 Tunneling Configuration Explanation Table 2-3 explains the previous syntax. Table 2-3 Tunneling Configuration Explanation Identifies the interface number to be...

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 in Pointto Multipoint Mode

An OSPF point-to-multipoint interface is seen as one or more numbered point-to-point interfaces. The cloud is configured as one subnet. A host route will be added for each router involved in the OSPF cloud. NOTE The point-to-multipoint non-broadcast command option is a new feature related to point-to-multipoint networks with Cisco IOS Release 11.3a. You can find more information on the subject by searching at www.cisco.com with the keywords OSPF point-to-multipoint network with separate costs...

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...

Configuring the Default Metric

The default metric can be configured in several ways. The first is to include the metric in the redistribute command, as shown in the preceding command syntax and as illustrated in Example 10-1. Example 10-1 Including the Metric in the redistribute Command router eigrp 100 redistribute rip metric 10000 100 255 1 1500 network 140.100.0.0 passive interface e1 This configuration shows the following The use of the redistribute command The routing process from which the routes are being accepted The...

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...

Disadvantages of Policy Routing

Some things should be considered before arbitrarily deciding to implement policy routing A backup path should be in place in case the defined next-hop router goes down. If there is no alternative defined, policy routing will default to dynamic routing decisions. Additional CPU is required to examine every source address to effect the defined policy. Extra configuration is required. The possibility exists that other traffic will be disrupted. BGP-4's capability to choose the routing path via...

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...

Enabling The OSPF Routing Protocol

By default (unless the SETUP script is used), there is no IP routing protocol running on the Cisco router. This is not true of other protocols, however for example, if an IPX network address is configured on an interface, the IPX RIP process will be automatically started. To configure OSPF as the routing protocol, use the following command Here, process number is a number local to the router. It is possible to have more than one process running on a router, although this is an unusual and...

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...

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...

General Design Rules for Each Layer

A clear understanding of the traffic patterns within the organization who is connecting to whom and when helps to ensure the appropriate placement of client and servers, and eases the implementation of filtering at each layer. The filtering that is imposed by the router creates the network hierarchy illustrated in Figure 2-3. Without hierarchy, networks have less capacity to scale because the traffic must traverse every path to find its destination, and manageability becomes an issue. It is...

Guidelines for Writing Access Lists

You should adhere to the following guidelines when writing an access list Write out the purpose to be achieved by the access list in clear, simple language. Determine the placement of the access list in reference to a topology map of the network. Write out the access list, ensuring that the following is considered 1 The most frequent instance of traffic is placed first in the list, if possible, to reduce CPU processing. 2 Specific access is stated before group access is defined. 3 Group access...

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 Hierarchical Is Hierarchical

Cisco's design methodology is based on simplicity and filtering. Cisco suggests that the largest networks currently require no more than three layers of filtering. Because a hierarchical layer in the network topology is a control point for traffic flow, a hierarchical layer is the same as a routing layer. Thus, a layer of hierarchy is created with the placement of a router or, more recently, a Layer 3 switching device. The number of hierarchical layers that you need to implement in your network...

How Policy Based Routing Works Using Route Maps

The following list tells how policy-based routing works using route maps Policy-based routing is applied to incoming packets. When a packet is received on an interface with policy-based routing enabled, it goes through this procedure. If there is a match and the action is to permit the route, then the route is policy-routed in accordance to the set command. If there is a match and the action is to deny the route, then the route is not policy-routed but is passed back to the forwarding engine....

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. If the opportunity presents itself, practice the commands and configurations in a lab environment. Use the diagram in Figure 2-1 to guide you...

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...

Incomplete Routing Tables

The application may be unaware that it did not receive all the data this missing data may just appear as an error or may have more subtle and insidious effects. For example, if the routing table of an intermediate forwarding device such as a router is incomplete, it may make inaccurate forwarding decisions, resulting in loss of connectivity or even the dreaded routing loop (see Figure 2-2). Using the case study earlier in this chapter, if the WAN connection between the campus site and the...

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...

IP Helper Address

The IP helper address removes the broadcast destination address of a UDP packet received on an identified interface and replaces it with a specific destination address. The router has been programmed to say, If a broadcast comes in on this interface, forward it to this destination address, where the destination address is that of the server. A helper address is configured on the incoming interface. The destination address may be either an individual server or a subnet address. Multiple helper...

Ive Taken the Cisco Networking Academy Courses Now What

First, I'll start by congratulating you on having the foresight to get into the Cisco Networking Academy program we need more people that can make this stuff work For those of you who are did not take the Cisco Networking Academy track and are wondering what it is, visit for more information. Thankfully, the Networking Academy curriculum does a great job of preparing you with the skills and knowledge that you need to pass the Routing exam. Unfortunately, your study was probably spread over...

Key Requirements of a Network

When designing a network, you first must define and assess customer requirements and then put together a plan to meet these requirements. Therefore, an understanding of the business structure and current data flow within the existing environment is crucial to prioritizing the requirements of the network. The relative importance of each of the following broad key requirement categories is determined by the needs of the organization in question. For example, a small, growing catering company may...

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...

Managing Network Congestion for IP

IP is generally considered a well-behaved protocol because its communication is typically peer-to-peer, removing the necessity for excessive broadcasts throughout the network. The only broadcasts are routing updates and Address Resolution Protocol (ARP) requests. These characteristics can no longer be assumed, however, as client server technologies start to offer IP as a communication protocol. It should be understood that the application demands determine the nature of the traffic on the...

Network Structures and Data Flow

For data to be sent to its destination directly, the underlying physical structure, or wiring, should support the logical structure, or the Layer 3 addressing. It also seems reasonable that this structure should reflect the organizational data flow. It would make sense for servers to be accessible to departments that share information and for the physical wiring and logical addressing to support this sharing of resources. Therefore, the servers may be physically adjacent and on the same IP...

Occasions for Using a Default Route

The obvious example of a need for a default route is when connecting into the Internet or simply out of your organization's intranet. The outside world contains many networks in the routing tables of the systems that serve it. It is not necessary for your router to know of all the possibilities available it must simply know that the door to the great outdoors will suffice. Another occasion for configuring a default route would be for a stub network to connect to the larger network. Both these...

Optimizing the IP Address Space

Particularly in the use of WANs, where there is a predominance of point-to-point connections, allocating an entire subnet is very wasteful. VLSM allows refinement of the address space to exactly that which is needed and no more. As demonstrated, dealing with the use of VLSM to support the hierarchical design requires the consideration of the entire network topology. When using VLSM to optimize the IP address space, the network addressing can become extremely confused if it is not clearly...

OSPF Neighbors

A neighbor in OSPF is a router that shares the same network link. This is the same physical segment. A router running OSPF discovers its neighbors by sending and receiving a simple protocol called the hello protocol. A router configured for OSPF sends out a small hello packet periodically (10 seconds is the default on broadcast multiaccess media). It has a source address of the router and a multicast destination address set to AllSPFRouters (224.0.0.5). All routers running OSPF (or the SPF...

OSPF Network Topologies

Figure 5-2 A Broadcast Multiaccess Network Point-to-point This technology is used where there is one other system directly connected to the transmitting or receiving router. A typical example of this is a serial line. OSPF has no need of a designated or backup designated router in this scenario. Network traffic uses the multicast address for OSPF AllSPFRouters, 224.0.0.5. Figure 5-3 illustrates a point to point network. Point-to-multipoint This is a single interface that connects to many...

OSPF over an NBMA Network

Another design consideration is the design of the NBMA network as part of the OSPF domain. There are two main ways to approach the inclusion of an NBMA network The NBMA network can be created as Area 0. The reasoning is that if the NBMA is used to connect all remote sites, all traffic will have to traverse this network. If the remote sites are made satellite areas, then all traffic will have to traverse the NBMA, so it makes sense to make it the backbone area. This works well in a full-mesh...

OSPF Terminology

OSPF is an open standard link-state routing protocol for IP. As such, it has clear documentation that is freely available, allowing it to be offered by every vendor. This means that it can be used to connect various technologies and vendor solutions. OSPF is a sophisticated protocol, but it is in essence quite straightforward. Rather like a Russian novel of the nineteenth century, when you know the different names of the protagonists and how they interrelate, the rest is simple. Table 5-2...

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...

Placement of Client Server

The location of the servers in relation to the clients dramatically affects the traffic patterns within the network. The current philosophy is to create server farms so that the servers can be centrally administered. If the client finds the server via broadcasts, however, a serious problem will arise if there is a router between the broadcasts Because routers are a natural broadcast firewall, they treat broadcasts as an unknown address and discard them. In such a scenario, the client sending a...

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 Routing Protocols

It is rare to find just one routing protocol running within an organization. If the organization is running more than one routing protocol, it is necessary to find some way of passing the networks learned by one routing protocol into another so that every workstation can reach every other workstation. This process is called redistribution. Although the organization as a whole has one routing domain, each routing protocol considers the routing updates as propagated by another domain or...

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...

Redistribution from BGP4 into an IGP in an Organizational Network

If IBGP-4 is not fully meshed and the autonomous system is multihomed, then redistribution from BGP-4 into the IGP is needed. The IGP needs to carry the external routes across the autonomous system to the other BGP-4 router. Also, any device wanting to connect to the Internet needs to have either a default route or specific routes to direct traffic forward. Filtering must be configured otherwise, the internal routing tables will become overwhelmed. This is illustrated in the Figure 9-10. Figure...

Removing a Path or Router from the Topology Table

This process is far more complex and gets to the crux of EIGRP. The following process uses Figure 7-6 and Figure 7-7 and focuses on Router D If a network connected to Router A is disconnected, Router A updates its topology and routing table, and sends an update to its neighbors. Figure 7-7 EIGRP Maintaining the Topology Table, Router D Figure 7-7 EIGRP Maintaining the Topology Table, Router D When Router D receives the update, it updates the neighbor table and the topology table. As a router,...

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

Routing Table Codes

Table 6-5 shows the codes used in the routing table. Table 6-5 OSPF Routing Table Codes And Associated LSAs This is generated by the router, listing all the links to which it is connected, their status, their and cost. It is propagated within the area. This is generated by the designated router on a multiaccess LAN to the area. LSA Type 3 includes the networks or subnets within an area that may have been summarized and that are sent into the backbone and between ABRs. LSA Type 4 is information...

Routing Updates from Multihomed Connections to the Internet

Table 9-11 summarizes the different approaches to obtaining routing information from the Internet. Table 9-11 Receiving Routing Updates from Multiple ISPs Table 9-11 Receiving Routing Updates from Multiple ISPs Table 9-11 Receiving Routing Updates from Multiple ISPs (Continued) Table 9-11 Receiving Routing Updates from Multiple ISPs (Continued)

Rules of Policy Routing

Some rules are associated with Policy routing. The following rules seem repetitive, but, in fact, each point raises a subtly different nuance Traffic can be directed on either the source address or both the source and destination addresses. Policy routing affects only the next hop in the path to the destination. Policy routing does not affect the destination of the packet. It affects the path used to get to the destination. Policy routing does not allow traffic sent into another autonomous...

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 101 Answers

1 Issue the configuration commands for the RIP network to be redistributed on Router A into EIGRP. router eigrp 300 network 210.77.8.0 redistribute rip 2 Ensure that the interfaces running EIGRP do not have RIP updates generated through them or that the RIP interfaces do not have EIGRP updates running through them. router eigrp 300 network 210.77.8.0 redistribute rip 3 The site running IGRP and the site running EIGRP are running different autonomous system numbers. How would you implement a...

Scenario 102 Answers

1 The hospital policy states that the FTP traffic from the x-ray department (201.77.11.0 24) should be forwarded to the Biggun Server at 201.77.12.79 and that it should be sent across the leased line, which is a T1 connection. What would the configuration look like The configuration would be as follows interface e0 ip address 201.77.11.1 255.255.255.0 ip policy route-map xray access-list 101 permit tcp 201.77.11.0 0.0.0.255 eq ftp any access-list 101 permit tcp 201.77.11.0 0.0.0.255 eq ftp-data...

Scenario 111 Answers

Offer some reasons why the routing protocol Enhanced IGRP has recently been implemented in the network, and give the reasons for its deployment in that particular area of the network. Enhanced IGRP is being run across the Frame Relay WAN in areas where there are no client or server workstations. The network routers are all Cisco devices, which understand Enhanced IGRP. Using Enhanced IGRP is far more efficient on a WAN because incremental updates can be sent across the limited bandwidth. In...

Scenario 113 Answers

1 Create a transition plan, showing how the final design will be implemented. Figure 11-4 shows the answer to this question. Figure 11-4 Answer Diagram for Scenario 11-3, Question 1 In Figure 11-4, the transition would start at the core and move down to the distribution layer routers. The first move would be to place EIGRP in the Frame Relay cloud to alleviate the network overhead. After this is operational, the second phase would be to implement EIGRP in the FDDI ring because there are no end...

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 22 Answers

1 Write the access list(s) to achieve this, and apply them to the appropriate interface(s) of the appropriate routers(s). To permit access from anywhere in the lab for only the administrator, you must apply extended access lists to the fddi 0 interface of Router Y. The access lists would be applied in both the inbound and outbound directions. A diagram has also been included to show the configuration in a simpler environment. The administrator may well be working from home and dialing in to the...

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...