Change in the Network

A change in the network topology also necessitates information to be propagated through the network. For example, the rest of the network notices that a new router has joined their ranks. A particular router that notices a change floods the area with the update so that all routers can alter their routing tables to reflect the most current and accurate information. Different techniques are used for these different routing table requirements. Essentially, the difference between the two techniques...

Change in the Network Maintaining the Topological Database and the Routing Table

Now turn back to the 2500 router in Building A of the San Francisco campus in Figure 5-6. The router is now happily a member of the OSPF network. Now follow the process of hearing an update to the network in the form of an LSA. As soon as a router realizes that there has been a change in the network topology, the router is responsible for informing the rest of the routers in the area. Typically, it will identify a change in the state of one of its links for one of the following reasons The...

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 will select one path to enter the routing table from several paths offered by multiple routing protocols. In Figure 4-2, 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...

Aggregating Routes

To summarize or aggregate routes within the BGP-4 domain, use the following command from the config-router mode aggregate-address ip address mask summary-only as-set If the parameter summary-only is used, then the specific routes are suppressed and the summary route is the only one propagated. If the parameter as-set is used, then all the autonomous systems that have been traversed will be recorded in the update message. This is the default configuration. Because it may be necessary to...

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...

ANDing Example

Figure 3-2 illustrates the ANDing logic. Figure 3-2 AND Logic and the Subnetwork IP address in binary 10010000.01100100.00010000. 00001000 IP subnet mask in binary 11111111.11111111.11111111. 00000000 The result of the logical AND 10010000.01100100.00010000. 00000000 Layer 3 can now make a decision on how to route the network number that has been revealed. The result is the removal of the host portion of the address, and the subnet address is left intact. Therefore, the host 144.100.16.8 is a...

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...

Authors Note About Exam Content

As Cisco's authorized external publishing company, Cisco Press is the only publisher that is partnered with Cisco. Cisco has shared other information with Cisco Press, part of which includes some details that are expected to be posted on Cisco's web site at a later date. At press time, Cisco had not finalized what other details about the exam will be posted on its web site, so I cannot list any of those details here. Fortunately, what does get posted by Cisco will be easily available to you I...

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...

Backup Designated Routers

The previous paragraph is only a half truth because there has been a lot of effort put into ensuring that the network does not fail. It is a little nerve-racking for the network administrator to have the responsibility of the segment fall to one router. This poses the frightening situation of a single point of failure, a term that raises the blood pressure of any of those in charge of the network. Redundancy has been built into the network with the backup designated router. Just like an...

Bandwidth Control

A perennial concern of network administrators is the amount of bandwidth used for overhead traffic. Administrators want to minimize the amount of network control traffic sent through the network, to maximize the bandwidth available for user data. One of the major benefits of both EIGRP and OSPF is that they send as little network traffic as possible. This has the advantage of decreasing the convergence time of the network and ensuring that the network traffic that is sent arrives at the...

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...

BGP4 Policy Based Routing

Policy-based routing gives the administrator the ability to define how traffic will be routed at the autonomous system level. This is a level of control above the dynamic routing protocol. Given that many variables in BGP-4 can influence dynamic routing (these are called variables), this is a very high level of control. This other dimension distinguishes BGP-4 from other routing protocols. Policy-based routing is a form of static routing enforced by specialized access lists called route maps.

BGP4 show Commands

Example 9-9 shows a list of all the show commands available to the BGP-4 administrator. Example 9-9 BGP-4 show Command Options A.B.C.D Network in the BGP routing table to display cidr-only Display only routes with non-natural netmasks community Display routes matching the communities community-list Display routes matching the community-list dampened-paths Display paths suppressed due to dampening filter-list Display routes conforming to the filter-list flap-statistics Display flap statistics of...

Bit Allocation the Subnet Rule and VLSM

In truth, the subnet does have to conform to the rule as described. With VLSM, however, it is often forgotten that the entire subnet area is considered one subnet. Therefore, the rule must be obeyed once, not on each instance of variable subnetting. In the preceding example, you would choose to obey the rule either in the bits allocated to the region, campus, or building, but not in each hierarchical layer. It would make most sense to adhere to the rule using the least-significant bits. In this...

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...

Case Study

As seen in the last chapter, the large multinational company Humugos has offices in 250 countries. Each country operates as a separate company, conforming to the tax and legal laws of the country. It is still important that each part of the organization must be capable of connecting to the others, but EIGRP is no longer feasible for a number of reasons. The main issue is the number of connections that each country has into the Internet. There is also some need to manipulate the traffic,...

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. attribute The metric used by BGP-4. autonomous system (AS) Definition for the organizational boundary. Within the terminology of the...

Characteristics of Route Reflectors

The following are the chief characteristics of route reflectors A route reflector is a router that forwards updates to its clients. When a client sends an update to the route reflector, it is forwarded or reflected to the other clients. The route reflector is the only router that is configured or that has the remotest idea that it is anything other than a peer. A client is a router that receives updates from a route reflector. Both a route reflector and a client, therefore, form a unit that...

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....

Classful Routing

Classful IP routing protocols include RIPv1 and IGRP. The characteristics of a classful routing protocol are listed here Summarization occurs at the network boundary. Routes exchanged between foreign networks are summarized to the NIC number network boundary. Within the same network (NIC number), subnet routes are exchanged by routers, without the mask. The subnet mask is assumed to be consistent for a NIC number used within a network, so all router interfaces must share the subnet mask for...

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 Commands for a Multiarea OSPF Network

The following commands are necessary to configure a multiarea OSPF network The OSPF area range command for an ABR The OSPF summarization command for an ASBR The OSPF command for a stub area The OSPF command for a totally stubby area The OSPF command for the cost of a default route propagated into the area The command for configuring a virtual link

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 IP Helper Address

The syntax for the ip helper-address command is as follows ip helper-address address The IP helper address forwards broadcasts for the following UDP ports NetBIOS datagram service (138) In addition to the helper address, the IP forward protocol instructs the router to forward broadcasts. By stating the port number, particular types of broadcast may be identified. This is very useful when used in conjunction with the helper address because it identifies those broadcasts to be readdressed to...

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 Bandwidth over a Hybrid Multipoint Network

If the multipoint network has differing speeds allocated to the VCs, a more complex solution is needed. There are two main approaches. To take the lowest CIR and to simply multiply this by the number of circuits. This is applied to the physical interface. The problem with this configuration is that the higher-bandwidth links will be underutilized for some things. If possible, it is much easier to configure and manage an environment that has used subinterfaces, where a VC is logically treated as...

Configuring EIGRP

The commands for EIGRP are consistent with the other IP routing protocols. Although IP routing is on automatically, the chosen routing protocol must be configured and the participating interfaces must be identified. EIGRP allows for VLSM and, therefore, summarization because the mask is sent in the update packets. Although summarization is automatic, EIGRP summarizes at the NIC or major network boundary. To summarize within the NIC number, it must be manually configured. Unlike OSPF that can...

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...

Configuring the Default Metric for Ospf Rip Egp or BGP4

Alternatively, it is possible to redistribute the routing protocol and then, with a separate command, to state the default metric. The advantage of this is it is a simpler configuration visually, which is helpful in troubleshooting. Also, if more than one protocol is being redistributed into the routing protocol, the default metric applies to all the protocols being redistributed. To configure the default metric for OSPF, RIP, EGP, or BGP-4, use the following command syntax The default-metric...

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...

Design Points for the Pointto Multipoint Mode

By default, the network is considered to be a series of point-to-point interfaces. There is no need to specify neighbors because the neighbors will see each other and simply become adjacent, with no need for the election of a DR or a BDR. However, you can specify neighbors with the neighbor command, in which case you should specify a cost to each neighbor. You are not required to have a fully meshed topology, which reduces the number of PVCs needed and the number of neighbor entries in the...

Designing and Configuring a Scalable BGP4 Network

It is ironic that the opening section in a chapter dealing with the configuration of a sophisticated and large network using BGP-4 should have to discuss the problems that the protocol has with managing the routing information across a large network. After all, BGP-4 was designed for use in the Internet, the largest network of all. In reality, it comes down to design and the truism that most things used inappropriately can be transformed from a life-giver to an instrument of death. Consider the...

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...

EIGRP and the Use of the bandwidth Command in WANs

The developers of EIGRP have provided configurations to suit the three different WAN environments. The three WAN environments are as follows NBMA, such as Frame Relay, X25, or ATM NBMA hybrid (this is a combination of the point-to-point and multipoint When configuring the bandwidth command, it is important to consider the actual speed of the link. It is practical to configure this only on serial lines, where the speed of the link will vary considerably. However, do not confuse the speed of the...

EIGRP Defined

The focus of this chapter is on how EIGRP works so that those networks can be designed to maximize efficiency and truly scale the network. The major concern in scaling an organizational network is controlling the network overhead that is sent, in particular over slow WAN links. The less information about the network, its services, and networks that need to be sent, the greater the capacity available for the data between clients and servers. Although sending less routing information relieves the...

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...

Enhanced Interior Gateway Routing Protocol

EIGRP was designed to make efficient use of the available network bandwidth. The routing protocol can be used for IP as well as AppleTalk and IPX. The advantage of EIGRP is that it is incremental, sending updates only when a change in the network is experienced. EIGRP is particularly efficient in sending network and server information for such client server products as NetWare for IPX and AppleTalk because it automatically redistributes routing updates into the local protocol updates. EIGRP is...

Excessive Traffic

If the traffic volume outgrows the network, the result is congestion. When this occurs on a single segment, the capacity of the medium overrun resulting in the dropping of packets and the medium can react adversely to excessive traffic. Ethernet illustrates this well. Ethernet has strict rules about accessing the medium, so, a physical problem such as extraneous noise or just too many trying to access too little results in excessive traffic, causing collisions. A collision requires all...

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...

Familiar Rules in IP Subnetting

Because originally the routing protocols could not send the mask with the routing update, the first set of rules about applying IP addresses were different than they are now. For the most part, these rules still hold true. With the advent of new technology, however, it is now possible to surmount some of the previous limitations set out in RFC 950. The earlier (and perhaps familiar) rules included the following The network bits do not need to be contiguous, although they are advised to be...

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...

Foundation Topics Introduction What Is OSPF

OSPF stands for Open Shortest Path First, an open standard link-state routing protocol. This routing protocol was built by a committee, which is why it is an open standard. The word open means that anyone can read the rules or standard and write an application. The routing protocol as such belongs to no one, but to everyone. OSPF's purpose as a routing protocol is to convey routing information to every router within the organizational network. The technology that has been selected is link-state...

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...

Hiding Network Changes

If the routing table contains a summary of the networks beneath it, any changes in the network at these levels are not seen. This is both a good thing and a bad thing. If the network in the earlier example 140.100.50.128 27, the subnet on the fourth floor of the second building in San Jose, California were to go down, the router at the core would be oblivious to the LAN problem. This is beneficial because there are no additional updates or recalculation. The disadvantage is that any traffic...

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 Prefix Lists Work

Before using a prefix list in a command, you must set up a prefix list. Each line in the prefix list is associated with a sequence number, similar to the number identifying a line of code in a computer program. The editing of the prefix list is achieved by referencing the line or sequence number. This is not available in access lists, which requires the rewriting of the entire list, unless you have the forethought to cut and paste the configuration file into a word processor. In planning the...

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 the Topology Table Updates the Routing Table

From the topology map, a routing database is constructed. This database will be unique to each router, which creates a routing database by running the shortest path first (SPF) algorithm called the Dijkstra algorithm. Each router uses this algorithm to determine the best path to each network and creates an SPF tree on which it places itself at the top or root. If there are equal metrics for a remote network, OSPF includes all the paths and load balances the routed data traffic among them....

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...

IGRP and EIGRPs Gateway of Last Resort

When default information is being passed along through a dynamic routing protocol, no further configuration is required. In the case of RIP, there can be only one default route, network 0.0.0.0. However, in the case of IGRP, several networks can offer default routes, although only one is used. If the router is not directly connected to the default network but does have a route to it, it is considered as a candidate default path. When there are multiple default routes in the routing table, the...

Implementing and Tuning BGP for Use in Large Networks

The topics in this chapter concern the advanced configuration of BGP-4. You will need to apply your understanding of the basic concepts and configuration of BGP-4 that you gained in the last chapter because, in this chapter, the full complexity and sophistication of BGP-4 is explained. In this chapter, the true use of BGP-4 is explored whether its use is to connect to an ISP or even to act as an ISP with several connected organizations. The chapter covers how BGP-4 can be configured to select a...

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...

Introduction BGP4 and Communicating with other Autonomous Systems

The BSCN course deals with connectivity to the Internet via a service provider. One of the methods used to make this connection is the external routing protocol BGP-4. The Routing 2.0 exam, recognizing that BGP-4 is increasingly important in larger environments to communicate with the Internet agent or service provider, covers a conceptual overview of BGP-4. A solid base to BGP-4 is given in addition to basic configuration commands. It is stressed however, that if your network is a simple one,...

IP Access List Overview

Access lists are linked lists with a top-down logic, ending in an implicit deny any command, which will deny everything. Top-down logic means that the process will read from the top of the access list and stop as soon as it meets the first entry in the list that matches the packet's characteristics. Therefore, it is crucial that careful attention be given to their creation. Writing down the purpose of the proposed access list before attempting to program the system also proves helpful. Access...

IP Addressing Summary

Remember these following important points regarding IP addressing The IP address is 32 bits long. The network host boundary can be anywhere in the 32 bits. The Internet allocates a unique bit pattern. These bits are the first bits on the far left and are not available for the administrator to use for networks because they identify your organization to the Internet. The Internet authority ARIN (in the United States) will provide the left portion of the address to the organization to use for...

Ive Learned a Lot About CCNP Topics Through Experience But I Will Not Be Taking the BSCN Course Now What

If you feel like you know a fair amount about professional-level routing topics already (at a level that makes taking the BSCN course not very worthwhile), but you are worried about the few topics that you simply just have not worked with, then this strategy is for you. This book is designed to help you figure out what IP routing topics you need some help with, and then help you learn about them. Here is the simple strategy for you Strategy 1 Use this book exactly as described in the opening...

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...

Ive Taken the Old ACRC Course Now What

It is true that the current version of the exam is a closer match to the BSCN class. However, if you were to compare the BSCN and ACRC courses, you would find there is much more in common than is different. In fact, more than half of the ACRC topics are retained in the BSCN course. Of course, if you retain more than 50 percent of what you heard in class, then you are an extraordinary person, so you probably still need to fill in some holes in your knowledge base. For you, the following...

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...

Learning About a Change in the Network

A router knows very quickly whether the neighbor, which may also be the next logical hop, is dead because the router no longer receives Hello protocol messages. The routing process sends out a message immediately when it identifies a problem, without waiting for the update timer to expire. This is known as an incremental update. The update contains only the relevant information. The router also remains silent if there is no change in the network. The incremental update improves convergence time...

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...