Cisco Config Maker

Cisco ConfigMaker is a freely available, easy-to-use Microsoft Windows application that is used to configure a small network of Cisco routers. It can run on Windows 98, Me, NT4, or 2000, offering a GUI alternative to the existing Cisco command-line interface (CLI). ConfigMaker enables Cisco resellers or end users to configure one or a network of Cisco routers, Cisco access servers, Cisco Micro Hubs, Cisco Micro Switches, or Cisco Micro Webservers. You can download ConfigMaker from the following...

Step 2 Develop the Network Topology

When designing an OSPF network, this step covers the process of determining the network's physical layout. Two common design topologies exist meshed and hierarchical. The following sections discuss each topology and help you determine which is the most efficient design for today's networks. Going into Step 2, you have developed a list of the requirements associated with the OSPF network. You have also begun to determine the financial costs associated with the network. These costs might include...

Router Identification

Every router running OSPF within a network must have a unique router ID (RID). This identification is a 32-bit number that identifies one router to another router within an AS. The RID is used by the OSPF link-state database (LSDB) as a method of tracking each router within the AS and the links that are associated with it. This identification number is unique to each OSPF router. You can use several methods to determine how your network decides upon the OSPF RID. To determine the RID, OSPF uses...

Types of OSPF Packets

OSPF uses five different packets in its protocols. Table 3-2 describes the different OSPF packet types. This section discusses each protocol and the role that the packets play. Table 3-2 Overview of OSPF Packet Types Table 3-2 Overview of OSPF Packet Types Requests LSAs that need to be downloaded to requesting router. Only sent during Exchange, Loading, or Full state. Contains a list of the LSAs that are to be updated. Often used in flooding, as discussed later in this chapter. Acknowledges the...

Types of OSPF Routers

Four different types of routers designate the hierarchical routing structure used by OSPF. Each router has a unique role and set of defining characteristics within the hierarchy. Figure 2-9 shows a typical OSPF network, with multiple areas containing the different types of OSPF routers. Link to Another ' Autonomous i System (AS) ASBR Autonomous System Border Router ASBR Autonomous System Border Router The following sections provide general descriptions for the four types of OSPF routers....

Ignoring Mospf Lsa Packets

Cisco routers do not support LSA Type 6 multicast OSPF (MOSPF), and they generate syslog messages if they receive such packets. If the router is receiving many MOSPF packets, you might want to configure the router to ignore the packets and thus prevent a large number of syslog messages. To do so, use the following command in router configuration mode To configure the router to suppress the sending of syslog messages when it receives MOSPF packets, enter the following code

Exchange Process Protocol

When two OSPF routers have established bidirectional (two-way) communication, they synchronize their routing (link-state) databases. For point-to-point links, the two routers communicate this information directly between themselves. On network links (that is, multiaccess network either broadcast or nonbroadcast), this synchronization takes place between the new OSPF router and the DR. The exchange protocol is first used to synchronize the routing (link-state) databases. After synchronization,...

Using Route Maps to Protect Against Routing Loops

This section shows you the configuration steps used to deploy route maps to stop routing loops from occurring. At first, you have the same basic redistribution configuration as shown in Example 6-49. You build the route map from this base configuration. Example 6-49 Beginning Basic Redistribution Configuration To configure the route map to protect the networks from route feedback and thus the creation of a routing loop, take the following steps Step 1 List all the networks to be permitted...

Default Routes

The capability to generate and redistribute default routes is of extreme importance within any large network. The most common method of generating a default route is through the use of a static route statement within the router. An ASBR can be forced to generate a default route into an OSPF network (domain). Whenever you configure the redistribute command or the default information originate command into OSPF, the router becomes an ASBR. An ASBR in OSPF does not by default distribute a default...

Configuration Example 4 Redistributing OSPF and EIGRP

EIGRP is a popular routing protocol for those wishing to deploy a single-vendor network (and obviously that vendor is Cisco). Is that a smart move That is a Layer 8 political discussion. Having options and flexibility does not mean that you only look at buying one vendor's product. I like Cisco equipment and Cisco's routing protocol EIGRP, but having both together puts too many constraints on the business of running a network. The use of EIGRP is solid, and it is useful to understand how to get...

Area Range

There are several key considerations when setting up your OSPF areas for proper summarization. OSPF route summarization occurs in the ABRs. OSPF supports variable-length subnet masks (VLSMs), so it is possible to summarize on any bit boundary in a network or subnet address. OSPF requires manual summarization. As you design the areas, you need to determine summarization at each ABR. Four potential types of routing information exist in an area and are listed in Table 5-13. This table shows the...

How to Configure LSA Group Pacing

OSPF LSA group pacing is enabled by default. For typical customers, the default group pacing interval for refreshing, checksumming, and aging is appropriate, and you do not need to configure this feature. The pacing interval is configurable it defaults to 4 minutes, which is randomized to further avoid synchronization. The group pacing interval is inversely proportional to the number of LSAs that the router is refreshing, checksumming, and aging. For example, if you have approximately 10,000...

SPF in Operation

The ARPAnet used one of the first distance vector routing protocols. This protocol evolved into RIP, which is still in use today. Serious limitations were encountered with RIP as networks grew. This caused a demand for a new protocol that could run within an AS and had the capability to grow (scale) to a large-sized network comprised of many routers and network links. Into this gap stepped OSPF version 1, published as Request for Comments (RFC) 1131 in October 1989 by the OSPF Working Group of...

New WAN Requirements

Terrapin wants to remove the leased lines and 3174 cluster controllers and to network its sales offices using Frame Relay. The new WAN must seamlessly integrate into the existing corporate internetwork. Be aware of the following items from a WAN design perspective The existing corporate campus network infrastructure is 10-Mbps Ethernet, with an established router base of 30 Cisco routers of various models. The current network protocols in use are IPX RIP and TCP IP with Interior Gateway Routing...

Case Study Developing the Link State Database

Earlier in this chapter, you learned how LSAs were used to send information about the links between OSPF routers. These LSAs are stored in the router in a database with each LSA as a record in that database. Figure 2-16 shows the OSPF network topology for this case study. Figure 2-16 OSPF Network Topology for Link-State Database Case Study Example 2-6 shows entries generated by the show ip ospf database command from the router HAL9000. Example 2-6 Viewing the LSA Database for the HAL9000 Router...

Neighbor Stuck in Init STATE

The init state indicates that a router sees Hello packets from the neighbor, but two-way communication has not been established. A Cisco router includes the router IDs of all neighbors in the init (or higher) state in the neighbor field of its Hello packets. Example 3-15 shows sample output of the show ip ospf neighbor command. Example 3-15 Output from the show ip ospf neighbor Command For two-way communication to be established with a neighbor, a router must also see its own router ID in the...

Configuration Example 1 Area Summarization

To take advantage of summarization, network numbers in areas should be assigned contiguously so that you can lump these addresses into one range or block when summarizing them. Figure 7-2 illustrates an example of summarization. Review the figure, and then read the explanation of what is happening. Configure Summarization Here on ABR for Area 1 Configure Summarization Here on ABR for Area 2 Configure Summarization Here on ABR for Area 1 Configure Summarization Here on ABR for Area 2 Range of...

Benefits of Summarization

Summarization, in general, provides many benefits to your network and its operation some of these benefits are apparent and others have a smaller impact on the health of network. There are four primary reasons to implement proper summarization Shrink the routing table This benefit should be clear to you after the preceding discussion. The use of summarization allows a smaller number of route entries in your table, with the added benefits of decreasing the amount of memory used. Specifically, it...

Type 5 Autonomous System External LSAs

Type 5 LSAs are generated by the ASBRs. These LSAs describe routes to destinations that are external to the AS. Type 5 LSAs are flooded everywhere, with the exception of stub areas. External links are an indication of networks outside of the OSPF routing process in the AS. These outside networks can be injected into OSPF via different sources, such as static and redistribution. The ASBR has the task of injecting these routes into an AS. Figure 3-9 illustrates the operation of Type 5 LSAs....

OSI Reference Model Layers and Information Exchange

The seven OSI layers use various forms of control information to communicate with their peer layers in other computer systems. This control information consists of specific requests and instructions that are exchanged between peer OSI layers. Control information typically takes one of two forms Headers Appended to the front of data passed down from upper layers Trailers Appended to the back of data passed down from upper layers OSI layers are not necessarily required to attach a header or...

LSA Operation Example

Now that all nine implemented LSAs have been discussed and you understand how they operate within the OSPF functional environment, refer to Figure 3-15 for a visual representation of the operation and interaction among the various types of LSAs within an OSPF network. Type 5 LSAs are flooded to all areas. Type 5 LSAs are flooded to all areas. Type 4 ASBR Summary LSAs are sent to describe the ASBR by the ABRs. Type 3 ABR Summary LSAs are sent describing the networks, but only to the area that...

Multiple Community Strings

For SNMPvl operation, Cisco permits multiple community strings so that a router can belong to multiple communities. An SNMP community string is simply a password in the sense that if you know the community string, you can access SNMP data. Furthermore, community strings can be either read-only or read write. This feature provides further security by restricting the capability to alter the configuration of Cisco devices to those that have the community string assigned the read write capability....

Link State Versus Distance Vector Routing Protocols

This section describes the two most common and relevant routing protocols that TCP IP has available for use, namely RIP and OSPF. Controversy surrounds the debate over link-state versus distance vector routing algorithms regarding which is better. NOTE Link-State and distance vector routing protocols are also known as interior gateway protocols (IGPs) this concept is discussed later in the discussion of OSPF and border gateway protocol (BGP) interoperability. Chapter 7, Summarization, discusses...

Link State Database Size Considerations

Issues relating to the size of the LSDB are important and deal directly with the LSDB operation in relation to the topology of the network. The LSDB is everywhere within an OSPF network, and the LSDB has the following functional characteristics, which do not change A router has a separate LSDB for each area to which it belongs. All routers belonging to the same area have an identical LSDB. A router performs separate SPF calculations on associated LSDBs for each area. LSA flooding occurs only...

Final Router Example Configurations

This section contains the final router configurations used in the many configuration examples in this chapter and in Chapter 7. Some valuable alias commands are included in these examples. interface Loopback0 ip address 128.213.96.100 255.255.255.0 interface Loopbackl ip address 128.213.97.100 255.255.255.0 interface Loopback2 ip address 128.213.98.100 255.255.255.0 interface Loopback3 ip address 128.213.99.100 255.255.255.0 interface Ethernet0 no ip address shutdown interface Ethernet1 no ip...

Stub Area Design Golden Rules

Many stub area design rules are in place because a stub area is designed and configured not to carry external routers. If a situation occurred within a stub area that caused external links to be injected into the area, the stub area's usefulness is ruined. The following are the stub area design golden rules A single ABR is needed for a stub area, but if there is more than one ABR, accept nonoptimal routing paths. No ASBRs can be within a stub area. No virtual links are allowed to transit the...

Summarization with OSPF

IP address assignment and route summarization are inextricably linked when designing OSPF networks. To create a scalable OSPF network, you should implement route summarization, thus allowing you to reduce the memory requirements on a router. You must exercise caution and consider the impact of a large number of route entries if you are not going to use summarization. To create an environment capable of supporting route summarization, you must implement an effective hierarchical addressing...

Case Study OSPF Initialization

This case study puts all the pieces together into a coherent overview of OSPF initialization and beginning operation. To do this, you take a pair of routers that are connected together via an Ethernet connection to form the OSPF backbone, Area 0. Each router is also connected to other OSPF areas, as shown in Figure 3-28. For brevity, only those packets that prove a concept or step are included. NOTE To capture everything needed to demonstrate this case study, the routers were correctly...

Case Study OSPF with Multiple Areas

In this case study and throughout the next several case studies, you review a series of network scenarios that implement and build on the OSPF technologies discussed in the previous several chapters. This case study evaluates the configuration of OSPF and three routers into a multi-area OSPF network design solution, as shown in Figure 5-28. Case Study OSPF with Multiple Areas 331 First, configure IP to get the network running and assign interfaces as well as loopback interfaces. In this...

Area Configuration

Areas have additional roles and functions similar in scope and purpose to OSPF route types. This section discusses OSPF areas and how to configure them within OSPF. You should review OSPF Areas in Chapter 2 and Area Design in Chapter 4. You should know how to activate a basic OSPF area by using the network command, as described earlier in this chapter. To configure a normal OSPF area, the network command is used when in OSPF router configuration mode. Example 5-6 initializes OSPF routing...

Even More ECMP

OSPF performs ECMP per destination over up to four paths to a destination, but what happens when you have five or even six equal-cost paths do they go unused Absolutely not The maximum-path command, when applied to OSPF, allows you increase from four to six the maximum number of paths supported. The example that follows shows this in action with OSPF. In Example 5-32, eight ECMPs route to network 192.168.1.0 from Router 1 to Router 2 have been configured. By default, OSPF places four ECMP route...

Types of Network Topologies

The preceding sections discussed the evolution of today's advanced networks and the building blocks that have evolved to make them what they are today that is, the OSI reference model and the TCP IP protocol. The sections on the OSI reference model described the essential means of how data is transported between the various layers that are running on all intranet devices. The TCP IP section reviewed the protocols' characteristics. This section addresses the media that operates in your network....

Altering OSPF Convergence

One of the most attractive features of OSPF is its capability to quickly adapt to topology changes. The two essential components to routing convergence are as follows Detecting changes to the network topology Rapid recalculation of routes OSPF uses the following mechanisms to detect topology changes Interface status changes (such as carrier failure on a serial link). The failure of OSPF to receive a Hello packet from its neighbor within a specified timing window, called a dead timer. Both of...

Verifying OSPF Operation

After you enable OSPF routing on each of the three routers, verify its operation using show commands, as demonstrated in Example 2-10. Invalid after 0 seconds, hold down 0, flushed after 0 With this command output, you can gain some useful data regarding the operation of OSPF in your network. You can see the networks that OSPF is routing as well the RIDs of the other routers in the network that have sent routing information. The output from the show ip ospf command, as demonstrated in Example...

Configuring OSPF Authentication in an Area

Review for a moment why you would want to configure OSPF authentication. You want to protect and preserve the routing updates that flow between our routers, but why Someone might spoof routing updates, which leads you to the conclusion that if someone could gain access to spoof your routing updates, protecting him her with a plain text password is useless. A nice side benefit of this configuring section is that if you understand MD5 you should have no difficulty with plaintext which is less...

Distribute Lists and OSPF

This chapter has already mentioned many of the difficulties with distribute lists and how Cisco has designed them to interact incorrectly with OSPF. While the recommended practice is to use route maps instead of distribute lists whenever possible, distribute lists still have their place. This section discusses how to configure them correctly to perform route filtering. You are going to use this gotcha with OSPF and distribute lists to accomplish the mission at hand and in the process find out...

Different Network Types and OSPF

There are three distinct classifications of physical network media that OSPF can differentiate between. Each of these network types requires a slightly different configuration to optimize the performance of OSPF. Configuring your OSPF network type is one of the most prominent features of OSPF. The strength of OSPF lies in its flexibility to meet certain network design requirements. The following sections show you how to customize OSPF to your network's design. Cisco IOS Software allows five...

Foundations of Networking

Many advanced features are being supported by the physical hardware through the application of Moore's law. Those of us responsible for networking these many devices follow a theoretical framework that allows the required functionality to be deployed within our networks. This framework is more commonly known as the OSI reference model. OSI stands for open system interconnection, where open system refers to the specifications surrounding the model's structure as well as its nonproprietary public...

Implementing Your Design

Ospf Addressing Block

This section discusses some of the design topics to consider within this case study and how to implement them in the network given the preceding discussion. These can be both OSPF-specific topics and other all-encompassing network issues, such as IP addressing. You are able to obtain a contiguous block of 32 Class C ( 24 or 255.255.255.0 mask) subnets for this network from the IP address manager. The address block is 172.17.64.0 19, which allows clean summarization into the backbone area after...

Understanding the Seven Layers of the OSI Reference Model

Osi Reference Model Layers

The seven layers of the OSI reference model can be divided into two categories upper layers and lower layers. The upper layers are typically concerned only with applications, and the lower layers primarily handle data transportation. The sections that follow examine the three upper layers, the four lower layers, and the functions of each. The upper layers of the OSI reference model 5, 6, and 7 are concerned with application issues. They are generally implemented only in software programs. The...

Distribute List Concerns

This is an important point to note regarding the operation of OSPF. Recall that redistribution occurs on an OSPF ASBR because in OSPF an ASBR connects to other routing domains. This concept will become important shortly. There are two ways to apply a distribute list on a router To affect routing updates coming inbound Applied outbound to affect the routing updates be sent by the router. Use the following commands to achieve applying a distribute list distribute-list out When applying a...

TCPIP Protocol Suite

A protocol is a set of rules and conventions that govern how devices on a network exchange information. This section discusses one of the more commonly used protocol suites TCP IP. This discussion does not provide sufficient information for an in-depth study of TCP IP. Nevertheless, TCP IP needs to be covered to some degree so that you can better understand the overall operation of network protocols these discussions are expanded in later chapters concerning OSPF. The TCP IP protocol suite is...

Understanding LSA Group Pacing

The OSPF LSA group pacing feature allows the router to group OSPF LSAs and pace the refreshing, checksumming, and aging functions. The group pacing results in more efficient use of the router. NOTE Cisco has made LSA group pacing the default behavior for OSPF in Cisco IOS Software Each OSPF LSA is recorded and tracked with an age that indicates whether the LSA is still valid. When the LSA reaches the maximum age (60 minutes), the LSA is discarded from the link-state database. A router keeps...

IP Addressing

This section discusses IP addressing methodology, basic subnetting, variable-length subnet masking (VLSM), and classless interdomain routing (CIDR). In a properly designed and configured network, communication between hosts and servers is transparent. This is because each device that uses the TCP IP protocol suite has a unique 32-bit IP address. A device reads the destination IP address in the packet and makes the appropriate routing decision based on this information. In this case, a device...

Normal NSSA Operation and Configuration

Table 5-11 presents shows which LSAs are active in a normal NSSA. Table 5-11 LSA Operation in a Normal NSSA Router link connected intra-area routes ABR summary links inter-area via ABR AS external links external routes via ASBR Not-so-stubby areas NSSA routes via ABR In Figure 5-16, you can see how and where the LSAs are transmitted within a stub area. When configuring an area as an NSSA, all routers in the area must be configured to identify the area as an NSSA. In Example 5-13, you change...

Configuration Example 3 Redistributing Connected and Loopback Interfaces

This example looks at redistributing connected networks into OSPF, the results of this, and alternative ways of handling connected networks. In cases where you must redistribute connected networks into OSPF instead of configuring OSPF to recognize them via the network command, all the connected networks show up as external routes in OSPF. In this example, Router Neo is configured with a loopback interface, which is assigned the network 192.168.253.0 24. Figure 6-11 shows the overall network for...

Configuring OSPF Authentication on a Virtual Link

In this case, because a segmented area 0 with a virtual link exists, OSPF authentication is configured in both area 0s. That is the right thing to do because through the virtual link, the two area 0s think they are one and the same, and as discussed earlier, OSPF authentication is turned on in an entire area. However, after checking the network after configuring OSPF authentication, notice that many routes have disappeared from router Neo. Example 8-7 Neo's IP Routing Table Is Missing Some...

OSPF Routing Concepts

OSPF is a dynamic link-state routing protocol that uses a link-state database (LSDB) to build and calculate the shortest path to all known destinations. It is through the use of Dijkstra's SPF algorithm that the information contained within the LSDB is calculated into routes. The shortest path algorithm by itself is quite complicated, and its inner workings were covered in depth in Chapter 3, OSPF Communication. It is important to have a good understanding of Dijkstra's SPF algorithm to achieve...