Large Scale IP

Figure 113 Comparison of Dna Iv and the OSI Model

MQP Ettoritt , FQD1 LAPtJ _ IE> ,C ttt LOHon KWT1G DOC Pi P 902.2 LLC H rty FWay Elteire Tofcen R ny FDDI i sciiif v -A 1 Ipfihvare i ls dware Therefore, there is no need for an equivalent of ARP in the DNA IV. The network-layer address is 16 bits, with the first six bits used to identify an area and the remaining 10 bits used as a node address. Addresses are usually written in the form area.node, where area is 1-, and node is 1-1023. This area node distinction enables DNA IV to perform...

Benefits of OSI

By the early 1980s, the networking community was tired of being tied to proprietary networking solutions. To promote a smoother system with more support, both hosts and networking infrastructure had to come from the same vendor. Admittedly, development according to standards could squash creativity, but from a customer perspective, this was an acceptable price to pay for establishing the data networking arena as one in which multiple vendors could play. The problem, then, was deemed a lack of...

Figure 31 Packet Switching

Packet routers in IP networks are able to detect IP packet errors, but they do not perform error correction or provide substantial congestion control (Internet Control Message Protocol ICMP source-quench messages are typically ignored by routers and host). These functions are left to the Transport Control Protocol (TCP) stack that is implemented on the hosts that connect to the network. While certain WAN technologies may implement error correction and congestion control in Layer 2, this process...

Flow Accounting and Traffic Engineering

Distance-dependent charging schemes also exist. As with telephone calls, to determine the cost of each byte, it is necessary to know where each byte originates and its destination. The origin issue seems obvious the traffic enters the network on an interface associated with a particular customer. To determine the destination, you must perform flow accounting this is where Netflow comes in. It is generally recommended that you deploy Netflow as a perimeter technology that is, enable Netflow on...

Intermediate Systemto Intermediate System

Intermediate System-to-Intermediate System (IS-IS) is a routing protocol that is based on an OSI intradomain routing protocol, and is designed for use with the ISO protocol for the Complete Sequence Number Protocol (CSNP) data unit. IS-IS may be used as the Interior Gateway Protocol (IGP) to support TCP IP, as well as the OSI. IS-IS also can be used to support pure IP environments, pure OSI environments, and multiprotocol environments. Because it supports both IP and OSI traffic, IS-IS can...

On Demand Routing

On Demand Routing (ODR) is an enhancement to an existing feature called Cisco Discovery Protocol (CDP). CDP is a protocol used to discover other Cisco devices on either broadcast or nonbroadcast media. With the help of CDP, a router can find the device type, IP address, Cisco IOS running on the neighbor's Cisco device, and capabilities of the neighbor device. The idea behind this feature is to advertise the connected IP prefix of a stub router via CDP. This new feature uses an extra five bytes...

Packet Switching Links ATM

ATM adopts a strategy of segmenting all IP packets into small, 53-byte cells carrying a 48-byte data payload. The motivation for small cells is based on minimizing packetization delay, which makes the technology suitable for time-sensitive applications. The motivation for fixed cells is to allow the switching to occur in hardware, because hardware switching of variably sized frames is more complex. The choice of small cell size has been a source of debate. Nevertheless, in local area...

The Pointto Point and Pointto Multipoint Models

By using either the point-to-point or the point-to-multipoint models, the network is more robust, and the cloud does not need to be fully meshed. Partial mesh is successful because no DR is present, so losing a PVC to the neighbor does not mean loss of connectivity. Another possibility is to reduce the full mesh. Figure 16-12 shows a reasonably small mesh. You can define this cloud as one subnet and run OSPF in point-to-multipoint mode, or you can define each one of the point-to-point...

Classful Distance Vector to Classless Distance Vector Protocol IGRP to Enhanced IGRP

In the case of Enhanced IGRP IGRP within the same autonomous system, the redistribution is automatic. Enhanced IGRP has two numeric distance values that distinguish between internal and external routes. Any route that has been redistributed into Enhanced IGRP via any other routing domain or routing protocols is considered external and has an administrative distance of 170. Any network within the Enhanced IGRP domain has a distance of 90. The administrative distance of IGRP is 100, regardless of...

The Internet NAPs

The network access points (NAPs) were intended as the key peering points for NSPs that provided core routing services for the NFSNET's regional distribution networks. The NAPs were modeled on the FIXs, which were used to connect the Big Four during the operation of the NSFNET backbone. Traffic within the NAPs, however, was supposed to operate freely of the acceptable usage policy (AUP). Although the NSF NAP Manager solicitation had some admirable goals in statistics collection and support for...

Circuit Switching Links ISDN

Integrated Services Digital Network (ISDN) is used by telephone companies to carry digitized voice and data over the existing telephone system. ISDN has emerged as one of the leading technologies for telecommuting and remote office connection into the corporate headquarters. On the seven layer model, ISDN operates at the physical, data link, and network layers. ISDN basic rate interface (BRI) provides two barrier channels (commonly referred as B channels). Each of these B channels carries data...

Configuring the Areas in OSPF

Recall that OSPF has four types of areas in the Cisco environment, which were defined in the earlier section The OSPF Area Concepts Recall that in a regular area, every link state is flooded. Configuration for regular area is simple network 131.108.0.0 0.0.255.255 area 1 External link states are not flooded in the stub area. All routers in that area need to be defined as stub. If any router within the area is not defined as stub, an adjacency is not formed. The stub area configuration is as...

Routing Policy and the BGP Decision Algorithm

A BGP router may receive paths for the same route from many neighbors. How the best path is selected is a matter of local policy. The policy within an AS must be consistent otherwise, routing loops could occur. Conceptually, the policy and decision process is shown in Figure 11-16. Figure 11-16. BGP's Policy and Decision Process An incoming Routing Information Base is maintained for each peer. Incoming policy is applied to each RIB, and complying routes are passed as candidates to the BGP...

Figure 1648 ISPnet SFO Regional Network

ISPnet LAX Regional Network Figure 16-49. ISPnet LAX Regional Network Although ISPnet consists of thousands of routers, all configurations fall into three general categories access, distribution, and backbone. The SFO regional network spans many POPS for convenience, only two are shown in Figure 16-48. Multiple technologies (serial, SMDS, and Frame Relay) are used to connect customer networks to ISPnet's access routers. Router access1.sfo is one of multiple access routers...

Figure 1650 ISPnet BGP Architecture

The generic BGP router configuration for ISPnet includes the large-scale configuration developed in Chapter 11, Border Gateway Protocol, along with a number of peer group definitions. Note that full functionality is not required for all routers, but it is beneficial to maintain a consistent configuration across the network. ISPnet extensively uses communities to color routes. In particular, the following communities are defined Communities used for BGP QoS policy propagation ip community-list...

Overview of RIP

RIP is a distance vector protocol that uses the Bellman Ford algorithm to compute the shortest route to the destination. RIP was originally designed for Xerox PARC and was used in Xerox Network Systems (XNS). It then became associated with TCP IP and the UNIX system. The protocol is one of the first dynamic routing protocols used in the Internet. It was developed as a method of passing reachability information between routers and hosts. Each entry in a RIP table contains a variety of...

Figure 62 Count to Infinity

Three additional issues with regard to RIP also must be addressed holddown, split horizon, and poison reverse Holddowns prevent regular update messages from inappropriately installing a route that has become defective. When a route is defective, neighboring routers detect it, and then calculate new routes. The routers send out routing update messages to inform their neighbors of the route changes. This update might not arrive to all the routers at the correct time, however, which causes some...

Open Shortest Path First

This chapter discusses the Open Shortest Path First (OSPF) protocol, including the following issues OSPF is a link-state protocol used as an Interior Gateway Protocol (IGP). This section discusses how OSPF builds a database and how to build routing tables from that database. Introduction to link-state protocols Link-state protocols are like a jigsaw puzzle. Each router within an area maintains information about all the links and routers in its area. This section explains the fundamentals of...

Populating Cisco Express Forwarding

CEF has two major components the forwarding information base (FIB) and the adjacency database. The FIB is the lookup table that the router uses to make destination base-switching decisions during CEF operation. This table is almost an exact copy of the routing table. (The FIB CEF table does not carry administrative distances and metrics). When the routing table topology is changed in the network, the routing table is updated and the changes are immediately reflected in the CEF table. Consider...

Flooding on Broadcast Networks

Flooding is optimal over the broadcast network when the IS creates a pseudonode. For each pseudonode, a DIS is responsible for creating and updating the pseudonode LSP and for conducting the flooding over the LAN. Unlike OSPF, there is no backup DIS. The DIS sends CSNP every 10 seconds the LSP is not acknowledged. If a router notices that part of its database is missing or that the entry in its database is old, it sends a PSNP requesting a newer copy of the LSP. The status of the SRM bit is...

External versus Internal BGP

The classic application of BGP is a route exchange between autonomous systems. However, the scalable properties of the protocol, along with the need to transit several attributes to implement routing policy, have encouraged its use within autonomous systems. As a result, as shown in Figure 11-2, there are two types of BGPs External BGP (EBGP), for use between ASs and Internal BGP (IBGP), for use within them. Figure 11-2. External BGP (EBGP) Exists between Autonomous Systems, and Internal BGP...

RIP and Classful Masks

RIP does not carry masks with the prefix information in its update. For all the network prefixes, RIPV1 assumes a natural classful mask. Therefore, RIP cannot support supernets. Supernetting, as mentioned in Chapter 2, was introduced much later, and RIP existed before classless interdomain routing (CIDR). As a protocol, RIP was designed to have natural classful masks, so RIP does not understand routes that do not have natural class masks, such as eight-bit for class A, 16-bit for class B, and...

Protocol Operation

SNMP is an application-layer protocol that facilitates the management of networking devices and services. Three versions of the protocol exist the SNMPv1 management framework is defined in RFCs 1155, 1157, 1212 the SNMPv2 management framework is defined by RFCs 1901-1908 and SNMPv3 (which at the time of this writing is still in the development phase) is defined by RFCs 2271-2275. Table 15-2 lists the RFCs applicable to each version. Table 15-2. SNMP Management Framework RFCs Introduction to...

Making the Backbone Reliable

Reliability can be acquired by employing two methods. First, you can create more reliable routers through the use of carrier-class characteristics, such as multiple CPUs, power supplies, and generators and even redundant routers. Ultimately, however, any backbone will include WAN links that rely on a great deal of equipment and environmental stability for their operation, which represents a real risk of ultimate failure. If the carrier's up-time guarantees are not sufficient, you have no choice...

Staging Configuration Upgrades

Large-scale upgrades of either configuration or IOS version should be staged. The first stage is to try the new configuration, hardware, or image in a lab. If lab trials are successful, one or two pertinent areas in the network may be used for further testing. If an upgrade involves all three software, hardware, and configuration changes, the following order is recommended Install the new image run for several hours. Install the new hardware run for several hours. Install the new configuration...

The Very High Speed Backbone Network

However, the NSF believed that certain functions could not be fulfilled by a commercial Internet. Infrastructure was one in particular, the stringent requirements of the supercomputer centers and their associated research community. NSF awarded MCI a 50 million contract to design, operate, and maintain a backbone network connecting the same supercomputer centers as the original NSFNET backbone (refer to Figure 1-4). The backbone was activated for testing in late 1994 and was officially launched...

Figure 18 Modern US Internet Architecture

Within the United States, major NSPs peer at both public and private NAPS, with most tending toward the latter. The NAPs in San Jose, Washington, Pensauken, and Chicago are still important exchange points for the major NSPs particularly for the middle-size NSPs and large federal networks. Peering always takes place via BGP. Usually, the networks fall into the three-layer hierarchical model, consisting of acore, a distribution, and an access network Peers usually connect their core routers via...

BGP Configuration Stencil for Large Networks

The following basic configuration summarizes the commentary of this section. It is not necessary to include the complete configuration as part of your default BGP configuration. You should study this section to see what is suitable for your environment router bgp 100 no synchronization bgp router-id 1.0.0.1 no bgp fast-external-fallover bgp log-neighbor-changes bgp dampening neighbor internal peer-group neighbor internal description ibgp peers neighbor internal update-source loopback0 neighbor...

Deploying Multicast in a Large Network

In this case study, you will examine the multicast architecture in a large network corresponding to an Internet service provider, ISPnet. The large network encapsulates many regional networks, each with the architecture shown in Figure 13-16. The overall network multicast architecture is shown in Figure 13-17. For simplicity, you can enable ip pim-sparse-dense-mode on all interfaces within the network and on customer interfaces, as requested by the customer. Therefore, if the customer wants...

Managing Router Access

A number of steps must be taken to control access to routers within the network. The first step is to configure access control for each individual router, as follows service password-encryption enable secret 5 3242352255 no enable password access-list 16 permit 10.0.1.0 0.0.0.255 This system is the property of ISPnet Networks. Contact noc ISP.net or call +1 555 555 5555 with inquiries line vty 0 4 access-class 16 in exec-timeout 5 0 transport input telnet transport output none password 7...

Using Virtual Profiles

These problems can be solved with a feature in version 11.3 called virtual profiles. Virtual profiles are based upon dialer profiles, so there is the abstraction of the network-layer interface from the physical ISDN circuit. However, virtual profiles expand upon dialer profiles by allowing dynamic interface configuration when an inbound call is made. The interface configuration is stored on a central server (in this case, a AAA server supporting either the TACACS+ or RADIUS protocol) and...

Figure 1651 ISP QoS Architecture

Customers may signal the precedence to become associated with packets from different sources via BGP communities. Specifically, communities 2 0, 2 1, and 2 2 signal precedence 0, 1, and 2, respectively. The bgp table-map command uses the bgp-qos route-map command to match these communities and set the precedence flag in the cEf table, as required route-map bgp-qos permit 10 match community 10 set ip precedence routine route-map bgp-qos permit 2 0 match community 11 set ip precedence priority...

Distributed Queue Dual

The standard resulting from this IEEE study is numbered 802.6, and named Distributed Queue Dual Bus (DQDB), which essentially describes both the topology used by the technology, and the media access mechanism. In this technology, illustrated by Figure 3-10, two optical fiber buses carry communications between all stations. The buses are unidirectional, and a DQDB station needs to attach to both, either through a passive or active fiber tap. One bus communicates with upstream stations, and the...

The Router LSA Link State Type

Every OSPF router sends this LSA, which defines the state and cost of the routers' links to the area. All the routers linked to a single area must be described in a single LSA the router LSA is flooded throughout only a single area. Examine the sample network shown in Figure 9-8. Figure 9-8. Sample Network Used to Explain Different LSA Types Figure 9-8. Sample Network Used to Explain Different LSA Types R1 and R2 are area routers connected to a single area only. They have connections to the...

Classful Distance Vector to Classless Distance Vector Protocol RIP to Enhanced IGRP

Migrating from RIP to Enhanced IGRP requires careful planning because there is a possibility of routing loops and because metric conversion must be considered. For example, in the network shown in Figure 12-2, the customer does not want to create hierarchy in the physical topology to accommodate OSPF. However, without hierarchy, OSPF cannot be implemented because of scaling issues. In this case, the only other option is Enhanced IGRP. As with any other routing protocol, Enhanced IGRP has...

Classless Interdomain Routing

As the popularity of the Internet has grown, it has become the global media for the transfer of information. However, as popularity increased, new problems continued to appear. Small organizations applied for IP addresses, but providing them all with a class A or class B address was not feasible. Instead, these organizations were assigned class C addresses, or, in a large number of cases, multiple class Cs. With such a large distribution of IP addresses, the routing table on the Internet began...

Link State Packets

Link-state packets are divided into two types level 1 and level 2. Level 2 packets contain information about all the reachable prefixes within the IS-IS domain. The topology for level 1 packets is known for the local area only, so these packets are included in the level 1 LSP. Individual LSPs are identified by four components of the LSP header. These include the LSP ID, the sequence number, the checksum, and the remaining lifetime. LSP ID is divided into the source ID, the PSN number, and the...

Nonrepeaters

Specifies the number of object instances in the variable bindings field that should be retrieved no more than once from the beginning of the request. This field is used when some of the instances are scalar objects with only one variable. The Get-Request message provides for retrieval of particular OIDs and is sent from the station to the agent on the router. The agent responds with a Get-Response message, which contains the value of the OID(s) requested. A Get-Next-Request is used to retrieve...

Evolution of the Internet

Socially, economically, culturally, and technologically, for many of us the Internet already has changed our lives dramatically. For many more of us, it soon will. Along with telephones, televisions, and automobiles, Internet connectivity is rapidly becoming a commodity in every home. Yet, as dramatic as the changes have been, it is worth remembering that initially, at least the Internet grew at a considerably slower pace than the telephone network (although some would argue that this is merely...

Requirements and Constraints

Before delving into the typical topologies, it is wise to understand the overall network design process. As with any systems design effort, network design is an exercise in meeting new and old requirements while working within certain constraints. These constraints include money, labor, technology, space, and time. In addition, there may be social or political constraints, such as the mandated use of certain standards or vendors. Economic constraints play a major role in any network design....

Basic IP Concepts

Internet Protocol (IP) routing is the heart of the Internet today. It is the only protocol that carries information between different domains. All other protocols (for example, Novell and AppleTalk) work locally within their own domains. Because IP is designed to send information packets from source to destination without understanding the underlying technologies, it does not guarantee delivery of the packet. It simply puts forth its best effort to send the packet to its destination. IP packets...

Description of the BGP4 Protocol

Note that this chapter limits its description of BGP to version 4, which is the one used almost exclusively on the Internet today. BGP4 has four message types OPEN messages are used to establish the BGP session. UPDATE messages are used to send routing prefixes, along with their associated BGP attributes (such as the AS-PATH). NOTIFICATION messages are sent whenever a protocol error is detected, after which the BGP session is closed. KEEPALIVE messages are exchanged whenever the keepalive...

BGP Neighbor Relationships

BGP neighbor relationships, often called peering, are usually manually configured into routers by the network administrator, according to certain rules and to logically follow the overall network topology. Each neighbor session runs over TCP (port 179) to ensure reliable delivery and incremental, rather than periodic, rebroadcasting of updates. These two characteristics distinguish BGP from the nature of most interior routing protocols. Incremental updates occur when all routing information is...

A RSVP Packet Header

Each message begins with a 4-bit RSVP version number the current version is 2. This is followed by a 4-bit flag field, which is currently unused. The type field indicates the message type A 16-bit standard TCP UDP checksum is used over the entire contents of the RSVP message. The checksum field is assumed to be zero. Length is the RSVP packet length in bytes. The Send TTL is matched to the TTL of the IP packet in which the RSVP message was encapsulated. Each RSVP object field begins with an...

Border Gateway Protocol

Earlier chapters in this book described interior routing protocols used predominantly for routing within autonomous systems. This chapter discusses the Border Gateway Protocol (BGP), which is predominantly used for routing between autonomous systems. The approach of this chapter is similar to the earlier chapters on routing protocols It begins with a bird's-eye view of how the protocol works and then dives straight into the details of its various messages, routing information, and states. Next,...

Classful Distance Vector to Link State Protocol

For the sake of this discussion, imagine you are migrating from IGRP, which is the classful distance-vector protocol, to a link-state protocol, OSPF. Remember that both OSPF and IS-IS require hierarchy. The network in Figure 12-2 shows that no hierarchy exists in the network in question, so you must change not only the network protocol, but also the physical circuit to accommodate the hierarchical structure. Figure 12-2. Non-Hierarchical Network Architecture Figure 12-2. Non-Hierarchical...

OSPF Over Different Physical Media

Classically, networks can be divided into three types broadcast (Ethernet, Token Ring, and FDDI), point-to-point (HDLC and PPP), and non-broadcast multiaccess (Frame Relay, SMDS, and X.25). Behavior of OSPF over broadcast and point-to-point networks is uncomplicated, but the behavior of OSPF over non-broadcast multiaccess networks (NBMA) requires further explanation. When configuring OSPF over NBMA networks, you can configure the router to behave in four ways Each of these methods is discussed...

Exchanging Protocols

With the introduction of classless routing, it was not possible for classful routing protocols such as RIP and IGRP to understand entire routing tables. In some cases, routing packets to destinations within the same major network is no longer possible. Therefore, it may become necessary to exchange one protocol for another. Take, for example, the case of the Internet making use of class A networks between multiple customers. As discussed in Chapter 6, Routing Information Protocol, RIPV1 will...

Inter Switch Link ISL

This is the Cisco proprietary protocol for connecting multiple switches and maintaining VLAN information as traffic travels between switches. It is a method of multiplexing bridge groups over a high-speed backbone. With ISL, an Ethernet frame is encapsulated with a header that transports the VLAN ID between switches and routers. This VLAN ID is added to the frame only if the frame is destined to a non-local interface. Examine Figure 16-4. If switch 1 receives traffic from segment A and wants to...

Access Routers

Access routers connect the customer or enterprise site to the distribution network. In the ISP case, the router at the remote end of an access link is typically the customer premises equipment, and may be owned and operated by the customer. For large enterprise networks, in which the LANs and WANs are managed by different divisions or contractors, the access router typically is managed by either the WAN or the LAN operator usually this is the latter if the LAN is very large. You now may wonder...

PIM Sparse Mode

The periodic broadcast of all multicast traffic to refresh the prune state clearly makes PIM dense mode unsuitable for very large networks. PIM sparse mode offers the best of both worlds. It uses shared-tree operation for low traffic flows, and has a mechanism to move to a source-based tree for high traffic flows. Unlike dense mode, sparse mode uses an explicit join model for receivers. The key to this transition is the notion of a rendezvous point (RP). Revisit the topology example that we...

Ciscos RIP implementation

Cisco RIPV2 support includes VLSM support, authentication, discontiguous network, multicasting, and next hop address support. RIP version 1 is not operable in today's classless environment. Because of its many limitations, it should be used only in moderately sized, fairly homogenous networks. With the advent of Classless Interdomain Routing (CIDR), protocols must implement classless behavior. As companies grow, so does the consumption of address space. Two issues have become clear to most...

Introduction to QoS

One school of thought believes that IP QoS is not cost-effective and that spending money on fiber, over-engineering, or very responsive capacity-upgrade mechanisms is more cost-effective. It seems wise to subscribe to that school of thought when considering the backbone of a network. Nevertheless, simply waving money around does not immediately increase global fiber infrastructure. Networks will always face short-term congestion and isolated hot spots within a network architecture, such as...

Weighted Random Early Detection

The queuing algorithms discussed so far are concerned with determining the behavior of the router in the presence of congestion. In other words, they are congestion-management algorithms. Each algorithm results in packet drops from the tail of a queue in the event of congestion. As you have already seen, this can result in TCP flow synchronization, associated oscillatory congestion, and poor use of network bandwidth. Moreover, in some cases, multiple packets from a single TCP session tend to...

The Update Message and BGP Attributes

The UPDATE message is used to transfer routing intelligence. Its format is shown in Figure 116. The UPDATE message may advertise routes, withdraw routes, or both. Unieasibte Routes Length octets) Total Path Attribute Length (2 octets) Network Layer Reachability Information variable) The UPDATE message begins with the withdrawn-routes length, which may be zero, in which case no routes are withdrawn. Otherwise, the withdrawn-routes length contains a number of < length,prefix> triples, with...

Figure 131 IGMP Operation

The message may be sent to the ALL-MULTICAST-HOSTS address (224.0.0.1) or to a specific group address, indicating that group-specific querier is desired. All routers listen for such messages, and the router with the lowest source IP address on the LAN is elected as the IGMP QUERIER for the LAN or for the specific group. After a querier is elected, it periodically sends IGMP MEMBERSHIP QUERIES for each active group to the ALL-MULTICAST-HOSTS address. Because multicast IP traffic is also sent to...

OSPF Interface Configuration Constants

OSPF has two types of constants Fixed constants These values have fixed architectural values and are not configurable. They include Link State Refresh Time, Min Link State Interval, Max Age, Link State Infinity, Default Destination, Initial Sequence Number, and Max Sequence Number. These values can be changed according to the requirements. Configurable constants include Interface Output Cost, Retransmit Interval (RxmtInterval), Interface Transmit Delay, Hello, Dead Interval, and Router...

Enhanced IGRP Metrics

Enhanced IGRP uses five metrics to determine the best path to a destination lowest bandwidth, total delay, reliability, load, and MTU Lowest bandwidth is calculated based on the minimum bandwidth to the destination network. Total delay is the sum of all the delays to the destination network. Reliability refers to how much the information can be trusted or how reliable the path is. This is not activated, by default. Load refers to how congested the outgoing link is fully loaded is considered...

Multicast Routing Protocols

Multicast differs from simple broadcast in the sense that it only attempts to deliver a packet to interested users. It differs from unicast or pointcast in that only one copy of a packet travels over any link. For large-scale applications, this can represent a huge reduction in the use of bandwidth and switching capacity. The characteristics of multicast routing are well suited to conferencing applications, but these are by no means the only applications. Multicast can also enable auto-resource...

OSPF Packet Format

OSPF is a routing protocol designed specifically for the TCP IP environment, and it runs directly on top of IP protocol 89. Another noteworthy point about OSPF is that it does not perform fragmentation and reassembly these functions are performed at the IP layer. Every OSPF packet shares a common 24-byte protocol header, as shown in Figure 9-1. Routing protocol packets are sent with a type of service of zero. Figure 9-1. The 24-byte Common OSPF Header Shared by All Protocol Packets Figure 9-1....

OSPF Packet Types

As mentioned previously, OSPF has five kinds of routing protocol packets, and each is identified by the Type field in the protocol header. Now, we will discuss those packet types in more detail. OSPF Packet type 1, as shown in Figure 9-2, is the hello packet. Hello packets are sent periodically to all functional OSPF interfaces, and are used to detect neighbors. OSPF packets are sent to the multicast address 224.0.0.5. The basic function of the hello packet is to establish a neighbor...

Figure 111 Comparison of Apple Talk and the OSI Model

AppleTalk Dala Stream Protocol (ADSP) EthetT lk Link Accass Protocol ( LAP) Local Talk Link Access Proloool (LLAP) Token Talk Unk Access Protocol TLAPj FDDITalk Link Access ProlocoL (FLAP) Token Ring' IEEE S02.5 Ha ndw& re One useful feature of AppleTalk, for small networks at least, is its capability of grouping users and resources into networking communities via the Zone Information Protocol (ZIP). No real notion of this feature exists in the TCP IP suite the function is left to...

The OPEN Message and Capability Negotiation

The OPEN message is shown in Figure 11-4. 01234567 8 901 2345673901234567890 1 This message begins with a one-byte BGP version number this is generally version four, although Cisco routers will negotiate between versions 2 and 4 unless you explicitly set the neighbor ip-address peer-group-name version value. In almost all cases, you use version 4. A two-byte ASN contains the AS of the remote neighbor. If this does not correspond to the ASN listed in the neighbor ip-address peer-group-name...

Prefix variable

It is important to note that an update containing previously-announced NLRI implicitly withdraws the early advertisements. Therefore, when updating the attributes for a particular NLRI, such as changing MED, it is not necessary to send an explicit withdraw for the NLRI in advance. The NOTIFICATION Message and BGP Errors Notification messages are sent in response to a BGP error condition. These include protocol errors such as malformed updates, confusion in the BGP state machine, or even...

BGPs Finite State Machine

The finite-state machine associated with BGP is shown in Figure 11-15. Figure 11-15. BGP's Finite State Machine Figure 11-15. BGP's Finite State Machine Other BGP literature describes states 1 through 6 only. States -1 (prefix exceeded) and 0 (administrative shutdown) are specific to the Cisco implementation. To avoid confusion with state numbers used in other literature, in this book these Cisco specific states are numbered -1 and 0, respectively. Eight possible states exist in BGP's...

What Is Covered in This Book

The material in this book is separated into two parts Part I Chapters 1 through 5 covers general aspects of network design, WAN, LAN, and router technologies. Part II Chapters 6 through 16 discusses the deployment of routing protocols, QoS issues, and network management Chapter 1, Evolution of Data Networks, describes the evolution of the world's largest IP network the Internet. You will discover what lessons have been learned in scaling the Internet from just a few users to hundreds of...

Caching Technique Case Study

In previous sections about Cisco switching techniques, we discussed how fast switching is performed, how cache is created from the routing table, and what information is kept in cache. You might be wondering how the cache is populated. During the case study, the text discusses what happens when a packet that must be fast-switched reaches the router. The cache is built from the routing table. In the scheme prior to CEF, the routing table is built when the routing protocol injects routes. Before...

Novell Net Ware

It is debatable whether OSI or IPX represented the most serious contender to TCP IP as the ubiquitous networking technology of the future. At one time, IPX enjoyed an installed base that far exceeded IP, and numerous plans arose to build the IPX equivalent of the Internet. Novell NetWare (see Figure 1-12) is based upon a client-server paradigm, with the initial intent of sharing large disk volumes among a set of relatively meagerly equipped clients. As with AppleTalk, Novell NetWare employs a...

Enhanced IGRP and Variance

Enhanced IGRP can simultaneously use unequal cost paths to the same destination, which indicates that traffic can be distributed among multiple (up to four, by default) unequal cost paths to provide greater overall throughput and reliability. An alternate path is used if the variance condition is met. The variance condition depends on two factors The local metric must be greater than the metric of the next router, so the next hop router must be closer to the destination than the local best...

TfpX D4 10140

Figure 8-16 shows that the D1 router does not readvertise the route to itself, which assists in preventing routing loops. By default, split horizon is enabled on all LAN and point-to-point interfaces, but it is disabled on all NBMA networks for all distance-vector protocols, including Enhanced IGRP. In certain non- meshed NBMA networks, it becomes necessary to deactivate split horizon because in hub- and spoke-type setups, the hub router receives a route from all remote routers. It will not...

Capacity Planning

Link utilization is one of the mainstays of performance management. The ifInOctets and ifOutOctets objects (or ifHCInOctets and ifHCOutOctets for high-speed interfaces offering 64-bit counters) are a critical way to predict congestion and the need for bandwidth upgrades or routing optimizations. Once again, the polling period used can have a dramatic impact on the perceived utilization of the link. Packet transmission tends to be choppy (indeed, if you think about it, a link either is carrying...

The World Wide

In 1991, WAIS, Gopher, and the World Wide Web were released as a means to seek out and follow information on the Internet in a far more intuitive and accessible way than the previous directory searchArchie tools. The evolution of the World Wide Web and the emergence of the Web browser as the dominant Internet application increased the overall attraction and accessibility of the Internet to the public. In addition, it induced rapid growth in traffic levels that continue to be a challenge to...

Bootstrap Routers and Candidate RPs

BSRs and RPs are a critical part of the scalability of PIM V2. This section discusses the process of BSR election and RP determination in more detail. This discussion is included for completeness however, it is recommended that you use auto-RP instead of BSR. You will learn about auto-RP in the next section. A large sparse mode network should have multiple candidate RPs, which should be placed in the backbone. Candidate RPs are configured via the ip pim rp-candidate global configuration...

NSFNETT3 and ENSS Routers

By the end of 1993, traffic on the NSFNET backbone had increased to the point of requiring 45 MB (T3) connections. Although the ARPANET had been decommissioned for three years by then, increased NSFNET connectivity more than compensated for this fact, through growth in the regionals and by the peer networks operated by the remainder of theBig Four the Department of Energy, the Department of Defense, and NASA. NSFNET also encouraged academic and research usage through itsConnections program (see...

Choosing between IBGP and EBGP

Both IBGP and EBGP can be used for the purpose of peering between regions. Without any extensive policies between regions, and if a default route will be sent from each IBGP router into each region, you would have to use the registered AS number for the IBGP core. You need the registered AS number in the Internet connection because the core would send a default route into the regions. Also, the default route should originate only from the core. Because the core is all-knowing, it should...

Review Questions

1 When you see a cache ager running on a network, should you be alarmed 2 Why do you see so many 32 entries on a network, and what can you do to prevent these 4 How do you enable optimum switching 5 In what situation is it wise to disable fast switching 7 Will cache ager run with FIB 8 If CEF does not process-switch, how does it receive the MAC-layer information 10 Does FIB support load sharing 11 Does CEF support access lists 1 When you see a cache ager running on a network, should you be...

Figure 810 Oversubscribed Hub and Spoke

The spoke site has a speed of 56 Kbps and is configured at 25 Kbps to accommodate the second Enhanced IGRP rule. This would affect the convergence of Enhanced IGRP because the data traffic is fairly low. This means that you can allow Enhanced IGRP to use 90 percent of the configured bandwidth. Figure 8-10 shows that the hub site has 256 Kbps, and each of the 10 remote VCs has an actual bandwidth of 56 Kbps. Therefore, adding all the VCs shows that more bandwidth exists at the remote VCs than at...

Summary Link State Types 3 and

Summary type 3 propagates information about a network outside its own area. Many network administrators assume that summary LSA generates information outside the area by summarizing routes at the natural network boundary, although this has been proven untrue. For example, a summary LSA will not summarize all subnets of a major network 131.108.0.0 in a 16 route. Summary in OSPF does not mean that summarize occurs at the classful network boundary. In this case, summary means that the topology of...

Circuit Switching Links Synchronous Optical Network

Synchronous Optical Network (SONET) was defined in the 1980s as a standard by which carriers could build multivendor transport infrastructure. SONET is divided into three areas Physical, Payload, and DCC. SONET uses a frame structure that repeats itself every 125 ms, enables providers to set up a hub topology rather than just point-to-point connections, and supports a fiber optic ring, which is created by fiber optics. In case of a failure, a bidirectional ring can be used, which is capable of...

Managing Routing Policy

Even if a routing update is authenticated, a configuration error in a customer or peer's network could cause them to send you invalid routes. A classic and disastrous example is the dual-homed ISP customer who does not filter BGP routes and offers transit for the entire Internet to their upstream ISP. Ingress route filtering is the responsibility of the customer and the network service provider. However, the onus is really on the provider, who will generally be blamed by the Internet community...

External LSA Link State Type

External LSA describes destinations outside the OSPF domain. A route received via another routing protocol and redistributed into OSPF is considered external to OSPF. Any destination that is not originated by the local OSPF process is also considered external. Refer to Figure 9-14. Router R7 redistributes 140.10.0.0 into OSPF 140.10.0.0 was not originated by the local OSPF process. In Figure 9-17, R7's link-state ID field is set to the external destination advertised (140.10.0.0), and the...

Building an IBGP Core

In Figure 16-14, USA.Cal.R1 needs full IBGP mesh, so it must maintain peering statements for all the IBGP-speaking routers. However, full IBGP mesh causes difficulty with optimal routing. To accommodate optimal routing and add predictability, Alpha.com is not peering USA.Cal.R1 with Euro.Fra.R2, which accommodates the physical topology. To accommodate optimal routing with IBGP, Alpha.com must break the IBGP model and perform many tricks that complicate the network. Another possible problem...

Configuration Example

In this example, the access router has ten static customers. Of those ten customers, you do not want to send eight routes to external BGP neighbors, but you do want to send two routes to the external neighbors. The first eight static routes should not be exported, and the last two should be sent to the external peers. The static routes on A1 are the following The following would be the BGP configuration of the A1 router ip bgp-community new-format router bgp 109 neighbor 131.108.10.1 remote-as...

Distribution Regional Network Design

The role of the regional network is to route intra- and inter-regional traffic. The regional network generally is comprised of a DC as the hub and a number of access POPs as the spokes. Usually, two redundant routers in each regional network will connect to the backbone. DCs may also provide services such as Web-caching, DNS, network management, and e-mail hosting. In some cases, the latter functionality may be extended into major POPs. Placement of DCs is generally an economical choice based...

Cache and Recursive Lookup

You can see from the previous discussion that, although this technique is efficient, it has drawbacks, such as scalability problems. These problems do not affect the enterprise customer because the networks are not changed rapidly and frequently, and because they do not carry very large routing tables. Demand caching is a scalable method for the enterprise environment because packet flow is not very dynamic. Cache deletion frees space in the memory as well. ISPs, on the other hand, see the...

RIPV2 and Discontiguous Networks

By default in Cisco, RIP version 2 supports automatic route summarization. This causes the route to be summarized as a classful boundary when crossing a major network. This affects discontiguous networks, as shown in Figure 7-4. Figure 7-4. RIPV2 and Discontiguous Networks Figure 7-4. RIPV2 and Discontiguous Networks In Figure 7-4, R1 and R2 have their Ethernet interfaces connected to Network 131.108.0.0. The serial interface between the two routers is a different major network in this case,...

Packet Switching Links Frame Relay

Frame Relay was initially developed by the American National Standards Institute (ANSI) in 1984. Cisco Systems undertook major redevelopment of Frame Relay in 1990. StrataCom (now part of Cisco Systems), Northern Telecom, and Digital Equipment Corporation formed a consortium to focus on the development of Frame Relay technology. This consortium developed some additional features for the internetworking environment. Frame Relay is a packet-switching technology that provides a connection between...

The Broadcast Model

The broadcast model requires the selection of a designated router, as well as a backup designated router. In addition, all the routers in the cloud must be fully meshed. For some organizations, this can be expensive and impractical. If the mesh breaks, a hole is created. In Figure 16-11, for example, assume that USA.Cal.R1 becomes the designated router and that USA.Arz.R3 is elected as the backup designated router. All the routers should have a connection to the designated router. If USA.Tex.R6...

Multicast Configuration

The multicast architecture for the SFO region is shown in Figure 16-51. Where supported, multicast distributed switching is enabled. Otherwise, non-distributed routing is enabled. For simplicity, ip pim-sparse-dense-mode is enabled on all interfaces with the network, and on customer interfaces as requested by the customer. That is, if the customer wants multicast service, ip pim sparse-dense mode is enabled on the interface leading to that customer. Every backbone router is configured as both...

Drawbacks of OSI

OSI standards tended to be overly rigid, however, with respect to layering. In addition, they were cumbersome and slow because of the need to support all contingencies, and the standards were developed slowly because consensus was hard to reach. The success of OSI played upon customer and government fears of depending on a single vendor, yet, with a few exceptions, failed to encourage useful implementations. The standards were written in the style of legalese, which made them difficult to read...

Design and Configuration Case Studies

Designing a successful IP network is one of the essential elements surrounding modern internetworking. A poorly designed network affects the performance of the routers, as well as the entire network. As networks become an essential part of any successful business, scaling and faster convergence also play a major role. This chapter presents the process of designing large networks. Specifically, it addresses a network design first, with respect to the enterprises then, with respect to the ISPs....

Using the nonexitmap Command

The second method is for Beta.com to use a Cisco feature introduced in the 11.1 CC release. This non-exit-map command is used with advertise-map. The configuration of one of the peering routers of Beta.com that connects with Alpha.com would be the following router bgp 8 network 198.10.1.0 network 198.10.2.0 network 198.10.3.0 neighbor 131.108.1.2 remote-as 109 neighbor 131.108.1.2 route-map test1 out neighbor 131.108.1.2 advertise-map test3 non-exist-map test2 access-list 1 permit 198.10.1.0...

Figure 128 Typical ISP Setup with Static and BGP Customers

Figure 12-8 shows that the static customers are connected to the distribution routers or access routers. The distribution routers will always run BGP and, most of the time, will have BGP customers connected to them. In some cases, ISPs do not run BGP on the access routers if they have only static customers connected to them. Figure 12-8 shows that the static customers are connected to the distribution routers or access routers. The distribution routers will always run BGP and, most of the time,...

Switching with QoS

Traditionally, queuing of packets within IP routers has been first-in, first-out (FIFO). More recently, Layer 3 quality of service features have been introduced to enable large-scale IP networks to effectively handle a mix of best-effort, and mission-critical or time-sensitive applications. This is typically achieved through congestion management and control algorithms implemented in a packet scheduler associated with the outgoing interface. The scheduler may perform a number of functions...

Figure 135 IGMPV3 Message Format

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 901 All routers begin by sending queries for multicast-enabled interfaces. However, in IGMPV2 V3, routers will suppress queries on LAN interfaces for a few seconds if they hear a query from another router on the LAN with a lower source IP address. The following message also has the format shown in Figure 13-4. A host sends this packet in response to an IGMPV1 MEMBERSHIP QUERY from the querying router. The group address contains the group...

Overview of Communications History

Networks are now a core component of our business and personal lives. Today, businesses that may hobble along with the loss of telephone service can be rendered nonfunctional by the loss of their data network infrastructure. Understandably, corporations spend a great deal of time and money nursing this critical resource. How and why did this dependency occur Simply because networks provide a means to amplify all the historical communication mechanisms. Nearly 50,000 years of speech, at least...

Figure 1623 Asymmetric Routing for Betacom

This setup, which is complicated, is shown in Figure 16-22. The routes advertised by Beta.com to Alpha.com are individual class C routes owned by Beta.com. Beta.com also advertises the same three class C networks to ISP3, which owns this CIDR block. ISP3 summarizes this block to the Internet backbone. As shown in Figure 16-22, routes from ISP1 and ISP2 are more specific for Beta.com class networks than the one advertised by ISP3. This causes asymmetric routing because all routers in Beta.com...

Introduction to the Distance Vector Protocol

In a distance-vector protocol, each router or host that participates in the routing protocol maintains information about all other destinations within the autonomous system. This does not indicate that each router knows which router originated the information, as in link state, but each router is aware of the neighbor that will be used to reach that destination. Each entry in the routing table includes the next hop, to which the datagram should be sent on its route to the destination. Each...

Domain Name Service

Having a well-chosen naming plan for all routers and intelligent in-addr, ARPA (reverse) lookups for router interface addresses can ease fault management considerably. Read the following traceroute output 1 171.69.213.161 AS 75 0 msec 0 msec 4 msec 2 sj-eng-lab1.cisco.com (171.69.9.1) AS 75 4 msec 4 msec 4 msec 3 sj-eng-corp2.cisco.com (171.69.4.143) AS 75 4 msec 0 msec 0 msec 4 sj-wall-1.cisco.com (198.92.1.137) AS 109 4 msec 4 msec 4 msec 5 barrnet-gw.cisco.com (192.31.7.37) AS 109 4 msec 4...

Avoiding Routing Loops

Ensure that the area range configured on the ABR is a route to null interfaces, or you will risk a routing loop. Figure 16-10 shows a typical situation in which a routing loop could be created. Figure 16-10. Routing Loop Caused by Summarization Figure 16-10. Routing Loop Caused by Summarization In Figure 16-10, the ABR sends a route for subnets 172.16.0.0 to 172.16.15.0, and the ASBR sends the default route. ABR loses its route to one of the subnets if, for example, subnet 172.16.12.0 24 has...