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...

A3

On router D3, a point-to-point subinterface is configured so that the cost is set according to the PVC interface Serial4 1 no ip address encapsulation frame-relay cdp enable interface Serial4 1.1 point-to-point ip address 10.1.3.126 255.255.255.252 ip ospf cost 390 (for 256K PVC) frame-relay interface-dlci 199 interface Serial4 1.2 point-to-point ip address 10.1.3.130 255.255.255.252 ip ospf cost 1785 (56k PVC) frame-relay interface-dlci 198 interface Serial4 1.3 point-to-point ip address...

Aaa accounting

Tells the router how and when to report access information to an accounting server. Try using tacacs+ to account for the start and stop of all exec sessions, and to track all configuration commands. A more suitable route access control configuration is this one service password-encryption aaa new-model login default tacacs+ enable login console none enable tacacs+ enable aaa authentication aaa authentication aaa authentication commands 15 default start-stop tacacs+ enable secret 5 3242352255 no...

Abr

The routers are sending different type 7 routes, but first the router R1 is redistributing static in configuration. This is used to summarize the single-attached routers. Routers with singleattachment to R1 would be learned vi a RIP. R1 will not redistribute any of the RIP-learned routes into OSPF. R1 will only redistribute the static null route into OSPF. This way, a single PVC flap does not cause flooding of external link states. Only those RIP routes that are coming from dual-attached sites...

Access Design

In most cases, an access router serves a large number of customers. With modern access technology, this number can reach the thousands. As a result, resilient connectivity to the distribution routers is recommended. This may be accomplished using a self-healing LAN technology, such as FDDI. Alternatively, as with the connectivity between distribution and backbone routes, this may involve the use of redundant LAN switches. If the access router is the only node in a small POP, redundant WAN...

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...

Address Plan

IP address blocks are assigned to regional networks in 16.x 16 (a class B size) chunks. Within each regional network, the first 10 class C's in each block are reserved for infrastructure the remainder are allocated for use by customers. SFO has block 16.0 16, and LAX has 16.1 16. For IS-IS NET address allocation, ISPnet uses the format 00.000L.macaddress.00, where L is the highest IS-IS level interface of the router (1 or 2), and macaddress is the MAC address of the first LAN interface on the...

Advertising Router

When the router detects a missing piece of the database, it will send the database request packet. In this request, the router indicates to the LSA what it hopes to find. The LSA is indicated by link type, link ID, and advertising router. When the router receives a response, it truncates the LSA from the request and then sends another request for the unsatisfied LSAs. This retransmission of unsatisfied LSAs occurs during every retransmission interval. The retransmission interval is a...

Apple Talk

The AppleTalk protocol was introduced in 1985, with further refinements in scalability and media support in 1989. Following the plug-and-play ideal of the Apple Macintosh computer, small AppleTalk networks required literally no configuration to share resources such as printers and disks. AppleTalk maps fairly well to the OSI model of network protocol layering (see Figure 1-11). In addition to offering support for multiple physical media and link-level protocols, AppleTalk contained a datagram...

Are Customers

In Figure 14-10, AS2 is the service provider, and AS1 and AS3 are customers. If access router A1 in AS2 receives traffic from AS1 that is destined for AS3, and classifies packets based on BGP information associated with the source address, the route is successful because A1 receives BGP updates directly from AS1, containing the necessary classification data. Consider, however, that AS3 wants all packets that it is destined to receive to be allocated a certain IP precedence within AS2's network....

Area Setup of OSPF

The area setup of OSPF is shown in Figure 16-45. The physical setup differs from the one in Enhanced IGRP because it is dependant on the location of the link between one region hub router and the other regional core router it could be the local area or area 0. For example, MKS can insert a link between a hub router in area 2 with a regional core router in area 1. If the link is in area 1, all the traffic from area 2 destined to area 1 would begin to travel on this link, which is only for...

Assert

The ASSERT MESSAGE, shown in Figure 13-14, is used in both dense and sparse modes. PIM routers maintain an outgoing interface list for all multicast group addresses. If an interface is in the outgoing list for group X, the router multicasts the packets it receives for group X to all interfaces in the list. Therefore, under loop-free conditions, the router would not expect to receive any packets for group X on any interface in X's outgoing interface list. If it does, the router generates an...

Authenticating Routing Updates

Ensuring the integrity of the dynamic routing fabric within a network is one of the most critical network-management functions. Bogus routing updates, whether malicious or accidental, can severely disrupt network operations or even render the network completely useless. Cisco routing protocols have two forms of authentication plain text or MD5. Obviously, the latter is preferred, if supported for the routing protocol in question. Plain-text authentication is barely better than none at all. As...

Automated Fault Resolution

After a problem has been isolated, the NMS has the opportunity to perform automated rectification. However, it is rare to see such systems in practice. In most large networks today, automated fault resolution or, in other words, work arounds are performed by the fail-over mechanisms of dynamic IP routing protocols or by link-level fail-over mechanisms, such as those available in SONET and FDDI. Configuration and Security Management Configuration management involves maintaining a database that...

Automated Polling and GUIs

Polling of network devices offers a very reliable way to detect problems. However, there is a trade-off between the speed with which you want to detect problems and the bandwidth and CPU consumed by the polling process. The ubiquitous Internet Control Management Protocol (ICMP) ping, which is a mandatory part of the IP stack on all devices, is an often overused way to accomplish system monitoring. This is because ping does not indicate the operational status of the device it simply indicates...

Autonomous Switching

One advantage of the single CPU architecture is that performance improvements could be obtained merely by increasing the speed of the CPU (which occurred through the CSC and CSC3 motherboards, respectively). However, as the demand for greater throughput increased, it became necessary to increase the bus speed and offload some of the switching from the CPU. A new series of bit-slice-processor interface cards, coupled with a 533 Mbps cbus and associated controller, did just that. In effect, the...

AutoRP

The mechanisms of BSR and candidate RPs are quite complicated. Cisco offers an elegant and simple alternative called auto-RP. To enable auto-RP, configure all RP routers to advertise active groups via the ip pim send-rp-announce global configuration command, as follows ip pim send-rp-announce loopback 1 scope 16 These announcements are sent to the well-known group address CISCO-RP-ANNOUNCE (224.0.1.39). Loopback 1 is an RP address advertised in the announcements. You should configure it to be...

Auto Summary Enhanced IGRP Summarization and Query Scoping

Query propagation occurs when an Enhanced IGRP router loses a route to a destination, and therefore goes into an active state. During this process, the router queries all its neighbors for the lost destination. Query propagation stops one hop from the point of summarization and auto-summary. This is a definite advantage if all the routes were sent across to all the routers in the network, a remote node in one part of the network would send a query for a lost route to the other end of the...

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...

Backbone Core Network Design

In early data networking, the topology for the network backbone was relatively simple Operations were centralized, so a star topology made the most sense and, in some cases, this was the only topology the technology would support. This did cause the center of the star to become a single point of failure, but because no real traffic flows existed between spokes on the star, this was not a major cause for concern. With the move toward multiple client-server and peer-to-peer relationships, the...

Backbone Routers

The backbone routers core1.sfo and core2.sfo reside in the San Francisco DC and are responsible for connecting the regional network to the backbone. These routers forward packets to and from the region. They also advertise reachability for that region, either to the core routers of other regions (in other major cities), or to external peer networks (other ISPs). Backbone routers are also peers in terms of the useful reachability information they possess. This does not imply that router...

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...

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...

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...

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...

BGP Policy Propagation

CAR and WRED provide QoS policy enforcement within the router, but how is this policy propagated throughout the network BGP policy propagation makes this possible by enabling you to adjust the IP precedence of a packet based on its source or destination address and, optionally, based on the associated BGP community and or as-path. Recall from Chapter 11, Border Gateway Protocol, that an as-path is a mandatory BGP attribute that lists each autonomous system through which the route has passed. As...

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...

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...

Boundary

Router D1 in Figure 8-12 would redistribute the routes. Notice that the interface between D1 and D2 has an IP address of 10.10.1.0. This indicates that if you had the same Enhanced IGRP process running across the entire network, with the default behavior of auto-summary activated, all the subnets of the 131.108.0.0 network would have been advertised as 131.108.0.0 16 routing entry, which is the major network class B. Now, assume that in the network shown in Figure 8-12, there are different...

Building an EBGP Core

Now, assume that Alpha.com changes the model to the one shown in Figure 16-16. Instead of an IBGP core, Alpha.com is building an EBGP core. With this new model, the company does not have to fully mesh all the regions because it wants to implement EBGP. Alpha.com also does not have to worry about race conditions, it can maintain policies, and it can perform optimal routing without fear of having to adjust administrative distances. Alpha.com can fully mesh all the routers in the core running IBGP...

Building the Backbone Topology

Because you have a basic need for resilience in the backbone, a good starting point for the backbone topology is a ring connecting all distribution networks. This ring could represent the minimum cost of WAN circuits, compromised by an initial estimate of major traffic flows, and possibly some very particular delay requirements (although this is rare, with notable exceptions being high-performance networks). Next, existing links can be fattened, or direct connections between backbone routers...

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...

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...

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...

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...

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,...

Migration Techniques

This chapter introduces techniques for migrating networks from one routing protocol to another. We also explain methods for scaling the protocol that you may be currently using by repairing damaged architectures. Most network problems are not related to protocols instead, they are related to poor planning and failing to anticipate network growth. This chapter discusses the possible reasons for migrations, and introduces techniques to ensure problem-free classless protocols. We also provide...

Quality of Service Features

After completing your study of routing protocols, you now can learn how to provide differentiated levels of service within the network. Routing and differentiated service can be intimately linked indeed, some routing protocols provide mechanisms for making different routing decisions based on the desired quality of service (QoS). However, for improved scalability, it is usually better to decouple routing and QoS in large networks. This chapter covers the following issues in relation to quality...

Network Operations and Management

This chapter examines the general network-management task, and provides some specific recommendations for sustaining and evolving large networks. The discussion centers around the five functional areas of network management originally defined by the International Standards Organization (ISO) fault, configuration, security, accounting, and performance. Some of this information is specific to the Cisco IOS, although many of the ideas are generally applicable to any large network. The approach is...

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....

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...

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...

Circuit Switched Networks

Packet-switched networks fundamentally differ from circuit-switched networks. As shown in Figure 3-2, a connection must first be established between two end hosts in order for them to communicate in a circuit-switched network. This can be achieved by i n-band signaling (call_setup) within a circuit in other words, the end host transmits a set of signals that allows the circuit to be extended, hop-by-hop, through the network. Alternatively, as in the case of the Integrated Services Digital...

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...

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...

Cisco Express Forwarding

Operational experience proves that the demand-cache mechanisms described previously did not scale well in highly dynamic routing environments such as the Internet. Fast-switching caches must generally be invalidated when there is a change in the routing table. Although route holddown can prevent cyclic churn, rebuilding the cache is computationally expensive because packets that initiate cache entries must be process-switched. CEF resolves this problem by building and maintaining a forwarding...

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...

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...

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...

Confederations

The idea behind a confederation is that the AS is broken into a number of sub-ASs. The sub-AS numbers are usually private AS numbers and are visible only within the confederation. To external EBGP peers, a confederation of sub-ASs still appears as a single AS. A confederation divides an AS into a number of smaller ASs that communicate using EBGP. In BGP sessions with networks outside the BGP confederation, the AS numbers used within the confederation are replaced with the confederation's...

Configuration Data

Collecting information for the network may seem like a chore, but it is absolutely necessary. Do not rely on auto-discovery mechanisms associated with many commercial NMSs. These may work for LANs or very small WANs, but they are totally unsuitable for very large networks. Only good planning and a meticulous process will produce a scalable result. The data stored in the configuration management database need not necessarily be router configuration data it may include, for example, contact...

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...

Configuring Router USACalR1

The configuration for Router USA.Cal.R1 would be as follows ip address 172.16.10.1 255.255.255.255 interface fastethernet 2 1.1 ip address 172.16.1.1 255.255.255.0 encap isl 100 interface fastethernet 2 1.2 ip address 172.16.2.1 255.255.255.0 encap isl 200 interface fastethernet 2 1.3 ip address 172.16.3.1 255.255.255.0 encap isl 300 interface fastethernet 2 1.4 ip address 172.16.4.1 255.255.255.0 encap isl 400 interface fastethernet 2 1.5 ip address 172.16.5.1 255.255.255.0 encap isl 500...

Congestion Avoidance Algorithms

Because the queue's tail drops, even in managed queue environments, and because it can induce global synchronization, there is a great deal of merit in environments that do not allow congestion in the first place. Covered here are two ways to accomplish this. The first is a combination of three features CAR, Weighted Random Early Detection (WRED), and BGP policy propagation the second is RSVP, a fully integrated bandwidth-management feature. Although CAR and WRED are stateless policy...

Congestion Management Algorithms

Congestion-management techniques are reactive, which means they determine how the network behaves when congestion is present. Unless they are configured by default within IOS, such as selective packet discard or FIFO, it is not wise to deploy these algorithms on a large scale. Instead, try using the congestion-avoidance techniques described later in this chapter. Despite their limited scalability, user-configured congestion-management algorithms can be useful in isolated instances, such as a...

Connections

Beta.com does not want Alpha.com to advertise its networks to ISP1 and ISP2, as long as Beta.com has a working connection to ISP3. In the event of failure, Beta.com wants Alpha.com to advertise its routes to ISPs. Alpha.com will run successfully because the company is leaking subnet routes to Beta.com for optimal routing with a community, and is asking it not to export subnet routes. Alpha.com would send 172.16.0.0 16 to Beta.com to leak this route to its ISP and would ask its ISP to set up a...

Conventions Used in This Book

Most chapters conclude with a case study, a set of review questions, and a selection of material for further reading. The case studies reinforce the major ideas in the chapter the review questions test your understanding and, in some cases, set the stage for further reading. A number of Cisco IOS configuration commands are discussed, but only the command options relevant to the discussion are described. Hence, the command options are usually a subset of those described in the Cisco IOS Command...

Copyright Information

Cisco Press logo is a trademark of Cisco Systems, Inc. All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without written permission from the publisher, except for the inclusion of brief quotations in a review. Printed in the United States of America 1 2 3 4 5 6 7 8 9 0 Library of Congress Cataloging-in-Publication Number 98-86516...

Core Dumps

If a router crashes, you may configure it to send a core dump to a server host. This can assist Cisco engineers in tracking down the cause of the crash. Core dumps can be delivered to a server via tftp (up to a maximum router memory size of 16MB), RCP, or FTP. Try using FTP It is easy to use, it works for all memory sizes, and server software is available for most platforms. Configuring the router to source the FTP session from the address of loopback0 to host cs-nms using a username of...

Creating a Loopback Interface

It is a good practice to create a loopback interface on Cisco routers running OSPF, most importantly, to create a router ID. In Cisco implementation, a loopback is taken as the router ID of the box. If a loopback interface is not configured, the highest IP address is selected as the router ID. Creating the loopback as the router ID provides stability. The loopback is a virtual interface on the Cisco router that will continue to operate well, as long as the router stays up. When the router ID is...

Custom Queuing

Custom queuing, also called class-based queuing (CBQ), allows a guaranteed rate or latency to be provided to traffic identified by a queue list. Queue lists are used to allocate traffic into one of up to 16 custom queues. Queues 1 through 16 are serviced sequentially, allowing a configurable byte count to be transmitted before servicing the next queue. Packets are not fragmented if they fall across the byte-count boundary servicing simply moves to the next queue when the byte count is exceeded....

Defining IP Addresses and Summarization

You should configure all the addresses within a campus to be out of a contiguous range for summarization at the router. In addition, you should leave open certain addresses for a range for future use. In this case, the address assigned for the VLANs ranges from 1 to 5. You could leave subnets 6 through 31 open for future use within the region, if you anticipate that the region will experience enough growth. In this case, it is expected that the region will grow, so a large portion of address...

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...

Deploying QoS in Large Networks

As usual, the approach is to perform computational expensive functions at the perimeter of the network, liberating the core and distribution networks to focus on aggregation and forwarding functions. Hence, it is recommended that you deploy policy control functions on the network perimeter and incorporate congestion avoidance, in the form of WRED, at the core. If traffic-shaping and or rate-limiting is required at the network perimeter, CAR represents the most flexible solution. This is not to...

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...

Dialer Profile Drawbacks

There are some points for concern with dialer profiles, however. Preconfiguration of the dialer profiles places each one within the respective area to which the backed area belongs. This causes the following problems Extra LSAs are generated one for each dialer profile. Each dialer profile introduces one additional route into that area, which may be undesirable, especially if you are summarizing. Any change in the LSA database (link flap anywhere in the network) will generate an ISDN call....

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...

Distributed Switching

With the introduction of the Versatile Interface Processor (VIP) cards, Cisco made the ultimate step toward a peer multiprocessor architecture. Each VIP card contains its own MIPS r4600 RISC processor, runs a mini-IOS kernel, and has configurable levels of SRAM and DRAM. Although the VIP1 was available for a short time, most of the installed base consists of VIP2s. The distributed features are targeted at the 7500 series (see Figure 5-6), but a VIP1 without distributed features is supported in...

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...

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...

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...

DUAL Message Types

DUAL messages are sent in one of three message types queries, updates, and replies. Queries are sent when a destination becomes unreachable. Updates are sent to indicate a change of metric to advertise a new destination. Replies are sent in response to the queries from a neighbor. If a query is received when no feasible successor is found, the query is propagated. If a feasible successor is found, the query is not propagated, and a reply is sent to the neighbor. Conditions for sending queries...

Enable Enhanced IGRP

Enhanced IGRP is enabled on a per-network basis. Eventually, it will be enabled on a per-subnet basis. Enhanced IGRP begins sending hello on all the interfaces in the specified networks. If a network is not specified under the Enhanced IGRP process, Enhanced IGRP will not send packets, nor will it include that network in Enhanced IGRP updates. In Figure 8-7, to enable Enhanced IGRP for network 10.0.0.0 but not for 131.108.0.0, the configuration would be as follows Figure 8-7. Enable Enhanced...

Enabling and Running Ciscos RIPV2

By default, the Cisco router will send and receive both version 1 and version 2 RIP packets, depending upon the neighboring router. To configure the router to process a specific version, you must use the following command At some point, parts of a network may be running legacy RIP version 1 while in the process of migrating to RIP version 2. You can configure certain interfaces to send and receive version 1 routes, and configure other interfaces to receive version 2 routes. This is illustrated...

Encoded Pruned Source Addressn

The Encoded-Unicast-Upstream Neighbor Address is the IP address of the upstream (RPF) neighbor that performs the join or prune. Holdtime instructs the recipient how long, in seconds, to maintain the requested join prune states. Oxffff is used to signify forever, and 0 is used to signify immediate timeout of the state. Number of groups indicates the number of multicast group sets in the message. Each set consists of an Encoded Multicast Group Address, followed by a list of encoded source...

Enhanced IGRP

The second routing protocol available to MKS is Enhanced IGRP. Using Enhanced IGRP is advantageous because hierarchical limitation is not required the router can leak across to neighbors. With Enhanced IGRP, MKS would define all the remote sites as Enhanced IGRP neighbors, and then would summarize their information into the core. The protocol does not require hierarchy, so summarization could be performed at any router and at any interface. All the single attached remote routers should not be...

Enhanced IGRP and bandwidth control

This section discusses Enhanced IGRP's bandwidth use. Because Enhanced IGRP is non-periodic, it consumes bandwidth only during an event. Enhanced IGRP is an interior gateway routing protocol designed for various networks and media. Enhanced IGRP is an advanced distance-vector protocol. The underlying concepts are the same as those of distance-vector protocols, except that Enhanced IGRP is a non-periodic incremental protocol. This differs from traditional distance-vector protocols, in which...

Enhanced IGRP and Distribute List

A distribution list is used to block routing information from being sent or received. This list can be applied on a per-routing protocol basis or a per-interface basis. When applied on a per-routing protocol basis, the distribution list will block all routing updates that are exiting or entering the protocol that do not pass the access-list. For example, consider this code router eigrp 1 network 10.0.0.0 distribute-list 1 in access-list 1 deny 10.10.10.0 0.0.0.255 access-list 1 permit any In...

Enhanced IGRP and Passive Interface

If you do not want to enable Enhanced IGRP on an interface, you must set it in passive mode. This prevents Enhanced IGRP from sending multicast hellos to an interface. The question then becomes When would you want to set a passive interface There are situations in which you should set Enhanced IGRP in passive mode. First, you would use the passive mode when a router is connected to a large number of customer sites and you do not want to run Enhanced IGRP on those links. If you are an Internet...

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...

Ethernet versus Token Passing Technologies

Token Ring, which is a token-passing LAN developed and supported by IBM, enjoyed enormous popularity during the days of IBM's Systems Network Architecture (SNA) networks, which developed in the 1970s. FDDI, a 100 Mbps optical fiber-based system, also was briefly popular due to its substantial speed advantage over the contemporary 10 Mbps Ethernet and its immunity to electrical interference. FDDI's largest drawback was the high cost of optical components. However, the lower cost and...

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...

Example

R 131.108.20.0 24 120 1 via 131.108.30.9,00 00 02,Serial2 0 C 131.108.10.0 24 is directly connected, Ethernet3 0 C 131.108.30.0 24 is directly connected, Serial2 0 The metric is the distance of the advertising router to the destination. In RIP, the metric is its hop count. Each router advertises a directly-connected interface with a hop count of one. When this information is passed to adjacent routers, the hop count is incremented by one, by every subsequent router. The maximum hop of a route...

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...

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...

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...

Feasible successor

This is a neighbor that meets the feasibility condition, which is a downstream neighbor to the destination, but not the least-cost path. The feasible successor is not used to forward data traffic to the destination. Figure 8-2 shows the route to network 140.10.1.0 24, which is advertised to router A by both router C and router B. The link speed between router A and router B is 45 Mb, and link speed between router A and router C is 1.544 Mb. Now, B is the shortest path to the destination and...

Feedback information

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Figure 11 Arpanet Network Hierarchy The Prelude to the Modern Internet Architecture

The ARPANET backbone consisted of a small number of core routers, operated by a single administrative body (the Internet Network Operations Center). A much larger number of non-core routers connected ARPANET customers to the backbone and were operated by the customers themselves. These non-core routers generally pointed a default route at one of the core routers, which were themselves defaultless. In other words, the core routers contained a routing entry for every network in the Internet.

Figure 110 The SNA Hierarchy and Comparison with the OSI Model

With only a limited scope for multiplexing, scalability proved to be more of a mainframe CPU issue than a problem of network or protocol design. SNA's demise was as much a result of its incapability of supporting peer-to-peer networking as its proprietary nature. Although IBM introduced its advanced peer-to-peer networking, which improved on the mediocre routing functions of standard SNA, this only eased the support issues for legacy systems, and opened the doors for router vendors rather than...

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...

Figure 13 NSS Router

One RT was the routing and control processor. As its name suggests, this processor performed routing algorithm calculations, created the IP routing table, and was responsible for the overall control of the box. Five RTs were packet-switch processors. Four contained a line card for WAN connectivity (448 Kbps initially, and T1 later). One the external PSP contained an Ethernet card for LAN connectivity. The PSPs were responsible for packet forwarding between line interfaces, and the design...

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...

Figure 1311 PIM Encoded Address Formats from RFC 2362

The wlue ts the number of contiguous bits left justed used as a mask which describes the address. It is less than or equal to the address length nn bits for the given Address Family and Encoding Type. If the message is sent for a single group then the Mask length must equal the address length in bits for thegiwn Address Family and Encoding Type. (e.g. 32 for Pvd native encoding and l S for IPve native encoding). Encoded Source Address Takes the to I lowing format...

Figure 1313 Pim Bootstrap Message

BOOTSTRAP messages are sent to the ALL-PIM-ROUTERS group (224.0.0.13) with a TTL of 1. Every router forwards such messages from every interface, except the one on which the message is received. This effectively forms a spanning tree. If BOOTSTRAP messages exceed the maximum packet size, they are fragmented. Fragments from the same message are identified by their common Fragment Tag. The Hash Mask Len indicates the length of hash-mask to use for mapping group addresses to RP. For IP, the...

Figure 134 IGMP Packet Formats

0123 4 5 6 7 390123456739012 3 4 5 673901 0123 4 5 6 7 390123456739012 3 4 5 673901 The group field may contain all zeros, which corresponds to a general query for membership information for all groups. This is the only message format supported by IGMPV1. In IGMPV2, the group address field may also be set to the particular group, in which case the querying router is soliciting membership reports for that group only. IGMPV2-capable hosts then respond with membership reports for that group. This...

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...

Figure 138 Pim Hello Message

If the holdtime expires without receiving a HELLO, a multicast router declares its neighbor dead and times out any associated multicast routing information. If the holdtime is set to Oxffff, the session is never timed out (useful for dial-on-demand circuits) if it is set to zero, the routing information is immediately timed out. Option types 2 to 16 are reserved by RFC 2362.

Figure 139 Pim Register Message

The source address of the unicast REGISTER message is the DR, and the destination is the rendezvous point (RP). The RP subsequently de-encapsulates the packet and forwards it down the multicast shared tree. This continues until a shortest-path tree is built from the RP to the source, and the RP sends a REGISTER-STOP message to the DR. The B bit is set to 1 if the router is a PMBR (PIM Multicast Border Router) for the source. A PMBR connects a dense mode PIM domain to a local sparse domain. The...

Figure 14 The T1 Nsfnet Backbone 1990 Regionals Added after 1990 Are Shaded

Supporting the NSFNET backbone routers was an evolutionary exercise, requiring close collaboration between the network operators and the code developers. This proved to be one of the great strengths of the team from Merit, IBM, and MCI, as they provided ongoing engineering to support a network that grew by as much as 500 percent per year. The rapid growth of the NSFNET, coupled with a requirement that the regional networks directly connect to each other rather than relying on the NSFNET...