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...

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...

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....

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...

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...

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...

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...

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...

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...

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...

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 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...

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...

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...

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...

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...

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...

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...

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...

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 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...

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...

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...

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 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 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 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...

Figure 144 Custom Queuing

Although custom queuing prevents any queue from monopolizing resources, the latency in queues with small byte counts can be greater during periods of congestion. It may be necessary to tune the relative size of these queues with the queue-list < list-number> queue < queue-number> limit command to achieve optimum results.

Figure 145 WFQ within the Router

The weight of a queue is inversely proportional to throughput. Higher IP precedence reduces the weight, and link-level congestion feedback increases it. The result is reduced jitter, leading to more predictable bandwidth availability to each application. There is also less chance that larger traffic flows will starve smaller flows of resources. This algorithm dynamically characterizes data flows these are referred to as conversations in WFQ terminology. The packet attributes used to identify a...

Figure 149 When the Best BGP Route Is Inserted Into the CEF Forwarding Table a Table Map May Be Applied via the

You can configure the IP precedence of a packet to be overwritten by the value in the CEF table via the bgp-policy source destination ip-prec-map interface subcommand. In addition, the packet may be tagged with a QoS-group-id via the bgp-policy source destination ip-qos-map interface subcommand. Either the source or the destination address can be used for the purpose of classifying the packet. After the precedence has been overwritten, or after a QoS tag has been applied, CAR and WRED...

Figure 151 NMS Architectures

When operated as a centralized facility, which represents the most cost-effective solution for smaller networks, the NMS will be located physically at a well-connected point in the network architecture. Although cost-effective, the centralized NMS introduces a single point of failure in two ways by the NMS being cut off from the network due to network failure and because of failure of the NMS itself. In addition, this model does not scale particularly well. Funneling of network-management data...

Figure 152 Location of Snmp Mibs within the Global OID Space

SMI data types are divided into three categories simple types, application-wide types, and simply constructed types. Table 15-1 lists each of these types. The SNMPv2 SMI introduces a number of new data types to work around limitations of the version 1 SMI. For example, the limitation of 32-bit integers became significant as devices became faster and 32-integer counters began to wrap around very quickly. As a result, 64-bit counters were introduced. Emanating from the root of the tree are three...

Figure 1615 Separate IGP to Carry Next Hop Information

Extending each regional OSPF is problematic because each router from each region will begin to send all the routes across. Remember that in OSPF you can summarize at the ABR and filter at the ASBR. Also, when configuring in OSPF, the process ID is insignificant, so router OSPF 1 on R1 can communicate with router OSPF 2 on router 3, unless these routers are running multiple processes. In cases in which routers are running multiple processes, the routers form an adjacency on common processes....

Figure 1619 Complete Network Setup for Alphacom

The configuration for router USA.Cal.R1 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 interface atm 1 0...

Figure 162 The North American Region

Figure 16-3 shows Alpha.com's Los Angeles, California campus. Within the campus, each department is located in separate buildings. For example, engineering is located in buildings B1 and B4. Figure 16-3 shows Alpha.com's Los Angeles, California campus. Within the campus, each department is located in separate buildings. For example, engineering is located in buildings B1 and B4. Figure 16-3. Campus for Alpha.com in California In this case, the departments would prefer to share resources. The...

Figure 1620 ISP Connections for Alphacom

Each region has its own ISP connection obviously, each region would prefer to use its own connection to the Internet. Proper addressing and network regionalization will improve asymmetric routing, although it will not be avoided completely. Alpha.com talks to ISP1 and sends it a more specific route from both North America and Europe (The routes sent from North America and Europe are shown in Figure 16-20.) Alpha.com also can send a less-specific route in case of failure. This way, Alpha.com...

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...

Figure 1629 Routing During Link Failure with an OSPF Single Area

If this setup is acceptable during failure, nothing must be done. If it is not acceptable, as in most cases, MKS must put an additional PVC between ABR1 and ABR2 in area 112. Now, the packet sent for R1 from ABR1 will not be forwarded to R2. Instead, it will be sent to ABR2 on the direct PVC, as shown in Figure 16-30. Figure 16-30. Additional Link between the ABRs to Avoid a Longer Path Figure 16-30. Additional Link between the ABRs to Avoid a Longer Path

Figure 1642 Dial Backup with OSPF and ODR

From Figure 16-42, it is apparent that an additional Ethernet interface is added between R1 and R2, and two access servers are added for the remote nodes to dial in. Recall that, for the single-attached sites, only a static route that covered the range was redistributed into the Enhanced IGRP process, both by R1 and R2. Only dual-attached remote nodes were leaked between R1 and R2. With the addition of the network access (NAS) servers, the same policies still exist. In case of failure, now all...

Figure 1643 Specific Route via the NAS Server

Because all the NAS servers permit only the default route via Enhanced IGRP, the only router that would query for 10.1.13.0 24 would be R1 when the primary connection goes down, and R2, and NAS1 in this case, when the PVC is restored between R1 and the remote router. During the initial failure, R1 loses the specific route to 10.1.13.0. It will query all its neighbors in this case, NAS1 through NAS7, R2, R3, and R4 because none of them had the specific route to 10.1.13.0 24. In such a case, R2,...

Figure 1645 Final Setup with OSPF as the Core Routing Protocol within a Region

This can be solved successfully by inserting some NAS servers on the ATM core routers, with one link to area 0 and the other on the dialing area. The number of areas is not an issue for MKS, but as the number of areas grows, it would become increasingly difficult to maintain a large number of areas in one router. This would require a large number of ISDN interfaces, which obviously do not scale very well, especially when you need to add redundancy to the backup path. This restriction arises...

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 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...

Figure 167 Defining VLANs for Alphacom

Although not all the VLANs would be able to connect with all the switches, it is wise to define all VLANs on all shared switches for redundancy. For example, Figure 16-7 shows that switch S3 connects to S7, which does not have VLAN 100 connected to it. One can argue that it is unnecessary to define VLAN 100 on S3 because a dual failure could occur, in which the links between S1 and S4 and between S1 and S2 go down. If you define VLAN 100 on S3, you would still have connectivity for VLAN 100...

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...

Figure 27 Introduction of CIDR and Route Aggregation

If you borrow six bits from the fourth octet and leave two bits for the host portion, the result is as follows In this case, the serial line addresses are 131.108.2.0 and 255.255.255.252, and the host addresses are 131.108.2.1 and 131.108.2.2. You cannot assign addresses of 131.108.2.0 and 131.108.2.3 as the host address because they become the broadcast address for this subnet. This way, you then can reach 131.108.2.252.255.255.252.0 with the host addresses of 131.108.2.253 and 131.108.2.254....

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...

Figure 34 10BaseT100BaseT Ethernet Topology

The theoretical data transmission rate of Ethernet is 10 Mbps. In practice, the data rates observed could vary widely with the number of computers on the LAN, their distribution and length of the LAN media, and the nature of the data flows. Excessive collision can slow the usable data rate to a crawl. This has led many users to embrace the 100 Mbps token passing technology of FDDI. However, with the introduction of Fast Ethernet technologies (100 Mbps) and Gigabit Ethernet technologies (1000...

Figure 41 Mesh Star Ring and Bus Topologies from top

Although initially attractive due to minimal dependence on complex electronics, the use of bus media, such as repeated Ethernet segments, is decreasing. For the most part, this is due to an increase in the reliability and flexibility of the technology that is implementing rings, stars, and meshes. In particular, bus LAN topologies are typically converted into stars using a LAN switch. This offers increased aggregate bandwidth and superior diagnostic capabilities. Operational experience has also...

Figure 42 Modularization of a Large Network

Each DC, which may house a LAN topology that is resilient to single node failure, forms the hub of a star distribution network for that region. Finally, the access network consists of both provider and customer premise equipment, which is typically homed to one or more access POPs. In the example in Figure 4-2, only three regions DCs and, at most, three POPs in a region are shown. However, the hierarchical model will scale much more than this using current commercial routers. A typical large IP...

Figure 51 First Second and Third Generation Packet Switches

Routers may be input-queued, or both input- and output-queued. If the switching fabric is slower than the sum of the interface card speeds, both input and output queuing can occur. Otherwise, queuing tends to occur at the outputs only, due to contention for the output interface. Queues traditionally were first-in, first-out with the introduction of service differentiation, however, per class-of-service queuing is increasingly common. In other words, routers may have to maintain queues for...

Figure 511 Router Routing Switching and Scheduling Overview

Increasingly, network operators are calling for sophisticated, yet scalable accounting, security, packet scheduling, and traffic-engineering features. New switching techniques, such as CEF, TAG, and Netflow, address these needs. The choice of switching mechanisms depends on the placement of the router within the network architecture The accounting and security features of Netflow and CEF are generally performed at the perimeter, whereas the performance of CEF, and the traffic engineering and...

Figure 54 Cisco AGS Architecture

Upon receiving a packet, cbus interface cards query the cbus controller for the destination line card. The cbus controller performs a local route-cache lookup for the destination if this is the first packet to the destination, the cache lookup fails and the cbus controller sends a query to the CSC card for a route-table lookup. The CSC returns the result to the cbus controller, which caches the result and responds to the query from the original line card. The receiving line card forwards the...

Figure 56 Cisco 7500 Architecture

Each VIP card participates in an interprocess communication system with the RSP over the CyBus. IPC maintains an up-to-date copy of the RSP's fast switching cache on each VIP card, enabling each to perform switching independent of the RSP, with the exception of the use of packet memory. Hence, within the constraints of the system bus, packet throughput is increased linearly with the number of VIP cards installed in the router. Switching local to a VIP is performed at more than 120,000 pps, and...

Figure 612 Supernet and Discontiguous Network Support Via the Internet

When the CIDR block route of 206.10.0.0 16 is received by router R1, this route typically is received via the Border Gateway Protocol (BGP) because ISPs run BGP with their customers to advertise routes. However, you cannot advertise this CIDR block in the RIPV1 network, because RIPV1 is a classful protocol and does not understand any route that does not have a regular class A, B, or C mask. To advertise this CIDR block into RIPV1, you must divide this network into all the class C mask networks....

Figure 614 Routing Loop Created Due to Physical Loop in RIP to IGRP Redistribution

As demonstrated in Figure 6-14, if R5 advertises network 170.10.0.0, and R1 is running both RIP and IGRP, then R1 is responsible for redistribution. R1 will redistribute 170.10.0.0 into IGRP and will advertise 170.10.0.0 to its IGRP neighbors, which are R2 and R3. Both R2 and R3 will advertise their best metric to each other about 170.10.0.0. R2 learns the route to 170.10.0.0 from R1, and the link speed between R1 and R2 is T3. R3 learns this route from R1, and the link speed between R1 and R3...

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...

Figure 69 Redistributing a Vlsm Ospf Route into RIP

Router rip network 131.108.0.0 redistribute static redistribute ospf 1 default-metric 1 ip route 131.108.10.0 255.255.255.0 nullO Now that you have a route with the same mask as that of the Ethernet of R1, this static route is redistributed into RIPV1 across the Ethernet of R1. R1 advertises this route, and all the routers behind the Ethernet of R1 in the RIP domain will have connectivity to all the VLSM destinations behind the R1 -OSPF domain. This is not a solution to VLSM for RIP, however it...

Figure 71 RIP Header for Version

The extension added in version 2 does not change the protocol, but the added extensions to version 1's message format grant the protocol the capability of accommodating today's networking needs. Recall that the first four octets in the RIP packet contain the header. The new RIP message format, shown in Figure 7-1, displays the command, version, IP address, metric, and address family identifier, all of which have the same meaning as in version 1. The Version field is set to 2 for this message....

Figure 73 A Rip Version 1 and 2 Mixed Environment

As shown in Figure 7-3, router R1 is running RIP and wants to exchange version 1 updates on the Frame Relay cloud. It exchanges version 2 updates on FDDI, and exchanges both version 1 and 2 updates on the Ethernet. You can configure the router to send and receive only version 1 updates. It is possible to send only version 2 updates or both versions. The configuration for R1 is as follows router rip network 131.108.0.0 interface serial 0 ip rip send version 1 ip rip receive version 1 interface...

Figure 75 Discontiguous Networks Across Multiple Interfaces

The routing table for R1 in Figure 7-5 would be as follows 131.108.0.0 16 is variably subnetted, 2 subnets, 2 masks R 131.108.0.0 16 120 1 via 140.10.10.9, 00 00 24, Serial 2 0 R 131.108.0.0 16 120 1 via 140.10.10.5, 00 00 02, Serial 3 0 C 131.108.10.0 24 is directly connected, Ethernet3 0 C 140.10.10.8 30 is directly connected, Serial 2 0 C 140.10.10.4 30 is directly connected, Serial 3 0. To solve the problem shown in Figure 7-5, you must disable auto-summary. This command, which tells the...

Figure 77 RIP and Suboptimal Routing Because of Hop Count

The problem illustrated in Figure 7-7 can be solved in two ways These solutions are discussed in the following sections. Using the Distance Command In Figure 7-7, R1 learns routes to subnet 10.10.1.0 via R2 and R3. The route via R2 is two hops away, and the route via R3 is one hop away. Because RIP does not consider real-time parameters such as bandwidth, it will install the route via R3 because it has fewer hops. To use the path through R2 instead of R3, you would use the distance command. The...

Figure 813 Enhanced IGRP and Query Scoping

Router D1 has 16 remote sites connected to it via Frame Relay each remote router advertises subnets from 131.108.1.0 24 to 131.108.15.0 24. D1 has all the specific routes in its routing table and can easily summarize all the subnets toward D2 and D3. If Ethernet 0 is the interface that connects D1 to D2 and D3, the interface configuration for Ethernet 0 on D1 would be as follows ip address 131.108.22.1 255.255.255.0 ip summary-address eigrp 1 131.108.0.0 255.255.240.0 With this configuration,...

Figure 815 Enhanced IGRP and Variance

Router D2 is using router D4 as its successor for network 10.1.4.0. If router D4's physical interface to network goes down, router D4 would send a query to router D2 for network 10.1.4.0. If router D2 has router D1 as its feasible successor, router D2 will send an unreachable message back to router D4. The unreachable message would be sent because of the distribution list, even though router D2 has a valid route to network 10.1.4.0.

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...

Flooding Over Pointto Point Links

A PDU is transmitted to the neighbor by an IS after an ISH is received from the neighbor. The purpose of this is to determine whether the neighbor is a level 1 or a level 2 intermediate system. After the neighbor is determined, the router then sends the CSNP on the point-to-point link. CSNPs are sent only the first time for the synchronization of a database. If the neighbor router discovers that it needs a newer instance of the LSP, it can request the LSP via the PSNP. The PSNP is also used for...

For Further Reading

Upper Saddle River, NJ Prentice Hall, 1997. Comer, Douglas. Internetworking with TCP IP, Volume 1. Upper Saddle River, NJ Prentice Hall, 1991. Dickie, Mark. Routing in Today's Internetworks. New York, NY John Wiley & Sons, 1994. Ford, Merilee (Editor), H. Kim Lew, Steve Spanier, and Tim Stevenson. InternetworkingTechnologies Handbook. Indianapolis, IN Cisco Press, 1997. Halabi, Bassam. Internet Routing Architectures. Indianapolis, IN Cisco Press, 1997. Keshav,...

Fundamentals of BGP Operation

BGP is structured around the concept that the Internet is divided into a number of Autonomous Systems (ASs). Before you learn how the protocol operates, you should become familiar with ASs. An Autonomous System (AS) is a network under a single administration, identified by a single two-byte number (1-65536), which is allocated by the InterNIC and is globally unique to the AS. Within an AS, private AS numbers may be used by BGP, but they must be translated to the official AS prior to...

Fundamentals of RIP Operation

RIP is a hop-count, metric-based routing protocol. Each router contains routing information about every possible destination in the autonomous system. Information maintained in the routing table includes the destination network or, in some cases, the host, the next hop along the path to the destination, the physical interface used to reach the next hop, and the metric. In Example 6-1, router R1 has received a route to destination 131.108.20.0 24 from 131.108.30.9. In this case, 131.108.30.9 is...

Future of the Internet

In this section, you will look into the future to discover the possible direction of the Internet and large-scale networks. The historical perspective in this chapter will help you understand where and why improvements were made as data networks have evolved and scaled. This chapter also illustrates a more salient point The use of ideas in development is often cyclic. This cyclical nature of development places a whole new meaning on the so-calledwheel of invention. Improvements in technology...

Glean adjacency

When a router is connected to a subnet, the FIB table maintains a prefix for the subnet rather than for each individual host. This subnet prefix points to a glean adjacency. When a packet must be forwarded to a specific host, the adjacency database is gleaned for the specific prefix. Output of show ip cef glean appears as follows Output of show ip cef glean appears as follows

Group Record M

Where each Group Record has the following internal format Where each Group Record has the following internal format This message enables a host to report to the querying router interest in traffic to a particular group address, from a specific set of sources. Therefore, in addition to the normal type 10 MEMBERSHIP REPORT message fields used by IGMPV1 V2, the IGMPV3 message includes the list of IP addresses in which this host is interested. This means that the querying router can perform...

Huband Spoke Setup

Essentially, there are two types of remote sites single-attached sites and dual-attached sites. MKS must decide how it will connect the hub and spoke sites, as shown in Figure 16-26. Figure 16-26. Hub-and-Spoke Setup for MKS Figure 16-26. Hub-and-Spoke Setup for MKS MKS has four choices for the hub-and-spoke setup Each of these choices is discussed in the following sections.

Nformation Frame Format

The frame is bounded by a Flag pattern. The Address field is used for indicating the secondary node involved for communication. Because primary is always either the source or the destination of the communication, that is why it is not in the SDLC frame. All the secondaries already know the primary's address. The Control field in the frame is altered according to the type of SDLC frame used, as explained in the list that follows.

Info

The first three bits of the Attribute Flags octet describe the general nature of the attribute that follows First bit 1 > optional, 0 > well-known Second bit 1 > transitive, 0 > non-transitive Third bit 1 > partial optional transitive, 0 > complete optional transitive These first two flags describe four attribute categories 01 Well-known, mandatory. These attributes must be included in every update containing NLRI, and are recognized by all compliant implementations. A notification...

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...

Interdomain Multicast MSDP and MBGP

How do RPs learn about sources in other PIM domains This problem is solved by the Multicast Source Discovery Protocol (MSDP). At the time of this writing, MSDP was still an Internet draft, and therefore this section describes only a work-in-progress. MSDP uses simple, one-to-one, BGP-like peering sessions to establish communication between RPs. Unlike BGP, however, no connection collision mechanism exists. Instead, the peer with the higher address listens on TCP port 639, whereas the other side...

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...

IP Routing

In the section on subnetting, you learned how a network is divided into smaller groups known as subnets. Each subnet is given an individual identity. All subnets need to be advertised by an algorithm within the autonomous system, and the network as a whole must be advertised outside the system. To propagate the network within the autonomous system and beyond, routing protocolsare used. Routing protocols are divided into two types First, Interior Gateway Protocols (IGPs) are used to propagate...

Limitations of RIPV1

Because RIPV1 has been given historic status, it always should be used with simple topologies that have simple reachability. The protocol should be operated in a network that has fixed subnetting and only default routes to connect to the Internet. RIP does not support CIDR, and it does not include any security functions. In today's complex networking environment, almost no network could be successful, given the limitations mentioned here. Therefore, RIP cannot scale to today's dynamic,...

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...

Making One Region the Registered AS while Running EBGP

Alpha.com could follow a third option, as shown in Figure 16-18. In this case, you do not need an extra router, but you must ensure that at least one of the AS regional routers is a registered AS number for Internet connection. Figure 16-18. EBGP Core with One Region Defined as the Registered AS Figure 16-18. EBGP Core with One Region Defined as the Registered AS The disadvantage of this setup is that only the site with the registered AS number can peer with the external world, so the other...

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...

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...