A 1021024 i successors rc it inaccessible u

replies, active ve (3 m 1& , query-origin Local origin P 10.1.2.9 24, 1 successors, FD is 26 a -e.e.1 .s-m, a successor* rc is ssesise-j.i, a * replies, active 00, query-origin Local origin a 10.37.1 .a 24, successorst Li 38Q71M7M, a Notice also that in each case, the neighbor 10.1.2.1 has its reply status flag (r) set. That is the neighbor from which replies have not yet been received. There may be no problem with the neighbor itself or with the link to the neighbor, but this information...

A70000ffdd000700003090c7df00

DFL Domain Specific Part (DSP) Formal identifier RDI Routing Domain identifier (Autonomous Syslem Mum be r) SEL Network Service Access Poinl (NSAP) Selector 12 * GOSIP Advanced Requirements Group, Government Open Systems Interconnection Profile (GOSIP) Version 2.0 Final Text , Federal Information Processing Standard, U.S. Department of Commerce, National Institute of Standards and Technology, October 1990. Also of interest in the examples of Figure 10.5 is the NSAP Selector (SEL). In each case,...

ABR to advertise a default route into an NSSA

CoLici c cenflect-aci. s sian- . isrp, h rip, w aobile, li EiGP D LUi.HP, LX EtflftP external, 0 (JLPr . ia OSPf inter area in (jspi iissA external type i, N2 oSPf nssa eternal type 2 L1 QSPI external type 1, L2 03PI external type 2, L E.UP i is IS, L1 is-is level 1, L2 - y is level ' - candidate default Gateway ci las I resort is 192.168.10,1 network 0.0.0.0 102. 55. 50.(J.132 iS SUbnetted, 1 i-uUiietS C 102,4 is directly connected, Loopbacko 1D2. 59.10.0-'iM is variably SubfltUCLi. 3 SuiulCT...

Access List Basics

An access list is a sequential series of filters. Each filter comprises some sort of matching criteria and an action. The action is always either permitor deny. The matching criteria may be as simple as a source address alternatively, they may be a more complex combination of source and destination addresses, protocol type, ports or sockets, and specifications of the state of certain flags, such as the TCP ACK bit. A packet is dropped into the top of the stack of filters (Figure B.2). At each...

Access List Monitoring and Accounting

It is useful to be able to examine an access list, or even all access lists, without having to display the entire router configuration file. The command show ip access-list displays an abbreviated syntax of all IP access lists on the router. If a specific access list is to be observed, the list may be specified by name or number (Figure B.15). If you leave off the ip keyword (show access-list), all access lists will be displayed. Figure B.15. The show ip access-list command displays an...

Access List Types

The actual configuration lines for the access list shown graphically on the right of ,Figure B.4 are access-list 9 deny 10.23.147.0 0.0.0.255 access-list 9 permit 10.0.0.0 0.255.255.255 Every filter layer of an access list is represented by one configuration line. The various components of an access list line are discussed shortly, but for now notice the number 9 in both lines. This number is the access list number, and it serves two purposes It links all the lines of this list together and...

Address Aggregation

Chapter 2, TCP IP Review, introduced the practice of subnetting, in which the address mask is extended into the host space in order to address multiple data links under one major network address. chapter 7 introduced the practice of variable-length subnet masking, in which the address mask is extended even more to create subnets within subnets. From an opposite perspective, a subnet address may be thought of as a summarization of a group of sub-subnets. And a major network address may be...

Addresses

FarlsMich reute 0000.0C0A.ZC51.00 Heute Lee* up for destination 3 ,30 c.Ga2c.5100 Using r-oute to lesest IS Iii level 2 'outer Syat& m 5rs ' sflPA lut(u-fate Stat a Holdtine Typo Protocol IS IS IS-IS uses nine PDU types in its processes, and each PDU is identified by a five-bit type number. The PDUs fall into three categories, as shown in Table 10.1. The first eight octets of all of the IS-IS PDUs are header fields that are common to all PDU types, as shown in Figure 10.15. These first...

Adjacent neighbors

When two routers have discovered each other as neighbors, they go through a process of synchronizing their databases in which they exchange and verify database information until their databases are identical. The details of database synchronization are described in Chapters 9, Open Shortest Path First, and 10, Integrated IS-IS. To perform this database synchronization, the neighbors must be adja cent that is, they must agree on certain protocol-specific parameters such as timers and support of...

Administrative distance

Notice that all static routes using subnet 10.1.20.0 are followed by a 50. This number specifies an administrative distance, which is a measure of preferability when duplicate paths to the same network are known, the router will prefer the path with the lower administrative distance. At first this idea sounds like a metric however, a metric specifies the preferability of a route, whereas an administrative distance specifies the preferability of the means by which the route was discovered. For...

Administrative Distances

The diversity of metrics presents another problem If a router is running more than one routing protocol and learns a route to the same destination from each of the protocols, which route should be selected Each protocol uses its own metric scheme to define the best route. Comparing routes with different metrics, such as cost and hop count, is like comparing apples and oranges. The answer to the problem is administrative distances. Just as metrics are assigned to routes so that the most...

Advertised as external

Carte L - connected, - fltotic, r - ISKP, K - PI , t) - mjbile, 5 - B& P D - EIGKP, EX - EIGRP entsrnal, 0 - CSPFj IA - OSPF Intel area tfl - OSPP USSA txteitifll type 1, H2 - SPF J1SSA extetnal type 5 El - Pf externa type 1, K3 - OsfF cxternal type 2, E - B(yP i - IS-IS, Li - IS-IS ievel-1, L2 - IS-IS level-2, * - candldate ilefau.lt tj - per-user Ataxie route, o - O K Gafee fty e> last KeaoiC i3 nob sefc 10.0,0.11 3 ia vdi ibiy s hne btedj aubnet , 2 masi'.a C 10.1.3 . D 14 in directly...

And the BDR

Process ID 1, Pouter ID 192.188.38.70, Network Type BROADCAST, Cost 10 lr-yiitiiiiir DoLijy ty 1 iiii,, KLathj DttOIHLf , Priority 1 tJisifln-ated Bouter i ID) iii2,lGO. ie.2,o4, Interface address 192.166.32.2 liaukuf) Doiignaii J router (ID) is.' .if)-Q_ ia.aa, interface adar-i 192.168.32,1 lifioi- in (ii-v Lconfigured, io 11 1B, Ocpfl < ip, wnrans*ii 5. Neighbor Count ts i, Adjacent noirjhiin ' r unt is 2 Adjacent with nelghfror 192.1 SB.38.00 (Backup Deslflnat& d Router) Adjacem ith...

And the holddown timer is started

des l - connected., S - itatio, I - IGEEj P - RIP, H - mobile, E - EGP D - BlUftP, EX - EIGP.P extttried, o - SPS, IA - QSPF intsr nr El - OSPE internal type- 1, S2 - OSPF CKtcrnal type l, E - EGr 1 - IS-IS, Ii - IS-IS leval- lj L2 - -IS level-2, * - CAfiiUiiftte (Je fault 1i - pcr-iujirr stfitlc route atcwiiy oi laut Trc oct i j nfft 3et I 19 168 . 1. a ' A is poiiiiily dorn, roiLtijiq Tfi.i 19 i .169. 3 .1, SciiilS I 192.163.2.0 24 100 6576 via igi.icE.3.1, 00 00 57, icrlalO C 192,1 8 .3.0...

Appendix A Tutorial Working with Binary and

The best way to gain an understanding of binary and hexadecimal numbering is to begin by examining the decimal numbering system. The decimal system is a base 10 numbering system (the root deci means ten). Base 10means that there are 10 digits with which to represent numbers 0through 9. Most likely, we work in base 10 because our ancient ancestors began counting their cattle and children and enemies on their fingers (in fact, the word digit means finger). The use of place values allows the...

Appendix B Tutorial Access Lists

Access lists are probably misnamed these days. As the name implies, the original intention of an access list was to permit or deny access of packets into, out of, or through a router. Access lists have become powerful tools for controlling the behavior of packets and frames. Their use falls into three categories (Figure B.1) Security filters protect the integrity of the router and the networks to which it is passing traffic. Typically, a security filter permits the passage of a few,...

Appendix F Solutions to Troubleshooting Exercises

Chapter 2 Chapter 3 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Chapter 11 Chapter 13 Chapter 14 1 For the following host addresses and subnet masks, find what subnet each address belongs to, the broadcast address of that subnet, and the range of host addresses for that subnet 2 You have been told to configure 192.168.13.175 on an interface with a mask of 255.255.255.240. Is there a problem If so, what is it A 192.168.13.175 28 is the broadcast address of subnet 192.168.13.160...

Are being advertised as type 1 external routes

Codes C - connected., - static, I - IGR.P, F - PIE, H - motile, S - 2& P D - EIGP.P, EK - EIGEP Eitteiiwil, O - OSPF, IA - OSPF intei itei HI - OSPF HSSA catc-rnnl type i, St - OSPF fSSA CHt iiml type Z El - OSPF evteihil type 1, Et - OSPF efctetiiftl type 2, E - EGP i - ISIS, bl - IS-IS JLtvcJL-1, I - IS-IS JLcttcJL- , * - t dcinylt t IR2.1 H.1.0 24 as dirictlw connectCil, Ethcrriit2 O t iS2.l 3,2.0 24 110 50 viii 192. t B .3 . 33, 00 21 20, EthernetD 192 3.0 21 Is subletted, i subnets C...

Area Addresses CLV

The Area Addresses CLV (Figure 10.21) is used to advertise the area addresses configured on the originating router. As the multiple Address Length Area Address fields imply, a router can be configured with multiple area addresses. There will never be more than three Address Length Area Address fields in PDUs originated by Cisco routers because that is the maximum number of area addresses supported. Figure 10.21. The Area Addresses CLV. Figure 10.21. The Area Addresses CLV. Figure 10.22 shows...

Area destinations

Nationai hoi . iT flatstiie OSPF .c_ ewit n ID (l.t.1.2) It a' _ik IL DV .'O.Ct jlgv ieq* L re ki_r 17 . 16. Ifti.e 1.1.1.1 13Z yin e _ -k IL ABV fl-Qyter Agi Seq* ire ks.r tT2.ie.IS2.6 1.1.1.1 t32 H8MMS34 OxAC-iD t72.1fi.219.12 1.1.1.2 1 4Sa IS S S 3 2 i Bx6B 6 The only destinations outside of area 1 in National's route table (Figure 9.100) are the serial links attached to Whitney. Yet another clue is revealed here The route entries are tagged as intra-area routes (O) if they were in area 0,...

Area ID

Areas are identified by a 32-bit Area ID. As Figure 9.20 shows, the Area ID may be expressed either as a decimal number or in dotted decimal, and the two formats may be used together on Cisco routers. The choice usually depends on which format is more convenient for identifying the particular Area ID. For example , area 0 and area 0.0.0.0 are equivalent, as are area 16 and area 0.0.0.16, and area 271 and area 0.0.1.15. In each of these cases, the decimal format would probably be preferred....

Asynchronous Updates

Figure 4.7 shows a group of routers connected to an Ethernet backbone. The routers should not broadcast their updates at the same time if they do, the update packets will collide. Yet this situation is exactly what can happen when a several routers share a broadcast network. System delays related to the processing of updates in the routers tend to cause the update timers to become synchronized. As a few routers become synchronized, collisions will begin to occur, further contributing to system...

Athens is Spartas gateway of last resort

TCjJ i C connected, 5 ta*iC. 1 - I RP. R RIP. f - nit-Li 1 . 3 BGP o it ftp, ex eigrp external, o - ospf, ia - o t inter area til usrf hysa external type i, n2 ospf nssa external type 2 Ei Uyi'F1 xtc.'-n i type 1,112- ospf t j( t l r.ii I type 2, L ELi - is-is, Li isis level-1, L2 isis level 2, - ajitiidati default ii per u r statte r-guie, o odr G t *iy Of la& t resort is 172.16,1.1 to nitngrK n. .a. p 192.168.1,0 24 126 1 via 172.16.2.2, 80 60 1ft, EtharnstO 1128 1 Via 72.10. 3.2, 80 60...

Authentication Information CLV

The Authentication Information CLV (Figure 10.26) is used when authentication is configured. The Authentication Type field contains a number between 0 and 255 that specifies the type of authentication used and hence the type of information contained in the Authentication Value field. The only authentication type currently defined by ISO 10589 or supported by Cisco is a cleartext password, which is Authentication Type 1. Figure 10.26. The Authentication Information CLV. Figure 10.26. The...

Automonous system

The routing protocols that run within an autonomous system are referred to as Interior Gateway Protocols (IGPs). All the protocols given in this chapter as examples of distance vector or link state protocols are IGPs. Routing protocols that route between autonomous systems or routing domains are referred to as Exterior Gateway Protocols (EGPs). Whereas IGPs discover paths between networks, EGPs discover paths between autonomous systems. Examples of EGPs include the following Border Gateway...

Autonomous system external LSAs

Gcmes C connected, S siari- , I t HP, H HIP, M mcbilu. 13 ESGf i) LifiHH, Li EiGftP external, Dsw , ia QSP( iiitflf area l t 'i external type i, E2 qspf g*iernai type 2, l lu ' I ts tS. LI LS S iflval i, 1 13 level , candidate default O E2 192,166.10S. 0 24 110 10 VLH 192 , 1GB.20.2, S& rialO 0 2 192. t . 140.0 24 110. 10 via 192 . & - , S& rialO .2 ,0 24 I 110 19 Via -Si . . 1& F .2B.2 , OO 50, Serial 0 I 2 193. IBB. 70,0 24 I 110 IB Via 132. 1 68. 20 . 2, 0 00 -D , Ser alo 12...

Basic Uses of Route Maps

Route maps can be used for both redistribution and for policy routing. They are also used frequently in large-scale Border Gateway Protocol (BGP) implementations. Although redistribution has been covered extensively in previous chapters, this chapter introduces the topic of policy routing. Policy routes are nothing more than sophisticated static routes. Whereas static routes forward a packet to a specified next hop based on the destination address of the packet, policy routes forward a packet...

Been translated into type 5 LSAs by Goya 192168503

Type 7 AS External Link Stales (Area 192.166.10,O) Type 7 AS External Link Stales (Area 192.166.10,O) Several configuration options are available for the ABR. First, the no-summary option can be used with the area nssa command to block the flooding of type 3 and type 4 LSAs into the NSSA. To turn area 192.168.10.0 into a somewhat schizophrenically named totally stubby not-so-stubby area, Goya's configuration would be router ospf 30 network 192.168.20.0 0.0.0.3 area 0 network 192.168.10.0...

Better match of host cs address than is the first route

CjriS C coniwctetl, Static, T iCflP, 4 HIP, H Otile. EL JP U ElOUP, .X EIQRR r ernal r OSPF, ft C l inter rea E1 S f externa. ly c 1. E2 o-S f external tyf 2. L SP i iS-iS. L1 IS'IS level 1,1 IS-IS teuel 2, cand ate default u par-user star it runic iir .-.- y c 1 l it re urt l 175.19-35-1 is network B-.U.Si.U 172.1 f-. n. S) -li i , variably s jl> nt 11 ml , IB subnets, a rusks R 172.19.35.128 27 i 120 11 via 172.19.35.3, M & 0 r. Llht m'l F 172.19.35.16fl 27 126 11 via 172,13.35.3, M SU...

Bicycles with Motors

One of the difficulties of decentralized computing is that it isolates users from one another and from the data and applications they may need to use in common. When a file is created, how is it shared with Tom, Dick, and Harriet down the hall The early solution to this was the storied SneakerNet Put the file on floppy disks and hand carry them to the necessary destinations. But what happens when Tom, Dick, and Harriet modify their copies of the file How does one ensure that all information in...

C iM 16 0LwptmckD

15a 10 jn.-.i > i hi* 1 ip route 10.1.30.0 255.255.255.0 10.1.10.2 ip route 10.1.10.0 255.255.255.0 192.168.1.194 ip route 192.168.1.192 255.255.255.224 192.168.1. If Pooh needs to send a packet to host 10.1.30.25, it will look into its route table and find that the subnet is reachable via 10.1.10.2. Because that address is not on a directly connected network, Pooh must again consult the table to find that network 10.1.10.0 is reachable via 192.168.1.194. That subnet is also not directly...

Case Study A Basic Eigrp Configuration

Like IGRP, EIGRP requires only two steps to begin the routing process 1. Enable EIGRP with the command router eigrp process-id. 2. Specify each major network on which to run EIGRP with the network command. The process ID may be any number between 1 and 65535 (0 is not allowed), and it may be arbitrarily chosen by the network administrator, as long as it is the same for all EIGRP processes in all routers that must share information. Alternatively, the number may be an InterNIC-assigned...

Case Study A Basic IGRP Configuration

Only two steps are necessary to configure IGRP 1. Enable IGRP with the command router igrp process-id. 2. Specify each major network on which to run IGRP with the network command. The process ID is carried in the 16-bit autonomous system field of the update packet. The selection of a process ID is arbitrary any number between 1 and 65,535 (0 is not allowed) can be used, as long as it is used consistently on all routers that must share information via that particular IGRP process. Figure 6.11...

Case Study A Basic OSPF Configuration

The three steps necessary to begin a basic OSPF process are 1. Determine the area to which each router interface will be attached. 2. Enable OSPF with the command router ospfprocess-id. 3. Specify the interfaces on which to run OSPF, and their areas, with the network area command. Unlike the process ID associated with IGRP and EIGRP, the OSPF process ID is not an autonomous system number. The process ID can be any positive integer and has no significance outside the router on which it is...

Case Study A Basic RIP Configuration

Only two steps are necessary to configure RIP 1. Enable RIP with the command router rip. 2. Specify each major network on which to run RIP with the net work command. Figure 5.8 shows a four-router internetwork, with four major network numbers. Router Goober is attached to two subnets of network 172.17.0.0. The commands necessary to enable RIP are Figure 5.8. Both Andy and Barney are border routers between class-level networks. Figure 5.8. Both Andy and Barney are border routers between...

Case Study A Basic RIPv2 Configuration

By default, a RIP process configured on a Cisco router sends only RIPvl messages but listens to both RIPvl and RIPv2. This default is changed with the version command, as in the following example network 172.25.0.0 network 192.168.50.0 In this mode, the router sends and receives only RIPv2 messages. Likewise, the router can be configured to send and receive only RIPvl messages network 172.25.0.0 network 192.168.50.0 The default behavior can be restored by entering the c ommand no version in...

Case Study A Missing Neighbor

Figure 8.45 shows a small EIGRP internetwork. Users are complaining that subnet 192.168.16.224 28 is unreachable. An examination of the route tables reveals that something is wrong at router Grissom (Figure 8.46). 17 17 When troubleshooting an internetwork, it is a good practice to verify that the addresses of all router interfaces belong to the correct subnet. Figure 8.45. Subnet 192.168.16.224 28 is not reachable through Grissom in this example of an EIGRP Figure 8.45. Subnet 192.168.16.224...

Case Study A Protocol Migration

The distance command, when used without any optional parameters, specifies the administrative distance to be assigned to routes learned from a particular routing protocol. On first consideration, this action may not seem to be a route filtering function, but it is. When multiple routing protocols are running, routes are accepted or rejected based on their administrative distances. The internetwork in Figure 13.7 is running RIP, and there is a plan to convert to EIGRP. Several methods exist for...

Case Study Address Aggregation

A new router is added to the internetwork in Figure 8.43. The five network addresses that Earhart must advertise to Yeager can be summarized with two aggregate addresses. Earhart's configuration will be Figure 8.43. Earhart is advertising two aggregate addresses to Yeager. Figure 8.43. Earhart is advertising two aggregate addresses to Yeager. interface Ethernet1 ip address 10.15.15.254 255.255.255.252 ip summary-address eigrp 15 172.0.0.0 255.0.0.0 ip summary-address eigrp 15 192.168.16.0...

Case Study Address Summarization

Although stub areas conserve resources within non-backbone areas by preventing certain LSAs from entering, these areas do nothing to conserve resources on the backbone. All addresses within an area are still advertised out to the backbone. This situation is where address summarization can help. Like stub areas, address summarization conserves resources by reducing the number of LSAs flooded. It also conserves resources by hiding instabilities. For example, a flapping subnet will cause LSAs to...

Case Study An Area Migration

To change area addresses in an OSPF domain, downtime must be scheduled. However, IS-IS is designed to allow areas to be changed nondisruptively. As discussed in Operation of Integrated IS-IS, Cisco routers can be configured with up to three area addresses. For two routers to form an L1 adjacency, they must have at least one area address in common. With multiple area addresses allowed, a new adjacency can take over while an old adjacency is being broken. This approach is useful when areas are...

Case Study Authentication

Cisco's implementation of RIPv2 message authentication includes the choice of simple password or MD5 authentication, and the option of defining multiple keys, or passwords, on a key chain. The router may then be configured to use different keys at different times. The steps for setting up RIPv2 authentication follow. 1. Define a key chain with a name. 2. Define the key or keys on the key chain. 3. Enable authentication on an interface and specify the key chain to be used. 4. Specify whether the...

Case Study Configuring OnDemand Routing

ODR is enabled with a single command, router odr. No networks or other parameters must be specified. CDP is enabled by default it needs to be enabled only if it has been turned off for some reason. The command to enable the CDP process on a router is cdp run to enable CDP on a specific interface, the command is cdp enable. Figure 12.17 shows a typical hub-and-spoke topology. To configure ODR, the hub router will have the router odr command. As long as all routers are running IOS 11.2 or later...

Case Study Configuring Unicast Updates

Next, router Bea is added to the Ethernet link that Andy and Floyd share (Figure 5.11). The no-RIP policy between Andy and Floyd remains in place, but now Bea and Andy, as well as Bea and Floyd, must exchange RIP advertisements. Figure 5.11. No RIP updates should be exchanged between Andy and Floyd, but both should exchange Figure 5.11. No RIP updates should be exchanged between Andy and Floyd, but both should exchange The configuration of Bea is straightforward network 192.168.12.0 network...

Case Study Disabling Automatic Summarization

By default, EIGRP summarizes at network boundaries as do the protocols covered in previous chapters. Unlike those protocols, however, EIGRP's automatic summarization can be disabled. Figure 8.42 shows a situation in which disabling summarization is useful. Figure 8.42. Disabling automatic summarization at Cochran and Lindbergh prevents ambiguous routing to Figure 8.42. Disabling automatic summarization at Cochran and Lindbergh prevents ambiguous routing to New Ethernet links have been added to...

Case Study Discontiguous Subnets

In Figure 5.13, another router has been added to the internetwork with a subnet 10.33.32.0 20 on its El interface. The problem is that the other subnet of network 10.0.0.0, 10.33.0.0 20, is connected to Barney, and the only route between the subnets is via 192.168.83.0 and 192.168.12.0 two entirely different networks. As a result, network 10.0.0.0 is discontiguous. Figure 5.13. Classful protocols such as RIP and IGRP cannot route a topology in which the subnets of network 10.0.0.0 are separated...

Case Study Filtering Specific Routes

Figure 13.2 shows a portion of an internetwork running RIPv2. Barkis is providing connectivity to the rest of the internet via Traddles. In addition to the 700 specific routes within BigNet, Traddles is advertising a default route to Barkis. Because of the default route, Barkis, Micawber, Peggotty, and Heep do not need to know the other 700 routes in BigNet. So the objective is to configure a filter at Barkis that will accept only the default route from Traddles and reject all other routes....

Case Study Integrated ISIS on NBMA Networks

Figure 10.64 shows four routers running IS-IS connected by a partially meshed Frame Relay network. The IP addresses, DLCIs, and NETs are shown. The IS-IS configurations of all routers have been verified as correct, and no authentication is configured. Figure 10.64. IS-IS is not establishing adjacencies across the Frame Relay network. Figure 10.64. IS-IS is not establishing adjacencies across the Frame Relay network. The problem with this internetwork is that no routes are being discovered...

Case Study Manipulating RIP Metrics

A serial link, to be used as a backup, has been added between Ernest_T and Barney (Figure 5.16). This link should be used only if the route via Andy fails. The problem is that the path between Barney's 10.33.0.0 subnet and Ernest_T's 10.33.32.0 subnet is 1 hop via the serial link and 2 hops via the preferred Ethernet links. Under normal circumstances, RIP will choose the serial link. Figure 5.16. RIP metrics must be manipulated so that the 2-hop Ethernet route between Barney and Ernest_T will...

Case Study Misconfigured Summarization

Figure 9.102 shows a backbone area and three attached areas. To reduce the size of the link state database and to increase the stability of the internetwork, summarization will be used between areas. Figure 9.102. The summary addresses shown for each area will be advertised into area 0. Area 0 will also Figure 9.102. The summary addresses shown for each area will be advertised into area 0. Area 0 will also The individual subnets of the three nonbackbone areas are summarized with the addresses...

Case Study Multiple IGRP Processes

Two new routers, Lovett and Harriman, have been added to the internetwork (Figure 6.18). A decision has been made to create two IGRP autonomous system domains in the internetwork with no communications between the two. Figure 6.19 shows the two autonomous systems and the related links for each. Figure 6.18. Separate routing domains are to be created in this internetwork. Figure 6.18. Separate routing domains are to be created in this internetwork. Figure 6.19. The routers Harriman and Acheson...

Case Study Multiple Redistribution Points

Figure 13.12 shows an internetwork very similar to the one depicted in Figure 11.3. Recall from the associated discussion in Chapter 11 that the problem with multiple redistribution points is that administrative distances can cause routers to choose undesirable paths. In some cases, route loops and black holes can result. For example, Bumble's routing table (Figure 13.13) shows that it is routing to network 192.168.6.0 through Blathers, rather than using the preferable route through Monks....

Case Study NotSoStubby Areas

The earlier case study, OSPF and Secondary Interfaces, left off with Matisse accepting routes from Dali via RIP and redistributing them into the OSPF domain (see Figure 9.68). This step makes Matisse an ASBR and by extension makes area 192.168.10.0 ineligible to become a stub or totally stubby area. However, there is no need for AS External LSAs to enter the area from the backbone area therefore area 192.168.10.0 can be configured as an NSSA. The configuration at Matisse is router ospf 40...

Laying the Foundations

If you are a beginner, or your internetworking experience is limited, your first step is to get a solid grip on the basics of both internetworking and Cisco routers. This effort will involve both classroom training and self-study. Through its training partners, Cisco offers many hands-on training classes. You should attend as many of these classes as your time and resources allow, but of particular importance are Introduction to Cisco Router Configuration (ICRC) Advanced Cisco Router...

Case Study OSPF and Secondary Addresses

Two rules are related to the use of secondary addresses in an OSPF environment 1. OSPF will advertise a secondary network or subnet only if it is also running on the primary network or subnet. 2. OSPF sees secondary networks as stub networks (networks on which there are no OSPF neighbors) and therefore will not send Hellos on them. Consequently, no adjacencies can be established on secondary networks. Figure 9.65 shows the DNS server and an additional router attached to the E0 interface of...

Case Study OSPF over Demand Circuits

OSPF over demand circuits is easily configured by adding the command ip ospf demand-circuit to the interface connected to the demand circuit. Only one end of a point-to-point circuit, or the multipoint side of a point-to-multipoint circuit, needs to be declared a demand circuit. In most cases, OSPF over demand circuits should not be implemented across a broadcast medium. On such a network, the Hello packets cannot be suppressed, and the link will stay up. If the virtual circuits in Figure 9.92...

Case Study Passive Interfaces

The router Floyd has been added to the internetwork (Figure 5.10). It is desired that no RIP advertisements be exchanged between Floyd and Andy. This is easy enough at Floyd Figure 5.10. Network policy calls for no RIP exchanges between Andy and Floyd. Figure 5.10. Network policy calls for no RIP exchanges between Andy and Floyd. Floyd(config-router) network 192.168.100.0 By not including a network statement for 192.168.12.0, Floyd will not advertise on interface 192.168.12.66. Andy, however,...

Case Study Redistributing EIGRP and OSPF

The internetwork of Figure 11.19 has an OSPF domain and two EIGRP domains. Router Hodges is running OSPF process 1. Podres is running EIGRP process 1, and EIGRP process 2 is running on Snider and Campanella. Robinson has the following configuration Figure 11.19. Hodges is running OSPF, and Podres is running EIGRP 1. Snider and Campanella are running Figure 11.19. Hodges is running OSPF, and Podres is running EIGRP 1. Snider and Campanella are running router eigrp 1 redistribute ospf 1 metric...

Case Study Redistributing ISIS and RIP

In the internetwork of Figure 11.30, Aaron is running IS-IS, Williams is running RIPv1, and Mays is redistributing. Mays' IS-IS configuration is Figure 11.30. Router Mays is redistributing RIP into IS-IS and IS-IS into RIP. Figure 11.30. Router Mays is redistributing RIP into IS-IS and IS-IS into RIP. redistribute rip metric 0 metric-type internal level-2 net 01.0001.0000.0c76.5432.00 redistribute rip metric 0 metric-type internal level-2 net 01.0001.0000.0c76.5432.00 router rip redistribute...

Case Study Redistribution and Route Summarization

Cisco's EIGRP, OSPF, and IS-IS implementations have the capability to summarize redistributed routes. This case study examines summarization for EIGRP and OSPF the following case study examines IS-IS summarization. The first thing to note is that summarization is useful only if the IP subnet addresses have been planned for summarization. For example, the subnets of 192.168.3.0 within the OSPF domain in Figure 11.19 all fall under the summary address 192.168.3.0 25. The subnets of the same major...

Case Study Redistribution with IGRP

Redistribution between routing protocols is covered in Chapter 11, but it is worth noting here that if an IGRP process and an EIGRP process have the same process IDs, they will redistribute automatically. In Figure 8.38, router Curtiss has the following configuration Figure 8.38. If Earhart is configured with both EIGRP and with IGRP, using the same process ID for both, route information will be redistributed. Figure 8.38. If Earhart is configured with both EIGRP and with IGRP, using the same...

Case Study Route Summarization

Route summarization between areas in a link state protocol is introduced in Chapter 9. A more complete discussion of summarization, in the context of default routes, is presented in Chapter 12. Briefly, summary routes are useful because They reduce the size of LSPs, which reduces the size of the link state database consequently, memory and CPU are conserved. They hide instabilities within areas. If an address within a summary range changes or a link changes state, the change is not advertised...

Case Study Setting Maximum Paths

The maximum number of routes over which IGRP can load balance is set with the maximum-paths paths command. Paths may be any number from one to six in IOS 11.0 and later and any number from one to four in earlier versions. The default for all versions is four. Figure 6.16 shows three parallel paths of varying costs from McCloy to network 172.18.0.0. The network administrator wants to load balance over a maximum of only two of these routes while ensuring that if either of these paths should fail,...

Case Study Setting Router IDs with Loopback Interfaces

Suppose router Matisse from Figure 9.61 has been configured in a staging center and then sent to the field to be installed. During the bootup, the router reports that it cannot allocate a Router ID, and it seems to report the network area commands as configuration errors (Figure 9.63). Worse, the OSPF commands are no longer in the running configuration. Figure 9.63. OSPF will not boot if it cannot find an active IP address for its Router ID. Cisco internetwork Operating 5iys or Software I OS it...

Case Study Static Default Routes

Ip route 0.0.0.0 0.0.0.0 192.168.1.82 The static route configures the default route address of 0.0.0.0, and uses a mask that is also 0.0.0.0. A common mistake made by people configuring default routes for the first time is to use an all-ones mask instead of an all-zeros mask, such as ip route 0.0.0.0 255.255.255.255 192.168.1.82 An all-ones mask would configure a host route to 0.0.0.0, and the only packets that would match this address would be those with a destination address of 0.0.0.0. The...

Case Study Stub Areas

Because no type 5 LSAs are being originated within area 1, it can be configured as a stub area. Note that when an attached area is configured as a stub area, the Hellos originated by the router into that area will have E 0 in the Options field. Any router receiving these Hellos, which is not similarly configured, will drop the packets, and an adjacency will not be established. If there is an existing adjacency, it will be broken. Consequently, if an operational area is going to be reconfigured...

Case Study The Default Information Originate Command

An OSPF ASBR and an IS-IS interdomain router will not automatically advertise a default route into their routing domains, even when one exists. For example, suppose Athens in Figure 12.9 is configured for OSPF and given a static default route into BigNet router ospf 1 network 172.16.0.0 0.0.255.255 area 0 Figure 12.13 shows the routing tables of Athens and Sparta. Although the static route has caused the gateway of last resort to be set at Athens, Sparta has no knowledge of the default route....

Case Study Totally Stubby Areas

Totally stubby areas are configured by placing the keyword no-sum mary at the end of the area stub command. This step is necessary only at the ABR the Internal Routers use the standard stub area configuration. To make area 1 of the sample internet a totally stubby area, Chardin's configuration would be router ospf 20 network 192.168.30.0 0.0.0.255 area 1 network 192.168.20.0 0.0.0.255 area 0 area 1 stub no-summary Figure 9.76 shows that the LSAs in Rubens' database have been reduced to three...

Case Study Unequal Cost Load Balancing

Given up to six parallel routes of equal cost, 5 IGRP will do equal-cost load balancing under the same fast process switching constraints as RIP. Unlike RIP, IGRP can also perform unequal-cost load balancing. An additional serial link has been added between Acheson and Kennan in Figure 6.12, with a configured bandwidth of 256K. The goal is to have Acheson perform unequal-cost load balancing across these two links-spreading the traffic load inversely proportional to the metrics of the link. 5...

Case Study Unequal Cost Load Balancing Again

The entire internetwork of Figure 6.20 is routed with a single IGRP process, and the bandwidths for the serial links are configured to the numbers shown. Default delays are used. Notice that the addresses of the link between Lovett and Harriman are different from the previous examples. Because network 10.0.0.0 can be reached from Acheson not only by the two serial links but also via the Ethernet to Lovett, the network administrator wants to distribute the traffic proportionately among all three...

Case Study Using VLSM

Referring again to Figure 7.10, the subnet 172.25.150.0 24 has been assigned to the internet shown. That subnet has been further subnetted to fit the various data links by expanding the mask to 28 bits the available sub-subnets, in binary and dotted decimal, are shown in Figure 7.13. Each of the subnets1101 will have, according to the 2n - 2 formula, 14 host addresses. Out of these, 172.25.150.32, 172.25.150.192, and 172.25.150.224 have been used. 101 Now that the concept should be firmly in...

Case Study Virtual Links

Figure 9.89 shows an internetwork with a poorly designed backbone area. If the link between routers Hokusai and Hiroshige fails, the backbone will be partitioned. As a result, routers Sesshiu and Okyo will be unable to communicate with each other. If these two routers are ABRs to separate areas, inter-area traffic between those areas will also be blocked. Figure 9.89. A failure of the link between Hokusai and Hiroshige will partition the backbone area. Figure 9.89. A failure of the link between...

Causing error messages when area 0 Hellos are received

Internet s I 72,15.1t3.IS, Area 1 ProcetG 10 S, Pouter ID 1.1.1.1, Hetwark ypi POlNTJTO POIl T, Li'. '-artr '. Leliy 1 . Ss t f-UIM '3 P IHT, configured. 'B. liflF.d -J -, .is t.'l , Met r. nsr i Hello due i (M 0e < 5 Heigh tier Uount is 0, Adjacent neighbor count is 9 flhitney*sbow is ziqt interface serial i l'un is .(). line is us Internet Azdre s ' 12. . i . 1 'I, Area 1 Process 10 fi, < odte- ) i.i.i.i, hitwork 'ype POINT lO POIMT, Cost 64 ranao t Ue.iy 1 . State P 1M '0 POINT, 'l-E.-...

Basic Concepts Internetworks Routers and Addresses

Once upon a time, computing power and data storage were centralized. Mainframes were locked away in climate-controlled, highly secure rooms, watched over by a priesthood of IS administrators. Contact with a computer was typically accomplished by bringing a stack of Hollerith cards to the priests, who interceded on our behalf with the Big Kahuna. The advent of the minicomputer took the computers out of the IS temple of corporations and universities and brought them to the departmental level. For...

Chapter

1 shows the interfaces, interface addresses, and subnet masks of 11 routers. The table also designates that routers belong in the same area. Write Integrated IS-IS configurations for the routers, using the following guidelines A This solution uses a System ID of 0000.1234.abcX, where X is a number that makes the router unique within the IS-IS domain. The System ID is six octets, which is required by Cisco IOS. The minimum NET length is eight octets, one of which is the SEL, so the area address...

1

A Although IS-IS has formed an adjacency, the IP addresses are not on the same subnet and therefore the interfaces do not pass traffic. 2 shows debug messages from a router that is not establishing an adjacency with a neighbor on its interfaces T00. What is wrong A The router sends only L1 Hellos, indicating that it is an 5 L1 router. It receives only L2 Hellos from 0000.3090.c7df, indicating that it is an L2 router. 1 In the case study Redistributing IGRP and RIP, the following configuration...

Route Redistribution

Principles of Redistribution Redistributing from Classless to Classful Protocols Case Study Redistributing IGRP and RIP Case Study Redistributing EIGRP and OSPF Case Study Redistribution and Route Summarization Case Study Redistributing IS-IS and RIP Case Study Redistributing Static Routes A router performs redistribution when it uses a routing protocol to advertise routes that were learned by some other means. Those other means may be another routing protocol, static routes, or a direct...

Route Maps

Case Study Policy Routing and Quality of Service Routing Case Study Route Maps and Redistribution Route maps are similar to access lists they both have criteria for matching the details of certain packets and an action of permitting or denying those packets. Unlike access lists, though, route maps can add to each match criterion a set criterion that actually changes the packet in a specified manner, or changes route information in a specified manner.

TCPIP Review

The purpose of this chapter is to examine the details of the protocols that enable, control, or contribute to the routing of TCP IP, not to do an in-depth study of the TCP IP protocol suite. Several books on the recommended reading list at the end of the chapter cover the subject in depth. Read at least one. Conceived in the early 1970s by Vint Cerf and Bob Kahn, TCP IP and its layered protocol architecture predates the ISO's OSI reference model. A brief review of TCP IP's layers will be useful...

Static Routing

An important observation from Chapter 2, TCP IP Review, is that the data link physical layers and the transport network layers, as defined by the OSI model, perform very similar duties They provide the means for conveying data from a source to a destination across some path. The difference is that the data link physical layers provide communications across a physical path, whereas the transport network layers provide communications across a logical or virtual path made up of a series of data...

Routing Information Protocol RIP

RIP Timers and Stability Features RIP Message Format Request Message Types Classful Routing Case Study A Basic RIP Configuration Case Study Passive Interfaces Configuring Unicast Updates Case Study Discontiguous Subnets Case Study Manipulating RIP Metrics The oldest of the distance vector IP routing protocols still in widespread use, RIP currently exists in two versions. This chapter deals with version 1 of RIP. Chapter 7, Routing Information Protocol Version 2, covers version 2, which adds...

Interior Gateway Routing Protocol IGRP

IGRP Timers and Stability Features IGRP Metrics IGRP Packet Format Case Study A Basic IGRP Configuration Case Study Unequal-Cost Load Balancing Case Study Setting Maximum Paths Case Study Multiple IGRP Processes o Case Study Unequal-Cost Load Balancing, Again o Case Study A Segmented Network Cisco developed IGRP in the mid-1980s as an answer to the limitations of RIP, the most important of which are the hop count metric and the 15-hop internetwork size. IGRP calculates a composite metric from a...

Classful Routing Directly Connected Subnets

Classful route lookups can be illustrated with three examples (referring to Figure 5.5) 1. If a packet with a destination address of 192.168.35.3 enters this router, no match for network 192.168.35.0 is found in the routing table and the packet is dropped. 2. If a packet with a destination address of 172.25.33.89 enters the router, a match is made to class B network 172.25.0.0 24. The subnets listed for this network are then examined no match can be made for subnet 172.25.33.0, so that packet,...

Classful Routing Summarization at Boundary Routers

A question arises from the preceding discussion How does a RIP process interpret the subnet of a major network if it has no interfaces attached to that network Without an interface on the class A, B, or C network of the destination, the router has no way of knowing the correct subnet mask to use and therefore no way of correctly identifying the subnet. The solution is simple If a router has no direct attachments to the network, then it needs only a single route entry pointing toward a router...

Classful Routing Summary

The defining characteristic of a classful routing protocol is that it does not advertise an address mask along with the advertised destination address. Therefore, a classful routing protocol must first match the major class A, B, or C network portion of a destination address. For every packet passing through the router 1. If the destination address is a member of a directly connected major network, the subnet mask configured on the interface attached to that network will be used to determine...

Classless Route Lookups

Chapter 5, Routing Information Protocol (RIP), explains classful route lookups, in which a destination address is first matched to its major network address in the routing table and is then matched to a subnet of the major network. If no match is found at either of these steps, the packet is dropped. This default behavior can be changed, even for classful routing protocols such as RIPv1 and IGRP, by entering the global command ip class less. When a router performs classless route lookups, it...

Classless Routing Protocols

The true defining characteristic of classless routing protocols is the capability to carry subnet masks in their route advertisements. One benefit of having a mask associated with each route is that the all-zeros and all-ones subnets are now available for use. Chapter 2, TCP IP Review, explained that classful routing protocols cannot distinguish between an all-zeros subnet (172.16.0.0, for example) and the major network number (172.16.0.0). Likewise, they cannot distinguish between a broadcast...

CLV Fields

The variable-length fields following the PDU-specific fields are Code Length Value(CLV)m triplets, as shown in Figure 10.17. The Code is a number specifying the information content of the value field, the Length specifies the length of the Value field, and the Value field is the information itself. As the one-octet size of the Length field implies, the maximum size of the Value field is 255 octets. 17 The acronym CLV is not used in ISO 10589, but is used here for convenience. You are already...

Commands

Neighbor ID Pri 5T< ite Utad rimo Address Interface chardin 1 i ull ea aa 19 , 168.20. 1 sf i-iai3 niiiLUFio i I (ILL Hfl ia LiHi IM,i66,i ,l Seriaii Goyasshow l(i osjii ii< it< it'< is(i OSPF Hotiter aii h ID (192 .16S .30-3 (Process ID 3 ) Hcjlcr Link Lares (Area & .0.S.0 . iiin it1 AOV ftoutar fi-nn tn ik un BX1B3I 192. Sunnsry Ncl Lin* ttatcs (Area B.fl.B.fl) nou tar Link siaiea (A a ifl2.iss.iB,B) Link id 1 cj2 . < 3fi. 50 . 3 192 . 1 h5e3.50 .4 AUV Hdulci' 03 cniikiu i Lir.j...

Common Characteristics

A typical distance vector routing protocol uses a routing algorithm in which routers periodically send routing updates to all neighbors by broadcasting their entire route tables.131 131 A notable exception to this convention is Cisco's Enhanced IGRP. EIGRP is a distance vector protocol, but its updates are not periodic, are not broadcasted, and do not contain the full route table. EIGRP is covered in Chapter 8, Enhanced Interior Gateway Routing Protocol (EIGRP). The preceding statement contains...

Configuration Exercises

1 The first octet rule says that the highest class C address is 223, but it is known that for eight bits the highest decimal number is 255. There are two more classes Class D addresses are for multicast, and class E addresses are for experimental usage. Class D addresses have, as their first four bits, 1110. What is the decimal range of the first octet of class D addresses 2 Select a subnet mask for 10.0.0.0 so that there will be at least 16,000 subnets with at least 700 host addresses...

Configuring Default Routes and ODR

Case Study The Default-Network Command Case Study The Default-Information-Originate Command Case Study Configuring On-Demand Routing Summarization has been examined in several chapters so far. Summarization conserves internetwork resources by reducing the size of routing tables and route advertisements. The smaller, simpler routing tables can also make management and troubleshooting easier. A summaryaddress is an address that represents several, sometimes many, more-specific addresses. For...

Configuring EIGRP

The basic configuratio n of EIGRP is so similar to the basic configuration of IGRP that instructors occasionally will instruct beginners to configure IGRP, but add an E. As mentioned in the previous section, the metric weights command is used the same way with EIGRP and IGRP. The traffic-share and variance commands are also used identically. For a review of these commands, please refer to Chapter 6. The case studies in this section demonstrate a basic EIGRP configuration and then examine...

Configuring IGRP

Although a few more configuration options are available to IGRP than to RIP, the basic configuration is every bit as simple The router command is used to establish the routing process, and the networkcommand is used to specify each network on which IGRP is to run. As with RIP, only major network numbers can be specified because IGRP is also a classful protocol. The commands neighbor, for sending unicast updates, and passive-interface, for preventing updates from being broadcast on selected...

Configuring OSPF

The many options and configuration variables available to OSPF frequently make it the IGP of choice in large IP internetworks. However, the opinion is occasionally expressed that OSPF configuration is too complex to be a good choice for small internets. This is nonsense. As the first case study shows, getting a basic OSPF configuration up and running involves only a few extra keystrokes in the network command if the operation of OSPF is reasonably well understood, these extra keystrokes will be...

Configuring Redistribution

Redistribution is configured in two steps 1. In the routing protocol configuration that is to receive the redistributed routes, use the redistribute command to specify the source of the routes. 2. Specify the metric to be assigned to the redistributed routes. For example, the IGRP configuration of Paige in Figure 11.14 is router igrp 1 redistribute ospf 1 metric 10000 100 255 1 1500 passive-interface Ethernet1 network 172.20.0.0 This configuration redistributes routes discovered by OSPF process...

Configuring Route Maps

Like access lists (see Appendix B,Tutorial Access Lists), route maps by themselves affect nothing they must be called by some command. The command will be either a policy routing command or a redistribution command. Policy routing will send packets to the route map, whereas redistribution will send routes to the route map. The case studies in this section demonstrate the use of route maps for both redistribution and policy routing. Route maps are identified by a name. For example, the following...

Contiguous network addresses

Ii 11111111 mi ti nium Hfiew HmMeiMtimtteiMMroMe 1 0000010 I i' i 0 00881 MO1W60008 1 f 0000010101 0001001 we BUD I 90000101 400001fiil 1M4BB0M 11 t4A aa 1 tooaaa 1 1q tmoeeM 11HHH1 1 I t*MH 1 1 i i inJS( W 11HHH1 141HHH10114W B0000 J1*eBO0010t l*Q0B001 111M6BB0M 91040000101 00000011 aa**MBBD0U --ffOOonKi H1WO0011 lii-if fiOi 11HtOO00101 (0000001181IWtflBDW 11 000010 Hi 00011 1S4M40DBM 11 HHeai 01 HHH111S14MBS0H i m eaiai *40 eaiii im& tiiM 11WOOB0101 ei oo00i 111 iMiHjuoiJi i .*iE.22.i i-1...

Corinths routing table shows that network 10000 is tagged as the default network

I R RTF, I' - mobile, 3- - 5GP D GFlP, EX - 1GRP extendi, 0 0 F, I A. OSPF JLilt i arta fi pspf external tvno i, f qsff external tvpe e > fo i is- s. Li - is- s level-, l2 IS-is ievei-2, - - canaitJ< ne dciauit Gatenay Of last resort is 172.16,3,1 to network 10.0.0,6 I* 10,0,-3,0 3 100.663 via 171.16.3.1, 00 00 17, Ethernet I ii2.i . .o 11W IW via iT2.te.31, ooicoiis, Ethernet I 172,16.6.0 180 17001 Via 172,1(5,3.1, r CO 13, EtIiarnfltO I 172.16.2,0 188 1290...

Counting to Infinity

Split horizon will break loops between neighbors, but it will not stop loops in a network such as the one in Figure 4.6. Again, 10.1.5.0 has failed. Router D sends the appropriate updates to its neighbors router C (the dashed arrows) and router B (the solid arrows). Router B marks the route via D as unreachable, but router A is advertising a next-best path to 10.1.5.0, which is 3 hops away. B posts that route in its route table. Figure 4.6. Split horizon will not prevent routing loops here....