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566 Chapter 11 • Troubleshooting Windows 2000 Connectivity Problems at the Internetwork Level networks (such as ATM or X.25). OSPF has different protocols for broad- cast and multicast network types. OSPF uses the Dijkstra algorithm, which comes from the branch of mathematics known as graph theory, to calculate the lowest-cost path to a destination from a given source. OSPF on a Broadcast Network On a broadcast network, OSPF uses a packet called a Hello protocol mes- sage, which is a broadcast message by which routers locate one another. A router is selected to be the Designated Router (DR), and all the other routers exchange routing information with the DR. Then, the DR updates neighboring routers. The DR is elected by an exchange of Hello packets. Each packet includes the current DR, the sending router’s router ID, and its router priority (which can be set during configuration of OSPF). The router with the highest priority is selected to be the DR. If more than one router has the same priority, the one that has the highest router ID will become the DR. A backup DR is also elected for multiaccess networks, so if the DR becomes unavailable, connectivity will not be lost. Configuring an OSPF router with a priority of 0 means it cannot become a DR. There must be at least one router on the multiaccess network that has a priority of 1 or above. Otherwise, no router can become DR and the link state database cannot be synchronized, resulting in no traffic being passed across that network. OSPF on a Nonbroadcast Network On a network using a nonbroadcast architecture, such as ATM, OSPF has to be initially configured manually with the addresses of neighboring routers. A DR is also used, but rather than sending the routing informa- tion via broadcast or multicast, it is sent point to point, between the DR and the other routers. This means a greater number of virtual NOTE WARNING 91_tcpip_11.qx 2/25/00 11:17 AM Page 566 Troubleshooting Windows 2000 Connectivity Problems at the Internetwork Level • Chapter 11 567 connections are required for complete connectivity, making it more com- plex and more resource-intensive than a broadcast network implementa- tion. OSPF on a Point-to-Point Network OSPF can also be used on a dedicated point-to-point network such as T-1 leased lines, connecting only two routers. IP multicast addresses are used for the OSPF messages. OSPF’s Hierarchical Routing Structure The routing tables used by a distance vector protocol like RIP have a flat structure, and every RIP router on the internetwork must contain an entry for every network. The networks are not divided into areas or groups; all are seen as individual entities—thus the “flat” description. Link state protocols like OSPF create a hierarchical structure by dividing the internetwork into areas. Every OSPF router belongs to an area, identi- fied by a 32-bit number, expressed in dotted decimal called the area num- ber. This greatly reduces the size of the routing table for each router, since it only has to keep entries for its area. Although the area address is in the same format as an IP address, it is an entirely different number, assigned by the administrator. It has no relationship to the network ID, although if the networks in an area are all in one subnetted network ID, you could, for convenience, use the network ID as the Area ID. Windows 2000 allows you to configure up to 16 areas for an interface. There is also a backbone area designated as area 0.0.0.0. The router that connects an area to the backbone area is called an Area Border Router (ABR). This router is a member of its area and contains routing information for that area, but also is a member of area 0.0.0.0 and can route between the two areas. See Figure 11.12 for an illustration of this. The ABR has a separate link state database for each area to which it belongs, and SPF calculations are performed independently for each area. NOTE 91_tcpip_11.qx 2/25/00 11:17 AM Page 567 568 Chapter 11 • Troubleshooting Windows 2000 Connectivity Problems at the Internetwork Level OSPF Areas An area can consist of one or more networks or subnets. The advantage of splitting the internetwork into areas is that you reduce the bandwidth used for routing so that it is proportionate to the size of the area rather than the size of the internetwork as a whole. ABRs can summarize the routes within their areas. Route summariza- tion means that each ABR communicates a single route for its area to the backbone router. Thus, the Area 0.0.0.0 routing table contains only the number of routes that correspond to the number of areas, rather than all routes for each area. In Figure 11.12, Area 0.0.0.0’s database would be required to contain only four routes, regardless of how many routers and routes exist within each of the four areas. Route summarization also decreases recalculations of routes. Whenever a network is added or removed, each OSPF router must recal- culate the database. By using areas, if a new network is added to Area 0.0.1.1, the routers in other areas will not be required to recalculate since the summarized route is still valid. Figure 11.12 The hierarchical structure of OSPF routing architecture. Area 0.0.1.1 Area 0.0 0.1 Area 0.0.1.0 Area 0.1.0.0 Area 0.0.0.0 (The backbone area) ABRRouter ABR ABR ABR Router Router Router Router Router Router Router Router Router Router Router 91_tcpip_11.qx 2/25/00 11:17 AM Page 568 Troubleshooting Windows 2000 Connectivity Problems at the Internetwork Level • Chapter 11 569 OSPF Router Classifications OSPF routers on the internetwork are designed as one of the following: ■ ABR Area Border Router (routes between the area to which it belongs and the backbone area). ■ IR Internal Router (routes within its area). ■ BR Backbone Router (Area 0.0.0.0 router). ■ ASBR Autonomous System Border Router (used on global internetworks, such as the Internet, to add another layer of the hierarchy. An Autonomous System, or AS, represents an entire enterprise network within the global internetwork). AS numbers are allocated by the Internet Assigned Numbers Authority (IANA), as they must be globally-unique. OSPF uses 32-bit router identification numbers (router IDs) rather than the routers’ IP addresses to keep track of individual routers on the internetwork. This is because each router will have more than one IP address. The administrator assigns the router ID. It is common practice, although in no way required, to use the router’s lowest IP address for its router ID. The Protocols Used by OSPF The following protocols are used within OSPF: Common header protocol. The common header used for OSPF messages includes the version number, type, packet length, the router ID, Area ID, a checksum, and an authentication field (messages can be sent with password authentication or no authentication). Hello protocol. The Hello protocol is used on broadcast networks to discover the identities and routes of neighboring routers. NOTE TIP 91_tcpip_11.qx 2/25/00 11:17 AM Page 569 570 Chapter 11 • Troubleshooting Windows 2000 Connectivity Problems at the Internetwork Level Exchange protocol. The Exchange protocol uses database description packets in a master-slave relationship. The master sends the database description packets, and the slave sends an acknowledgment. Flooding protocol. The Flooding protocol is used when a link changes state, as when the link between two routers goes down. The router that is responsible for the changed link issues the new link state information, and the updated information is sent in regular intervals until an acknowledgment is received. Aging Link State Records protocol. The Aging Link State Records protocol is used to remove old, outdated records from the database. When the record is originally issued, its age is set as 0. It is incremented by 1 every second and on each hop, and when its age matches the designated maximum, the router removes it and informs neighboring routers of the change. Advantages of OSPF Despite the fact that it is much more complex and requires more techni- cal expertise to implement properly, OSPF has many advantages over RIP and other distance vector protocols: ■ More efficient calculation of routes ■ Faster convergence ■ Support for load balancing ■ Low bandwidth utilization ■ No routing loops or count-to-infinity problems ■ Hierarchical structure isolates instability within an area ■ More scalability, appropriate for larger networks ■ Secure password authenticated transmission of update messages Windows 2000 as an IP Router A Windows 2000 multihomed host computer is configured as an IP router to provide packet forwarding for other TCP/IP computers by enabling the RRAS service and setting up a routed IP network. This can be a static routed network, a RIP for IP routed internetwork, or an OSPF routed internetwork. For more information about installing RRAS, see Chapter 9, “Troubleshooting Remote Access in a Windows 2000 TCP/IP Network.” The Windows 2000 router supports both RIP (versions 1 and 2) and OSPF dynamic routing protocols. 91_tcpip_11.qx 2/25/00 11:17 AM Page 570 Troubleshooting Windows 2000 Connectivity Problems at the Internetwork Level • Chapter 11 571 Installing Routing Protocols The Windows 2000 router supports dynamic routing, using RIP or OSPF. To install the RIP or OSPF protocol, open the RRAS management console. In the left console pane, expand the name of the RRAS server, expand IP Routing, and right-click General. Select New Routing Protocol, as shown in Figure 11.13. Figure 11.13 Adding a dynamic routing protocol to the Windows 2000 router. You will be given a choice to select either RIP or OSPF. Make the appropriate choice, and the protocol will be added. You can now configure it by right-clicking on its name, which will show up in the left console pane under IP Routing. 91_tcpip_11.qx 2/25/00 11:17 AM Page 571 572 Chapter 11 • Troubleshooting Windows 2000 Connectivity Problems at the Internetwork Level Windows 2000 Router Management Tools Windows 2000 provides built-in router management tools for the adminis- tration of the static, RIP, or OSPF router. A Windows 2000 router can be administered locally or remotely from another Windows 2000 computer running RRAS. Remote Router Administration Windows 2000 allows you to administer a remote Windows 2000 router via the RRAS management console. To do so, open the RRAS MMC, and in the left pane of the console tree, right-click Server Status, then Add Server. A dialog box as shown in Figure 11.14 will appear. Figure 11.14 Use the Add Server dialog box to select the computer(s) to administer remotely. As you can see, you can select “The following computer:” and type in the name of the Windows 2000 router computer, you can select to admin- ister all RRAS computers in a designated domain, or you can browse the Active Directory to find the computer to be administered. If you choose to browse the Directory, you will see a dialog box like the one displayed in Figure 11.15. If you elect to administer all RRAS servers in the domain, the names of all Windows 2000 computers in the domain running RRAS will be dis- played in the left console of the MMC, as shown in Figure 11.16. You may notice in Figure 11.16 that there are three Windows 2000 computers running RRAS in the tacteam domain. One of them, DS2000, is marked with a red and white “X” to indicate that this computer is not a router or RRAS server and cannot be administered remotely (DS2000 is a Windows 2000 Professional workstation). 91_tcpip_11.qx 2/25/00 11:17 AM Page 572 Troubleshooting Windows 2000 Connectivity Problems at the Internetwork Level • Chapter 11 573 You can now add new interfaces and routing protocols, and manage the routing components on the remote Windows 2000 router computer just as you could locally. Figure 11.15 You can browse the Directory to find Windows 2000 routers or RAS servers. Figure 11.16 Windows 2000 RRAS computers that can be remotely administered are displayed. 91_tcpip_11.qx 2/25/00 11:17 AM Page 573 574 Chapter 11 • Troubleshooting Windows 2000 Connectivity Problems at the Internetwork Level Using ICMP Router Discovery You can use the Internet Control Message Protocol (ICMP), a TCP/IP utili- ty, to configure IP host computers with the IP addresses of local routers (and establish a method for the hosts to detect that a router is down). To do so, implement router solicitation and advertisement. ICMP router discovery messages are discussed in RFC 1256. Here’s how it works: 1. Host computers send router solicitation messages to discover the routers on their networks. 2. Routers send router advertisement messages in response to the solicitations. The routers also send advertisements on a regular basis (unsolicited) to inform the host computers that the routers are still up and available. To enable ICMP router discovery, open the RRAS console, and in the left pane of the console tree, under the Windows 2000 router on which you wish to enable discovery messages, click General under IP Routing. In the right console pane, right-click the name of the router interface you wish to enable for ICMP, then click Properties. Select the General tab, as shown in Figure 11.17, and check the “Enable router discovery advertise- ments” check box. Here, you can set the lifetime of the advertisement (the time after which a router will be considered to be down or unavailable) in minutes. You can also set the minimum and maximum rates for sending of ICMP advertisements by the router. “Level of preference” refers to the level of preference for this Windows 2000 router to be the default gateway for host computers on the network. Using the Netshell Utility (NETSH) NETSH is a command-line utility included with Windows 2000, with which you can configure routes, interfaces, and routing protocols on Windows 2000 RRAS routers. The NETSH utility will allow you to display the configuration of routers that are running on Windows 2000 RRAS computers, and supports scripting so that you can run commands as batch files for a particular router. NOTE 91_tcpip_11.qx 2/25/00 11:17 AM Page 574 Troubleshooting Windows 2000 Connectivity Problems at the Internetwork Level • Chapter 11 575 NETSH is used for management of other services, such as DHCP and WINS. To change the NETSH context to routing, use the routing com- mand within NETSH, as shown in Figure 11.18. Figure 11.17 Enabling router discovery advertisement messages. Figure 11.18 Use the NETSH command to display routing information. 91_tcpip_11.qx 2/25/00 11:17 AM Page 575 [...]... a specified list External route filters can only be used for filtering of routes that come from nonOSPF sources 91 _tcpip_11.qx 2/25/00 11:17 AM Page 598 91 _tcpip_12.qx 2/25/00 11: 19 AM Page 599 Chapter 12 Troubleshooting Selected Services on a Windows 2000 TCP/IP Network Solutions in this chapter: s IIS Services s FTP Services 599 91 _tcpip_12.qx 2/25/00 11: 19 AM Page 600 600 Chapter 12 • Troubleshooting... run in a separate process or in the same process as IIS IIS 5: You can group applications together into pooled processes to increase performance By default, Web services run in a separate process, and other applications run in a pooled process Continued 91 _tcpip_12.qx 2/25/00 11: 19 AM Page 601 Troubleshooting Selected Services on a Windows 2000 TCP/IP Network • Chapter 12 601 Feature or Procedure Changes... can capture the RIPv2 announcements and view the password 91 _tcpip_11.qx 2/25/00 11:17 AM Page 590 590 Chapter 11 • Troubleshooting Windows 2000 Connectivity Problems at the Internetwork Level Troubleshooting OSPF OSPF routing problems are often caused by improper configuration preventing adjacencies from forming properly Adjacencies are the relationships between adjacent OSPF routers When the protocol... interface ? Displays help Standard TCP/IP tools, such as PING, TRACERT, and PATHPING, are the common starting point for troubleshooting an IP routing problem See Chapter 4, Windows 2000 TCP/IP Internals,” for more information on how to use these command-line utilities Router Configuration Proper configuration of the router(s) will prevent many problems Configuring Windows 2000 as an IP router, for either... into the Windows 2000 RIP implementation that help to prevent problems such as routing loops These include 91 _tcpip_11.qx 2/25/00 11:17 AM Page 593 Troubleshooting Windows 2000 Connectivity Problems at the Internetwork Level • Chapter 11 593 the split horizon and poison reverse algorithms, along with the use of triggered updates for situations where three or more gateways are involved (and thus split horizon... The OSPF Interface Properties dialog box appears in Figure 11.22 91 _tcpip_11.qx 2/25/00 11:17 AM Page 583 Troubleshooting Windows 2000 Connectivity Problems at the Internetwork Level • Chapter 11 583 Figure 11.22 The OSPF Interface dialog box showing the contents of the General tab OSPF Password Protection All OSPF routers in the Area must use the same password To set the password, click OSPF in the... and default routes (which are not propagated by default) will be propagated on the network 91 _tcpip_11.qx 2/25/00 11:17 AM Page 595 Troubleshooting Windows 2000 Connectivity Problems at the Internetwork Level • Chapter 11 595 We discussed password protection of update information on OSPF routers, learning that all OSPF routers on the internetwork must use the same password, and that it is case-sensitive... Troubleshooting Selected Services on a Windows 2000 TCP/IP Network Introduction In this book, we’ve examined how TCP/IP connectivity works, and addressed some of the problems that can occur with Windows 2000 computers using the TCP/IP protocol We’ve looked at general network connectivity problems such as IP addressing problems, NetBIOS name resolution problems, and DNS/DDNS problems We then discussed services... so the port and the device will be the seen as one entity With multiport devices, like a modem bank or a two-channel ISDN terminal adapter, each point-topoint connection occurs over a separate port 91 _tcpip_11.qx 2/25/00 11:17 AM Page 597 Troubleshooting Windows 2000 Connectivity Problems at the Internetwork Level • Chapter 11 597 Q: How do you prevent invalid routes from external sources (RIP routes... 2000 Connectivity Problems at the Internetwork Level Troubleshooting RIP for IP Testing and troubleshooting a RIP network can be done using tools that are built into Windows 2000 Proper planning and multiphased deployment that includes testing of each added feature will make problem isolation and solutions easier Viewing RIP Neighbors The ability to view the Windows 2000 router’s RIP neighbors is useful . see Chapter 9, “Troubleshooting Remote Access in a Windows 2000 TCP/IP Network.” The Windows 2000 router supports both RIP (versions 1 and 2) and OSPF dynamic routing protocols. 91 _tcpip_11.qx. script igmp Changes to 'routing ip igmp' context nat Changes to 'routing ip nat' context ospf Changes to 'routing ip ospf' context relay Changes to 'routing ip. done: 91 _tcpip_11.qx 2/25/00 11:17 AM Page 576 Troubleshooting Windows 2000 Connectivity Problems at the Internetwork Level • Chapter 11 577 ■ Install the proper hardware (the Windows 2000 computer