Chapter 5 - Planning for Routing Through TCP/IP
Your primary routing management task is to build and maintain a routing table on your server. The routing table is the part of the TCP/IP configuration that contains routing entries, which specify how destinations in the network are reached. Entries are created automatically by the TCP/IP configuration program, or manually by means of the Manage Routing through TCP/IP function of the configuration program.
The following routing management functions require you to create and maintain routing entries:
Specify/Change Default Gateway - Allows you to create an entry for the default gateway.
Manage Specific Routes - Allows you to create entries manually that define routes through gateways.
Manage Adjacent Networks - Allows you to create entries manually that define direct routes to networks or subnetworks.
The ways in which routing entries are created are described in the next two sections, followed by sections that describe how to plan for managing routing.
Creating Routing Entries Automatically
The TCP/IP configuration program can automatically set up routes to destinations, using the following information:
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The network numbers in the IP addresses of other servers in your VINES network. ![]()
The network and subnetwork numbers in the IP addresses of interfaces. If you assign an IP address to the VINES interface, the network and subnetwork numbers in the address are used to create a direct route to all the PCs running PC/TCP that have those numbers in their IP addresses. The PCs must run the PC/TCP VINES Transport version, which enables them to use the routing services of a server from anywhere in the server's VINES network. They must configure this server as their default gateway. Refer to your PC/TCP documentation for instructions.
However, the routes that are created automatically are not useful if the IP addresses of the servers or interfaces are not correctly specified. In this case, you must either create new routes manually or change the IP addresses of the servers or interfaces.
Chapter 6 and Chapter 8 describe how to specify IP addresses of servers and interfaces, respectively.
Figure 5-1 shows all the IP addresses that Server 1 knows about, including those assigned to its own interfaces and to other servers.
The network manager of Server 1 specified the IP addresses of interfaces and servers correctly. The route entries that the TCP/IP configuration program created automatically from this information are shown below. Eight bits of subnetwork mask are assumed for each address.
As another example, Figure 5-2 shows Server 1's knowledge of the network, based in part on an IP address that should not have been assigned.
The network manager included incorrect network and subnetwork numbers in the IP address of Server 1's Ethernet interface. The route created to network 125.125.3 will not reach any of the hosts in the network. The useless route entry the TCP/IP configuration program created using this address is shown below.
Notice that no direct route is defined to 160.134, which is the subnetwork number found in Foreign Host 3's IP address, and Server 3's IP address on Ethernet. Server 1 cannot route IP packets to either Foreign Host 3 or Server 3.
Record all the routing entries that can be created automatically on the Routing Information Worksheet. Use the following numbers to help you:
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The network numbers in the IP addresses of other servers. Obtain these numbers from the TCP/IP Server Information Worksheet. ![]()
The network and subnetwork numbers in the IP addresses you assign to interfaces. Obtain these numbers from the IP Interfaces Worksheet.
If the network or subnetwork number in the IP address of an interface on your server differs from those of other hosts on the segment attached to the interface, do not use it. See "Planning for Managing Adjacent Networks" later in this chapter for more information.
Creating Routing Entries Manually
The TCP/IP configuration program may not be able to define automatically all the routes that your server needs to know. You may have to create some routing entries yourself.
For example, the TCP/IP configuration program on Server 1 in Figure 5-1 cannot create a route to network 140.122, forcing the system manager of Server 1 to create the following entry:
It is assumed that Foreign Host 1 (130.133.1.2) knows how to route IP packets to network 140.122.
Server 1 can also reach 140.122 if Foreign Host 1 is specified as the default gateway. The next section, "Default Gateway Planning," provides more information.
You create routing entries manually when you specify the default gateway, manage specific routes, or manage adjacent networks. The sections that follow help you plan for performing these functions.
You are not required to specify a default gateway. However, doing so can eliminate the need to define several routes to various destinations.
For example, if you are building the routing table for Server 1 in Figure 5-3, you do not have to define specific routes to networks 140.134 and 150.111. You specify Foreign Host Gateway 1 as the default gateway, which is expected to route packets to 140.134 and 150.111.
Using the TCP/IP configuration program, you would specify the IP address of Foreign Host Gateway 1 as follows:
130.135.1.1
Your choice of default gateway depends on which option your server has installed, as explained in the next two sections.
Default Gateways for Servers with the Routing Option
A server equipped with the Routing option probably has to reach many destinations outside its VINES network. When you specify a default gateway, you should select the gateway that allows you to reach the most IP destinations. By specifying the appropriate default gateway for your server, you can avoid the need to define specific routes to all of these destinations. You can specify as the default gateway either another server with the Routing option installed, or a foreign host gateway.
You should define specific routes to destinations that cannot be reached either through the default gateway or through routes created automatically. See "Planning for Managing Specific Routes" later in this chapter.
Record the IP addresses for your server on the Routing Information Worksheet, explained in "Filling Out the Routing Information Worksheet" later in this chapter.
Default Gateways for Servers with the Server-to-Server Option
If your server has the Server-to-Server option installed, you should specify a foreign host gateway as the default gateway. If your server is connected to multiple foreign host gateways, specify the one that will handle the largest amount of traffic from your server.
Planning for Managing Specific Routes
In many cases, the route entries created automatically and the default gateway provide all the routing knowledge your server needs. However, the TCP/IP configuration program cannot always create entries for all the routes your server needs to know. You may have to create entries manually for specific routes.
Find out if you need to define specific routes. If you do, identify the routes you need to define.
In Figure 5-4, the network manager for Server 1 has specified Foreign Host 1 as the default gateway. (See Chapter 9 for specific instructions.) The network manager need not create routes in the routing table for Server 1. Automatically created entries and the entry for the default gateway provide all the necessary routing knowledge. The routing table for Server 1 is shown here.
Suppose that Server 1 is part of a more complex topology, as shown in Figure 5-5. In this case, Foreign Host Gateway 3 is used as the default gateway, because more destinations can be reached through it than through any other gateway. All routes to destinations inside Server 1's VINES network and network 145.179 can be defined automatically. However, Server 1's network manager must create an entry that defines a route to network 147.190. (This example assumes that no subnetworking is used.)
Server 1's routing table for the complex topology is as follows:
When you identify routes that need to be defined manually, make sure that you meet the routing needs of the particular TCP/IP option installed on your server.
If your server has the Server-to-Server option installed, make sure that your server can reach all the servers outside your VINES network that have that option installed. This involves defining routes to the IP networks in which these servers reside. For example, Server 1 in Figure 5-4 can reach Server 2's IP network (140.122) through Foreign Host 1, the default gateway.
If your server has the Routing option installed, make sure that your server can reach all the appropriate destination IP networks, subnetworks, and hosts.
Servers equipped with the Routing option also should know all the other servers that have that option and reside in the same VINES network. For example, assume that Server 4 in Figure 5-6 has the Routing option installed. Server 1 should know that it can reach network 134.148 through Server 4.
The route to 134.148 is specified in Server 1's routing table as follows:
Record all the route entries that you have to enter manually on the Routing Information Worksheet. The section "Filling Out the Routing Information Worksheet" later in this chapter provides information.
Planning for Managing Adjacent Networks
Networks or subnetworks that share the same LAN segment are connected directly to each other. You should not have to manage networks or subnetworks of this type if you correctly set up the IP addresses of your server's network interfaces. Chapter 4 provides information on assigning IP addresses to LAN interfaces.
However, if you cannot correctly set the IP addresses of LAN interfaces, your server and the other hosts on those LANs will be in different networks or subnetworks.
When your server and other hosts on a LAN segment reside in different networks, the network number in the IP address of your server's LAN interface differs from the network numbers in the IP addresses of the other hosts. Similarly, when your server and other hosts on a LAN segment reside in different subnetworks, the subnetwork number in the IP address of your server's LAN interface differs from the subnetwork numbers in the IP addresses of the other hosts.
For example, if your server were the one in Figure 5-7, you would use the TCP/IP configuration program to define a route to network 160.134.
Likewise, if your server were the one in Figure 5-8, you would use the TCP/IP configuration program to define a route to subnetwork 135.126.2.
To plan for adjacent networks or subnetworks, follow these steps:
1. Using the IP Interfaces Worksheet, look at the IP address you plan to assign to each LAN interface on your server.
2. For each LAN interface, compare the network and subnetwork numbers in the IP address to the corresponding numbers in the IP addresses of the other hosts on the LAN segment. If the numbers are different, then proceed to step 3. If the numbers are the same, you do not have to manage adjacent networks.
3. Record the appropriate network and subnetwork numbers on the Adjacent Networks Worksheet. The section "Filling Out the Adjacent Networks Worksheet" later in this chapter provides information.
Defining Routes to Specific Hosts
In some situations, you may want to define a route to a single host to regulate traffic. For example the network manager responsible for Server 3 in Figure 5-9 anticipates a heavy volume of traffic between Server 3 and Foreign Host 1.
Server 3 usually routes traffic through Server 1 by specifying it as the default gateway. However, because of the heavy volume of traffic that already passes through Server 1, the network manager decides to set up a route for traffic between Server 3 and Foreign Host 3.
Server 3 uses Foreign Host 3 as a gateway only for traffic destined for Foreign Host 1. For example, when Server 3 has to route traffic to Foreign Host 2, it will do so through Server 1. The purpose of the route between Server 3 and Foreign Host 3 is to handle traffic destined for Foreign Host 1, and to handle traffic originating from Foreign Host 1 that is destined for Foreign Host 4 and the PC running PC/TCP.
The entry for Foreign Host 1 in Server 3's routing table appears as follows:
Filling Out the Routing Information Worksheet
On the Routing Information Worksheet, record the route entries that will appear in the routing table on your server. You will need this information for the task of managing routing through TCP/IP, as explained in Chapter 9.
For each interface, record the following information on the Routing Information Worksheet:
Worksheet for Server - The name of your server.
Default Gateway - The IP address of the default gateway. If the default gateway is a VINES server accessible only across a VINES network, specify the server's name.
Interface Name - The name of each interface that IP will use. Use descriptive names such as Eth1 for an Ethernet interface or Pro1 for a ProNET-10 interface. Do not forget the interface to VINES if your server and other servers in your VINES network have the Routing option installed. You also need to consider the interface to VINES if workstations running PC/TCP will use your server as a gateway.
IP Address - Specify the address of each IP interface.
Gateways - Specify the IP address of each gateway on the interface. Write "Direct" for entries for direct routes.
Destinations - Write the IP address of each destination next to the IP address of the gateway your server uses to reach it.
Subnetwork Mask - If the destination is a network or subnetwork, write its subnetwork mask.
Type - Specify the type of destination: network, subnetwork, or host.
Auto or Manual? - Specify whether the route can be automatically created (Auto), or whether you must create it (Manual).
Sample Routing Information Worksheets for Server 1 in Figure 5-5 are shown in Figure 5-10 and Figure 5-11.
Filling Out the Adjacent Networks Worksheet
On the Adjacent Networks Worksheet, record the network and subnetwork numbers of directly connected networks and subnetworks. You need the worksheet when you use the TCP/IP configuration program to manage adjacent networks and subnetworks, as explained in Chapter 9. Record the following information:
Worksheet for Server - The name of your server.
Interface Name - The name of each IP interface to a LAN segment that connects your server to hosts with different network or subnetwork numbers in their IP addresses.
IP Address - The IP address of each IP interface.
Destinations - The IP address of each destination network or subnetwork on each LAN segment.
Subnetwork Mask - The subnetwork mask to be used for each destination IP address.
A sample Adjacent Networks Worksheet for Your Server in Figure 5-7 is shown in Figure 5-12.