How to Select Dynamic Routing on a Host That Is a Network Client

1. Become superuser on the host.

2. Ensure that the /etc/defaultrouter file is empty.

   If this file is empty, a network client is forced to select a dynamic routing protocol.

The type of dynamic routing used is selected by using the following criteria:

• If the /usr/sbin/in.rdisc program exists, the startup script starts in.rdisc. Any router on the network that is running RDISC then responds to any RDISC queries from the host. If at least one router responds, the host selects RDISC as its routing protocol.

• If the network router is not running RDISC or fails to respond to the RDISC queries, then in.rdisc on the host exits. The host then starts in.routed, which runs RIP.

How to Force a Machine to Be a Router

You can force a machine that has only one /etc/hostname.interface file (by default a host) to be a router.

1. Become superuser on the machine.

2. Create a file that is named /etc/gateways and leave this file empty.

This procedure is important if you decide to configure PPP links, as explained in System Administration Guide: Resource Management and Network Services.

Creating a Multihomed Host

By default, TCP/IP considers any machine with multiple network interfaces to be a router. However, you can change a router into a multihomed host--a machine with more than one network interface that does not run routing protocols or forward IP packets. You typically configure the following types of machines as multihomed hosts:

• NFS servers, particularly large data centers, can be attached to more than one network in order to share files among a large pool of users. These servers do not need to maintain routing tables.

• Database servers can have multiple network interfaces for the same reason as NFS servers--to provide resources to a large pool of users.

• Firewall gateways are machines that provide the connection between a company's network and public networks such as the Internet. Administrators set up firewalls as a security measure. When configured as a firewall, the host does not pass packets between the networks that are attached to the host. However, the host can still provide standard TCP/IP services, such as ftp or rlogin, to authorized users.

Because TCP/IP considers any machine with multiple network interfaces to be a router, you need to perform a few operations to turn the machine into a multihomed host.

How to Create a Multihomed Host

1. Become superuser on the prospective multihomed host.

2. Create an /etc/hostname.interface file for each additional network interface that is installed in the machine.

3. Type the following:

   % touch /etc/notrouter

   This command creates an empty file that is called /etc/notrouter.

4. Reboot the machine.

When the machine reboots, the startup script checks for the presence of the /etc/notrouter file. If the file exists, the startup script does not run in.routed -s or in.rdisc -r. The file also does not turn on IP forwarding on all interfaces that are configured "up" by ifconfig. This process happens regardless of whether an /etc/gateways file exists. Thus the machine is now a multihomed host.

Turning On Space-Saving Mode

Space-saving mode provides the host with a table that contains only the default routes. On a host, in.routed runs with space-saving mode turned off by default.

If the host is not to have a full routing table (which provides increased protection against misconfigured routers), turn space-saving mode on.

How to Turn On Space-Saving Mode

1. Become superuser on the host.

2. Edit the /etc/rc2.d/S69inet startup script by adding to the line /usr/sbin/in.routed -q the -s option:

   /usr/sbin/in.routed -q -s

   
   

   to

   /usr/sbin/in.routed -q -S

   
   

Turning Off ICMP Router Discovery

For reasons that involve router reliability, you might not want your hosts to use RDISC. If the automatic selection of RIP rather than RDISC by a host is to work reliably, the routers in the network (particularly those that run RDISC) must also work reliably.

If your routers are not running RDISC and you install a single Solaris router, by default all hosts that are connected to that router rely on that router alone. To have the hosts on that network use the other routers as well, turn off RDISC on the new router.

Turning Off ICMP Router Discovery Task Map

Table 4-5 Turning Off ICMP Router Discovery Task Map

How to Turn Off ICMP Router Discovery on the Host

1. Become superuser on the host.

2. Change the name of the host's /usr/sbin/in.rdisc to some other name, such as /usr/sbin/in.rdisc.saved.

3. Reboot the host.

How to Turn Off ICMP Router Discovery on the Router

1. Become superuser on the router.

2. Change the name of the router's /usr/bin/in.rdisc file to some other file name.

3. Reboot the router.

General Troubleshooting Tips

One of the first signs of trouble on the network is a loss of communications by one or more hosts. If a host refuses to come up at all the first time that the host is added to the network, the problem might be in one of the configuration files. The problem might also be a faulty network interface card. If a single host suddenly develops a problem, the network interface might be the cause. If the hosts on a network can communicate with each other but not with other networks, the problem could lie with the router, or the problem could be in another network.

You can use the ifconfig program to obtain information on network interfaces and netstat to display routing tables and protocol statistics. Third-party network diagnostic programs provide a number of troubleshooting utilities. Refer to third-party documentation for information.

Less obvious are the causes of problems that degrade performance on the network. For example, you can use tools such as ping to quantify problems such as the loss of packets by a host.