Chapter 9

Troubleshooting Network Problems (Tasks)

This chapter contains solutions for common problems that might occur on your network. The following topics are covered:

General Network Troubleshooting Tips

One of the first signs of trouble on a network is a loss of communications by one or more hosts. If a host does not 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 command to obtain information on network interfaces. Use the netstat command to display routing tables and protocol statistics. Third-party network diagnostic programs provide a number of troubleshooting tools. 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.

Running Basic Diagnostic Checks

If the network has problems, you can run a series of software checks to diagnose and fix basic, software-related problems.

How to Perform Basic Network Software Checking

On the local system, assume the Network Management role or become superuser.
Roles contain authorizations and privileged commands. For more information about roles, see "Configuring RBAC (Task Map)" in System Administration Guide: Security Services.

Use the netstat command to display network information.
For syntax and information about the netstat command, refer to Monitoring Network Status With the netstat Command and the netstat(1M) man page.

Check the hosts database to ensure that the entries are correct and current.
For information about the /etc/inet/hosts database, refer to hosts Database and the hosts(4) man page.

If you are running the Reverse Address Resolution Protocol (RARP), check the Ethernet addresses in the ethers database to ensure that the entries are correct and current.

Try to connect to the local host by using the telnet command.
For syntax and information about telnet, refer to the telnet(1) man page.

Ensure that the network daemon inetd is running.
# ps -ef | grep inetd

The following output verifies that the inetd daemon is running:
root 57 1 0 Apr 04 ? 3:19 /usr/sbin/inetd -s

If IPv6 is enabled on your network, verify that the IPv6 daemon in.ndpd is running:
# ps -ef | grep in.ndpd
The following output verifies that the in.ndpd daemon is running:
root 123 1 0 Oct 27 ? 0:03 /usr/lib/inet/in.ndpd

Common Problems When Deploying IPv6

This section describes issues and problems that you might encounter while planning and deploying IPv6 at your site. For actual planning tasks, refer to Chapter 4, Planning an IPv6 Network (Tasks).

IPv4 Router Cannot Be Upgraded to IPv6

If your existing equipment cannot be upgraded, you might have to purchase IPv6-ready equipment. Check the manufacturers' documentation for any equipment-specific procedures you might have to perform to support IPv6.

Certain IPv4 routers cannot be upgraded for IPv6 support. If this situation applies to your topology, physically wire an IPv6 router next to the IPv4 router. Then, you can tunnel from the IPv6 router over the IPv4 router. For tasks for configuring tunnels, refer to Tasks for Configuring Tunnels for IPv6 Support (Task Map).

Problems After Upgrading Services to IPv6

You might encounter the following situations when preparing services for IPv6 support:

Certain applications, even after they are ported to IPv6, do not turn on IPv6 support by default. You might have to configure these applications to turn on IPv6.
A server that runs multiple services, some of which are IPv4 only, and others that are both IPv4 and IPv6, can experience problems. Some clients might need to use both types of services, which leads to confusion on the server side.

Current ISP Does Not Support IPv6

If you want to deploy IPv6 but your current ISP does not offer IPv6 addressing, consider the following alternatives to changing ISPs:

Hire an ISP to provide a second line for IPv6 communications from your site. This solution is expensive.
Get a virtual ISP. A virtual ISP provides your site with IPv6 connectivity but no link. Instead, you create a tunnel from your site, over your IPv4 ISP, to the virtual ISP.
Use a 6to4 tunnel over your ISP to other IPv6 sites. For an address, use the registered IPv4 address of the 6to4 router as the public topology part of the IPv6 address.

Security Issues When Tunneling to a 6to4 Relay Router

By nature, a tunnel between a 6to4 router and a 6to4 relay router is insecure. Security problems, such as the following, are inherent in such a tunnel:

Though 6to4 relay routers do encapsulate and decapsulate packets, these routers do not check the data that is contained within the packets.
Address spoofing is a major issue on tunnels to a 6to4 relay router. For incoming traffic, the 6to4 router is unable to match the IPv4 address of the relay router with the IPv6 address of the source. Therefore, the address of the IPv6 host can easily be spoofed. The address of the 6to4 relay router can also be spoofed.
By default, no trust mechanism exists between 6to4 routers and 6to4 relay routers. Thus, a 6to4 router cannot identify whether the 6to4 relay router is to be trusted, or even if it is a legitimate 6to4 relay router. A trust relationship between the 6to4 site and the IPv6 destination must exist, or both sites leave themselves open to possible attacks.

These problems and other security issues that are inherent with 6to4 relay routers are explained in the Internet Draft, Security Considerations for 6to4. Generally, you should consider enabling support for 6to4 relay routers for the following reasons only:

Your 6to4 site intends to communicate with a private, trusted IPv6 network. For example, you might enable 6to4 relay router support on a campus network that consists of isolated 6to4 sites and native IPv6 sites.
Your 6to4 site has a compelling business reason to communicate with certain native IPv6 hosts.
You have implemented the checks and trust models that are suggested in the Internet Draft, Security Considerations for 6to4.