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OpenSuSE 11.1 Quick Start Guide
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13.5 Network Problems

Many problems of your system may be network-related, even though they do not seem to be at first. For example, the reason for a system not allowing users to log in might be a network problem of some kind. This section introduces a simple check list you can apply to identify the cause of any network problem encountered.

When checking the network connection of your machine, proceed as follows:

  1. If using an ethernet connection, check the hardware first. Make sure that your network cable is properly plugged into your computer. The control lights next to your ethernet connector, if available, should both be active.

    If the connection fails, check whether your network cable works with another machine. If it does, your network card causes the failure. If hubs or switches are included in your network setup, suspect them to be the culprits as well.

  2. If using a wireless connection, check whether the wireless link can be established by other machines. If this is not the case, contact the wireless network's administrator.

  3. Once you have checked your basic network connectivity, try to find out which service is not responding. Gather the address information of all network servers needed in your setup. Either look them up in the appropriate YaST module or ask your system administrator. The following list gives some of the typical network servers involved in a setup together with the symptoms of an outage.

    DNS (Name Service)

    A broken or malfunctioning name service affects the network's functioning in many ways. If the local machine relies on any network servers for authentication and these servers cannot be found due to name resolution issues, users would not even be able to log in. Machines in the network managed by a broken name server would not be able to see each other and communicate.

    NTP (Time Service)

    A malfunctioning or completely broken NTP service could affect Kerberos authentication and X server functionality.

    NFS (File Service)

    If any application needed data stored in an NFS mounted directory, it would not be able to start or function properly if this service was down or misconfigured. In a worst case scenario, a user's personal desktop configuration would not come up if his home directory containing the .gconf or .kde subdirectories could not be found due to an outage of the NFS server.

    Samba (File Service)

    If any application needed data stored in a directory on a Samba server, it would not be able to start or function properly if this service was down.

    NIS (User Management)

    If your openSUSE system relied on a NIS server to provide the user data, users would not be able to log in to this machine if the NIS service was down.

    LDAP (User Management)

    If your openSUSE system relied on an LDAP server to provide the user data, users would not be able to log in to this machine if the LDAP service was down.

    Kerberos (Authentication)

    Authentication would not work and login to any machine would fail.

    CUPS (Network Printing)

    Users would not be able to print.

  4. Check whether the network servers are running and whether your network setup allows you to establish a connection:

    IMPORTANT: The debugging procedure described below only applies to a simple network server/client setup that does not involve any internal routing. It assumes both server and client are members of the same subnet without the need for additional routing.

    1. Use ping hostname (replace hostname with the hostname of the server) to check whether each one of them is up and responding to the network. If this command is successful, it tells you that the host you were looking for is up and running and that the name service for your network is configured correctly.

      If ping fails with destination host unreachable, either your system or the desired server is not properly configured or down. Check whether your system is reachable by running ping your_hostname from another machine. If you can reach your machine from another machine, it is the server that is not running at all or not configured correctly.

      If ping fails with unknown host, the name service is not configured correctly or the hostname used was incorrect. Use ping -n ipaddress to try to connect to this host without name service. If this is successful, check the spelling of the hostname and for a misconfigured name service in your network. For further checks on this matter, refer to Step 4.b. If ping still fails, either your network card is not configured correctly or your network hardware is faulty.

    2. Use host hostname to check whether the hostname of the server you are trying to connect to is properly translated into an IP address and vice versa. If this command returns the IP address of this host, the name service is up and running. If the host command fails, check all network configuration files relating to name and address resolution on your host:

      /etc/resolv.conf

      This file is used to keep track of the name server and domain you are currently using. It can be modified manually or automatically adjusted by YaST or DHCP. Automatic adjustment is preferable. However, make sure that this file has the following structure and all network addresses and domain names are correct:

      search fully_qualified_domain_name
      nameserver ipaddress_of_nameserver

      This file can contain more than one name server address, but at least one of them must be correct to provide name resolution to your host. If needed, adjust this file using the YaST DNS and Hostname module.

      If your network connection is handled via DHCP, enable DHCP to change hostname and name service information by selecting Change Hostname via DHCP and Update Name Servers and Search List via DHCP in the YaST DNS and Hostname module.

      /etc/nsswitch.conf

      This file tells Linux where to look for name service information. It should look like this:

       ...
      hosts: files dns
      networks: files dns
      ...

      The dns entry is vital. It tells Linux to use an external name server. Normally, these entries are automatically made by YaST, but it never hurts to check.

      If all the relevant entries on the host are correct, let your system administrator check the DNS server configuration for the correct zone information. For detailed information about DNS, refer to Section 22.0, The Domain Name System, (↑ Reference ). If you have made sure that the DNS configuration of your host and the DNS server are correct, proceed with checking the configuration of your network and network device.

    3. If your system cannot establish a connection to a network server and you have excluded name service problems from the list of possible culprits, check the configuration of your network card.

      Use the command ifconfig network_device (executed as root) to check whether this device was properly configured. Make sure that both inet address and Mask are configured correctly. An error in the IP address or a missing bit in your network mask would render your network configuration unusable. If necessary, perform this check on the server as well.

    4. If the name service and network hardware are properly configured and running, but some external network connections still get long time-outs or fail entirely, use traceroute fully_qualified_domain_name (executed as root) to track the network route these requests are taking. This command lists any gateway (hop) a request from your machine passes on its way to its destination. It lists the response time of each hop and whether this hop is reachable at all. Use a combination of traceroute and ping to track down the culprit and let the administrators know.

Once you have identified the cause of your network trouble, you can resolve it yourself (if the problem is located on your machine) or let the system administrators of your network know about your findings so they can reconfigure the services or repair the necessary systems.

13.5.1 NetworkManager Problems

If you have a problem with network connectivity, narrow it down as described in . If NetworkManager seems to be the culprit, proceed as follows to get logs providing hints on why NetworkManager fails:

  1. Open a shell and log in as root.

  2. Restart the NetworkManager:

    rcnetwork restart -o nm
  3. Open a web page, for example, http://www.opensuse.org as normal user to see, if you can connect.

  4. Collect any information about the state of NetworkManager in /var/log/NetworkManager.

For more information about NetworkManager, refer to Section 10.0, Using NetworkManager.

OpenSuSE 11.1 Quick Start Guide
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