How to Diagnose Network Problems

If the PPP link becomes active but few hosts on the remote network are reachable, a network problem could be indicated. The following procedure shows you how to isolate and fix network problems that affect a PPP link.

1. Become superuser on the local machine or assume an equivalent role.

   Roles contain authorizations and privileged commands. For more information about roles, see Configuring RBAC (Task Map) in System Administration Guide: Security Services.

2. Shut down the problematic link.

3. Disable any optional protocols in the configuration files by adding the following options to your PPP configuration:

   noccp novj nopcomp noaccomp default-asyncmap

   These options provide the simplest uncompressed PPP that is available. Try to invoke these options as arguments to pppd on the command line. If you can reach the previously unreachable hosts, add the options in either of the following places.

   • /etc/ppp/peers/peer-name, after the call option

   • /etc/ppp/options, ensuring that the options apply globally

4. Call the remote peer. Then enable debugging features.

   % pppd debug call peer-name

5. Obtain verbose logs from the chat program by using the -v option of chat.

   For example, use the following format in any PPP configuration file:

   connect 'chat -v -f /etc/ppp/chatfile'

   /etc/ppp/chatfile represents the name of your chat file.

6. Try to re-create the problem by using Telnet or other applications to reach the remote hosts.

   Observe the debugging logs. If you still cannot reach remote hosts, the PPP problem might be network-related.

7. Verify that the IP addresses of the remote hosts are registered Internet addresses.

   Some organizations assign internal IP addresses that are known within the local network but cannot be routed to the Internet. If the remote hosts are within your company, you must set up a name-to-address translation (NAT) server or proxy server to reach the Internet. If the remote hosts are not within your company, you should report the problem to the remote organization.

8. Examine the routing tables.

   1. Check the routing tables on both the local machine and the peer.

   2. Check the routing tables for any routers that are in the path from the peer to the remote system. Also check the routing tables for any routers on the path back to the peer.

      Ensure that the intermediate routers have not been misconfigured. Often the problem can be found in the path back to the peer.

9. (Optional) If the machine is a router, check the optional features.

   # ndd -set /dev/ip ip_forwarding 1

   For more information about ndd, refer to the ndd(1M) man page.

   In the Solaris 10 release, you can use routeadm(1M), instead of ndd(1M).

   # routeadm -e ipv4-forwarding -u

   ---

   Note –

   The ndd command is not persistent. The values set with this command are lost when the system is rebooted. The routeadm command is persistent. The values set with this command are maintained after the system is rebooted.

   ---

10. Check the statistics that are obtained from netstat -s and similar tools.

    For complete details about netstat, refer to the netstat(1M) man page.

    1. Run statistics on the local machine.

    2. Call the peer.

    3. Observe the new statistics that are generated by netstat -s. For more information, refer to Common Network Problems That Affect PPP.

11. Check the DNS configuration.

    A faulty name service configuration causes applications to fail because IP addresses cannot be resolved.