Common Problems

This section discusses the following common problems and their potential solutions:

• LAN Connectivity Problems
• Router Cannot Ping a Remote Router or the Internet
• Routing Table Maintenance Problems
• IP Address Duplication across Machines
• Server Not Responding under Heavy Stress Conditions
• Server Not Responding under Heavy Stress Conditions
• Load Not Balanced across NICs although LB is enabled in INETCFG
• Network Traffic Is Not Balanced across NICs
• Losing INETCFG Configuration Information upon Rebooting
• Loss of Secondary IP Address upon Deleting Any Binding

LAN Connectivity Problems

• The router does not forward IP packets

  Verify that the IP Packet Forwarding statistic is set to Router Enabled in TCPCON (Protocols > IP). If routing is not enabled, enable IP Packet Forwarding under Protocols in INETCFG, and then issue the REINITIALIZE SYSTEM command.

• A TCP/IP host cannot reach the router on the local network
  • Verify that the network portion of the IP address and the subnet mask are the same on the router and the host.
  • Verify that the router and host use the same frame type.
  • Use PING from the router to verify connectivity to the
    TCP/IP host and verify that the IP Address Translation table has an entry for the host.

    If there is no entry, use MONITOR to check the status of the LAN driver.

  • Use PING from the router to verify connectivity to the
    TCP/IP host and check for Echo Requests in TCPCON (select Statistics > ICMP).

    If the value of the Echo Requests statistic is not incrementing, check the IP statistics for errors and perform Step 7 in Troubleshooting Checkpoints.

  • Use PING from the router to verify connectivity to the
    TCP/IP host and check for Echo Replies in TCPCON (select Statistics > ICMP).

    If the value of the Echo Replies statistic is not incrementing, verify that IP is bound to the host's interface with the correct address and mask. Also, verify that the interface driver is loaded with the correct frame type. If required, check the IP statistics for errors and perform Step 7 in Troubleshooting Checkpoints.

• A TCP/IP host cannot reach a remote host
  • Verify that the IP address and mask are proper.
  • Verify that the local TCP/IP host has the local router listed as the default router.
  • Verify that each router has a routing protocol enabled and that it has not been disabled on the interface.
  • Starting at the local router, verify that each router has a route to the remote host's network.
  • Verify that there are no filters capable of blocking IP traffic configured on any routers along the path.
  • Verify that the remote host has a route to the local host's network.
  • Using PING, verify that the remote host can reach each router on the path to the local TCP/IP host.
  • Starting at the router closest to the remote host, verify that each router has a route to the local TCP/IP host's network.

• The router cannot initiate IP traffic to a remote router through a LAN interface
  • Verify that IP is bound to the right interface with the correct address and mask.
  • Check whether the interface driver is loaded with the correct frame type.
  • Check whether a route exists to the network on which the destination router resides. This can be done through the IP Routing Table window of TCPCON. If the destination router is accessible, also verify that it has a route to the source router's network.

• A TCP/IP host cannot reach another host when Fault Tolerance is disabled and the NIC that was handling the data transfer has gone down
  • Make sure the NIC is grouped for load balancing and fault tolerance.
  • Make sure that fault tolerance is enabled for the group.

To verify that NIC is grouped, do the following:

1. Load INETCFG and select Bindings > TCP/IP.

2. Select Configure TCP/IP Bind Option.

3. Make sure that the Group interface for LBFT is set to Yes.

To check that fault tolerance is enabled, do the following:

1. Load INETCFG and select Protocols > TCP/IP.

2. In the screen that appears, fault tolerance should be enabled.

   This could be for the complete system. You still need to verify whether Fault Tolerance is enabled for the particular Net Group.

3. Select Fault Tolerance Configuration > Configure Individual Group.

4. Select the particular Net Group and check whether fault tolerance is enabled for it. If not, set it to Yes.

Router Cannot Ping a Remote Router or the Internet

Load TCPCON and verify select IP Routing Table that there is a destination that is specified as the default route. If there is no default route, you must configure it. Load INETCFG to permanently configure the default route.

1. Load INETCFG and select Bindings > TCP/IP.

2. Select the Interface Group for your WAN card.

3. Select WAN Call Destination.

4. Select WAN Call Destination press Ins and then select the WAN card defined earlier.

5. Select Static Routing Table option and press Ins.

   The Static Routing entry sets up the default route that points to the Internet Service Provider (ISP).

6. Select Route to Network or Host > Default Route.

7. Press Esc to save your changes and exit the menus.

8. For the changes to take effect, reinitialize the system.

Routing Table Maintenance Problems

• Routes are not exchanged on a LAN.
  • Use INETCFG to verify that the IP Packet Forwarding option is enabled.
  • Use INETCFG to verify that a routing protocol has been enabled.
  • Use INETCFG to verify that the routing protocol has not been disabled on an interface.
  • Use TCPCON to examine the routing table and determine which routes are missing.
  • Check TCPCON for IP errors.
  • Check TCPCON for ICMP errors.
  • If you are using RIP, then in INETCFG under Bindings, verify that the RIP Mode option is not set to Send Only or Receive Only.
  • If the RIP Version option is set to RIPII, verify that the other routers also support RIP II.
  • Verify that no route filters are configured that would block route information packets for that interface.
  • If you are using OSPF, verify that the following conditions have been met:

    Routers in the area have the same Authentication Type configured.

    All routers on the same network have the same Authentication Password configured for the interface to the network.

    All routers on the same network have the same Hello Intervals configured for the interface to the network.

    The state of each neighbor is either two-way or full in TCPCON (select Protocol Information > OSPF > Neighbors). If it is not, one of the two conditions described next will occur. Refer to the next two paragraphs for an explanation of the corrective actions required.

    In TCPCON, there is a router link state advertisement for each router in your area (select Protocol Information > OSPF > Link State Advertisements). If these advertisements are not present, verify that the missing router is active and the correct area ID is configured for the network interface.

    In TCPCON, the number of link state advertisements, Area Boundary Routers, and Autonomous System Boundary Routers are the same for each router in your area (select Protocol Information > OSPF > Areas). Verify that the problem routers are active. Bring down any router whose routing database is not synchronized with the databases of its routing neighbors. If the problem persists, reduce the size of your network or add more memory to the router.

• Routes are not exchanged on a LAN.

  Verify that the broadcast address is correct.

• RIP routes are not accessible to hosts on OSPF networks.
  • Check the status of the Autonomous System Boundary Router statistic in TCPCON (select Protocol Information > OSPF).
  • Verify that no filters are configured that would block access to the network.

IP Address Duplication across Machines

• When you are trying to bind an IP address, you get an error message stating a conflict for the IP address.
  • Set allow ip address duplicates command off under SET parameters.

Server Not Responding under Heavy Stress Conditions

Increase the following using the SET command options:

Maximum Packet Receive Buffers

Minimum Packet Receive Buffers

TCP IP Maximum Small ECBs

Load Not Balanced across NICs although LB is enabled in INETCFG

Load balancing might have been enabled only for the system and not for the particular group. Check whether you have grouped multiple NICs and enabled load balancing for them.

To check that load balancing is enabled at group level, do the following:

1. Load INETCFG and select Protocols > TCP/IP.

   In the screen that appears load balancing should enabled. This is for the complete system. You still need to verify whether load balancing is enabled for the particular Net Group.

2. Select Load Balancing Configuration > Configure Individual Group.

3. Select the particular Net Group and check whether load balancing is enabled for it. If not, set it to Yes.

Network Traffic Is Not Balanced across NICs

• If the application is binding to the local host (0.0.0.0), the data is always sent through the Primary. So the Primary should be inside the LBFT group for the load to be evenly balanced.

  Check whether the interface designated as Primary is within the group or not. If not, either group the Primary interface or make one of the group members Primary.

• If the application is not bound to the local host, then the data is always sent through the host where the application is bound. To load balance in this case, make sure that this host is inside the LBFT Group.

To check whether a particular binding is part of the LBFT Group, do the following:

1. Load INETCFG and select Bindings > TCP/IP.

2. In the screen that appears, select the Configure TCP/IP Bind option.

3. Make sure that the group interface for LBFT is set to Yes.

Losing INETCFG Configuration Information upon Rebooting

This could happen if the server abended while being configured. This corrupts the file SYS:\ETC\TCPIP.CFG. Delete this file and copy a backup of the previous configuration.

Loss of Secondary IP Address upon Deleting Any Binding

This could happen if more than one interface are using the same driver. If this is the case, never delete any of the bindings. Always disable them if you don't want to use them.