Pinging the loopback interface on your system

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To verify that your TCP/IP software is installed, started, and working properly, ping the loopback interface.

You can perform the test without being connected to a physical line or network.

IBM i reserves the IP address 127.0.0.1, the host name LOOPBACK, and the line description value of *LOOPBACK for verifying the software. Similarly for IPv6, IBM i reserves the IP address ::1, the host name IPV6-LOOPBACK, and the line description *LOOPBACK for this purpose.

To ping the loopback interface on your system to troubleshoot the problem, follow these steps:

  1. At the command line, type these commands:
    • For IPv4: PING '127.0.0.1' or PING LOOPBACK
    • For IPv6: PING '::1' or PING 'IPV6-LOOPBACK'
    See PING parameters to fine-tune the PING command to get the most accurate results. Prompt on the PING command by selecting F4 for complete details on the PING parameters.
  2. Identify the problem and apply the corresponding recovery method.
    Problem Recovery
    The local host table does not have an entry for one of the following pairs of host name and IP address:
    • IPv4: LOOPBACK, 127.0.0.1
    • IPv6: IPV6-LOOPBACK, ::1

    You need to add the entry to the host table. To verify the host table entries, follow these steps:

    1. At the command line, type CFGTCP (Configure TCP/IP).
    2. Select option 10 (Work with TCP/IP Host Table Entries).
    3. Verify that the host table contains an entry for one of the following pairs of host names and addresses:
      • IPv4: LOOPBACK, 127.0.0.1
      • IPv6: IPV6-LOOPBACK, ::1
    The loopback interface is not active.

    To activate the loopback interface:

    1. At the command line, type NETSTAT.
    2. Select option 1 (Work with TCP/IP interface status) for IPv4 interfaces, or select option 4 (Work with IPv6 interface status) for IPv6 interfaces.
    3. Scroll down to find the loopback interface (127.0.0.1 or ::1), and select option 9 (Start) from the Work with TCP/IP interface status menu.
    TCP/IP has not been started. To start TCP/IP, type STRTCP (Start TCP/IP) at the command line.