Ping the loopback interface on your server

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

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

i5/OS™ 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, i5/OS reserves the IP address ::1 and the line description *LOOPBACK for this purpose. The IPv6 loopback interface does not have a corresponding host name because the local host tables do not currently support IPv6 addresses. However, you can use a Domain Name System (DNS) to store the IPv6 host name instead of using the local host table.

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

At the command line, type these commands:
- For IPv4: PING '127.0.0.1' or PING LOOPBACK
- For IPv6: PING '::1'
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.

Failures might indicate the following problems.

Problem	Recovery
The local host table does not have an entry for the IPv4 LOOPBACK host name and IP address of 127.0.0.1.	You need to add the entry to the host table. This is only relevant for IPv4 because host tables do not currently support IPv6. To verify the host table entries, follow these steps: At the command line, type `CFGTCP` (Configure TCP/IP). Select option 10 (Work with TCP/IP Host Table Entries). Verify that the host table contains an entry for the LOOPBACK host name and IP address 127.0.0.1.
The loopback interface is not active.	To activate the loopback interface: At the command line, type `NETSTAT`. Select option 1 (Work with TCP/IP interface status) for IPv4 interfaces, or select option 4 (Work with IPv6 interface status) for IPv6 interfaces. 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.

Problem

Recovery

The local host table does not have an entry for the IPv4 LOOPBACK host name and IP address of 127.0.0.1.

You need to add the entry to the host table. This is only relevant for IPv4 because host tables do not currently support IPv6. To verify the host table entries, follow these steps:

At the command line, type CFGTCP (Configure TCP/IP).
Select option 10 (Work with TCP/IP Host Table Entries).
Verify that the host table contains an entry for the LOOPBACK host name and IP address 127.0.0.1.

The loopback interface is not active.

To activate the loopback interface:

At the command line, type NETSTAT.
Select option 1 (Work with TCP/IP interface status) for IPv4 interfaces, or select option 4 (Work with IPv6 interface status) for IPv6 interfaces.
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.