System information
Troubleshooting ATM Switching Environments 21-443
Using the ping Command
Looping Trunk Ports
This procedure outlines the steps for looping data through a trunk, the physical and logical
connections between two LightStream 2020 trunk ports. If you know that data is not passing on a
trunk between two trunk ports, follow these steps to set up a remote loop on one of the trunk ports:
Step 1 Enter the set port port-number loop remote command. The port is set to testing mode
and the loopback test begins automatically.
Step 2 If the remote loop succeeds, the trunk port comes up at the remote end. If the local port
displays an operational status of down during the loopback test, there is probably a
problem with the local port. Proceed to Step 3.
If the remote loop fails and the trunk does not come up, then a problem exists somewhere
between the local access card and the remote system.
Step 3 To run an internal loop on the port, enter the set port port-number loop internal
command. The port is set to testing mode and the loopback test begins automatically.
Step 4 If the internal loop succeeds and the local trunk comes up, the problem is the local access
card.
Step 5 To stop the loopback test, enter the set port port-number unloop command.
Looping Edge Ports
This procedure outlines the steps for looping data through an edge port. The line from the port
connects a LightStream 2020 ATM switch to a third-party external device. If you suspect that data
is not passing between the LightStream 2020 edge port and the host, or that the line is unreliable, use
this looping procedure to isolate the problem:
Step 1 If the port is a Frame Relay User-Network Interface (UNI) port, enter the set port
port-number framerelay netinterfacetype nni command to set the netinterfacetype
attribute to Network-to-Network Interface (NNI).
Internal loopback tests do not work on Frame Relay ports with the Local Management
Interface (LMI) type set to UNI.
Step 2 Run a remote loop on the LightStream 2020 edge port by entering the set port
port-number loop remote command. The port is set to testing mode and the loopback test
begins automatically.
Step 3 If the internal loop fails and the line does not come up, the problem is in the line or access
card.
Step 4 To stop the loopback test, enter the set port port-number unloop command.
Step 5 If you changed a Frame Relay UNI port to NNI for the loopback test, reset the port to the
UNI network interface type by entering the set port port-number framerelay
netinterfacetype uni command.
Using the ping Command
The ping command is useful for determining whether communication is possible over a particular
Internet Protocol (IP) connection. The ping command sends an Internet Control Message Protocol
(ICMP) echo packet to the speciļ¬ed IP address. If communication with that address is possible, the
host replies with an ICMP-echo-reply message.