Netmaster Smarttrace - Display shows INVALID CHECKSUM error

Products

• CMDB for z/OS
• NetSpy Network Performance
• NetMaster Network Automation
• SOLVE
• NetMaster Network Management for SNA
• NetMaster Network Management for TCP/IP
• NetMaster File Transfer Management

Issue/Introduction

When reviewing a Smarttrace, one of these messages is appearing:

*WARNING* Invalid Header Checksum.

or

*WARNING* Invalid Header Checksum. Checksum offload feature may be in use.

or

*NOTE* Found invalid checksum. Checksum offload feature maybe in use.

 

 

Environment

Release:
Component: NMTIP

Resolution

If Smarttrace is showing

*WARNING* Invalid Header Checksum.

this indicates an actual problem on an inbound packet and you will need to investigate the cause.

Reviewing this same data in IPCS would most likely show the same error message.

If Smarttrace is showing

*WARNING* Invalid Header Checksum. Checksum offload feature may be in use.

or

*NOTE* Found invalid checksum. Checksum offload feature maybe in use.

These are for outbound packets and are informational. The messages will most likely NOT appear when the same data is viewed in IPCS.

Smarttrace may also show the checksum itself with a value of '0000'.

 

 

Additional Information

When a link device uses a checksum offload function, outbound packets will contain invalid checksum values as the stack expects the link device to calculate the correct checksum value before sending the packet to the network.

When viewing the file in IPCS, IPCS is reading/analyzing the CTRACE DSN. It knows this interface is using the OFFLOAD feature and knows not to validate the checksum.

Smarttrace reads the results from the IPCS formatted display and highlights the discrepancy as NetMaster doesn't know whether offload is in use or not so therefore writes an informational message indicating what was found.