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Why is there a large Destination Unreachable count in the NETSTAT STATS report?

Question & Answer


Question

Output from a NETSTAT STATS command shows a large number in the following fields, and they increase every time the report is run:

  ...
 ICMP Statistics                             
                             Received    Sent
                             --------    ----
  ...
   Destination Unreachable   nnnnnn      nnnnnn
 ...
 UDP Statistics
  ...
   No Port Errors        = nnnnnn

While there are some differences between these numbers, they are increasing at roughly the same rate.

Answer

The TCPIP stack and OMPROUTE have their SNMP SubAgents enabled by default. If the SNMP Agent (typically OSNMPD) is not running on this system, both of these SubAgents will constantly retry the initial contact to the agent's port (UDP 161). The resultant packets will create an instance of each of the above counts. If a packet trace is collected on the system, it will show regular UDP messages being sent to port 161 with the source and destination IP address being the same.

If there is a need to support SNMP queries for this stack, configure and start the OSNMPD task. If there is no plan to support SNMP queries, disable the SubAgent in both the TCPIP PROFILE (SACONFIG DISABLE) and the OMPROUTE configuration (ROUTESA_CONFIG ENABLED=NO).

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Product Synonym

ZOSCS COMMSERVER

Document Information

Modified date:
13 June 2018

UID

dwa1453292