SNAT port usage high alarm triggered even though active sessions are not high

Products

• VMware NSX
• VMware NSX-T Data Center

Issue/Introduction

• Critical alarm "SNAT Port Usage On Gateway Is High" is seen continuously for SNAT IP, even though there are not many active connections
• You see messages similar to the following in the syslog:
  
  2023-04-14T18:05:10.037Z nsxmgr-03 NSX 5281 MONITORING [nsx@6876 alarmId="927cab4a-####-####-####-36f3a55a14b5" alarmState="OPEN" comp="nsx-manager" entId="62a03bb6-####-####-####-a7279c6a0ca6" errorCode="MP701099" eventFeatureName="nat" eventSev="CRITICAL" eventState="On" eventType="snat_port_usage_on_gateway_is_high" level="FATAL" nodeId="62a03bb6-####-####-####-a7279c6a0ca6" subcomp="monitoring"] SNAT ports usage on logical router 42ecb79b-####-####-####-c3e599c41862 for SNAT IP 10.10.10.10 has reached the high threshold value of 80%. New flows will not be SNATed when usage reaches the maximum limit.
• The review the actual usage, use the following commands on the node UUID reported in the alarm, for example above it is: nodeId="62a03bb6-####-####-####-a7279c6a0ca6"
  • Log in as the admin user on Edge node and invoke the NSX CLI command `get firewall <LR_INT_UUID> connection state`. 
  • LR_INT_UUID is the interface to which the SNAT rule is applied.
    • Note: If the SNAT rule is not applied to any specific interface, use any Uplink interface UUID for the logical router.
  • Check the UDP/TCP flows listed out

"NAT Active/Max": "9/4294967295",
"NAT Active/Max": "3/4294967295",
"NAT Active/Max": "0/4294967295",
"NAT Active/Max": "6/4294967295",

Note: The first number before the '/' is the used counter, and the number on the right is the available count.

Environment

VMware NSX-T Data Center
VMware NSX

Resolution

This issue is resolved in VMware NSX 3.2.4
This issue is resolved in VMware NSX 4.1.1, 4.2.0

 

Workaround:

Disable the alarm under "Alarm Definitions". This should avoid the alarm from re-appearing.

Make sure to re-enable the alarm after you complete the upgrade successfully.