The agent-addr field of snmp warmStart and coldStart trap is not set correctly when vCenter has multiple NICs

Products

• VMware vCenter Server

Issue/Introduction

• Monitoring software may fail to detect vCenter warmStart and coldStart snmp traps under the following conditions:
  • vCenter has multiple NICs
  • SNMP target is configured to connect from 2nd or later NIC
  • Monitoring software filters snmp traps by agent-addr field
• The 'snmp.test' API of the vCenter Appliance Shell is also affected as it sends warmStart.
• The snmp trap sent by the vCenter alarms are NOT affected.

Environment

VMware vCenter Server 7.0.x

Cause

The packet is actually received by the snmp target, but is filtered because the agent-addr does not match the source IP.

Example of a Packet Sent

Internet Protocol Version 4, Src: <IP address of ethX>, Dst: <SNMP target>   ##<-- Source IP is that of ethX.
User Datagram Protocol, Src Port: 37677, Dst Port: 162
Simple Network Management Protocol
 ::
        trap
            enterprise: 1.3.6.1.6.3.1.1.5 (iso.3.6.1.6.3.1.1.5)
            agent-addr: <IP address of eth0>                                 ##<-- agent-addr is that of eth0
            generic-trap: warmStart (1)
 

In the current vCenter implementation, the IP address of the NIC connected to the default gateway is selected as the agent-addr for warmStart and coldStart trap.

Resolution

Currently, there is no resolution.