Network Connectivity Loss to Default Gateway After VM Deployment via AWX or Template

Products

• VMware vSphere ESXi

Issue/Introduction

• The default gateway connection fails after VM deployment via AWX job or from a VM template.
• The virtual machine is unable to reach anything outside of the subnet.
• The network adapter is connected and visible in the guest OS, but no traffic flows.
• Workaround: vMotioning the VM to a different host or toggling the network adapter (disconnect/reconnect) restores connectivity.

Environment

VMware vSphere ESXi 6.x, 7.x, 8.x

VMware vCenter Server 6.x, 7.x, 8.x

Cause

 

• Packet captures recorded at the ESXi host uplink layer show outbound ICMP echo requests leaving the virtual switch architecture successfully, while corresponding inbound replies fail to return from the physical network infrastructure.

• Since the Layer 2 access layer switches maintain a stable, non-flapping Content Addressable Memory (CAM) entry for the virtual machines' MAC addresses on the physical switch ports, local switching layers operate properly.

• Because the Layer 2 domain fabric is verified stable and traffic drops occur outside the virtual boundary, the breakdown is isolated further upstream at the Layer 3 network routing boundary or an asymmetric routing path.

• The issue occurs when the upstream Layer 3 default gateway (Core Router) maintains a stalled, out-of-sync, or corrupted ARP cache table for newly deployed or dynamic virtual machine network profiles.

 

Resolution

 

• Engage the Physical Network Infrastructure Team to inspect and manage the upstream Layer 3 core routing boundaries.

• Flush and clear the stale or stalled ARP cache table entries corresponding to the provisioned virtual machines' IP and MAC address configurations directly on the Layer 3 default gateway device (Core Router).

• Audit the core network architecture pathing for upstream asymmetric routing dependencies or multi-homed paths that block inbound responses from routing back to the verified ESXi host uplinks.

• For cluster environments experiencing high-frequency automated deployments (e.g., via automated AWX provisioning tasks), configure a lower ARP cache timeout threshold on the Layer 3 Core Router to match dynamic virtual machine lifecycle operations.

 

 

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