Distributed Transit Gateway (DTGW) External VLAN gateway resolution failure Alarm

Products

• VMware NSX

Issue/Introduction

Title: Alarm for Distributed Transit Gateway (DTGW) External VLAN gateway resolution failure
Event ID: tgw_distributed_vlan_connection.dtgw_vlan_uplink_arp_fail

Alarm Description:

• Purpose: Notify about ARP resolution for the DTGW External VLAN gateway failure. Alarm is raised if the rate of ARP resolution failure is higher than the threshold and it will be cleared when the ARP resolution is successful. The default threshold for the rate is calculated based on the ARP resolution state machine in ESX. If there is one flow, ESX will try to resolve the ARP for the Gateway by sending one ARP request per second 3 times. If ARP resolution fails in all 3 attempts then the ARP entry is marked as unresolved and the failure rate is 0.33 per second. The Alarm is raised at a Transport node level which means it incorporates the state of all external VLAN connections on the Host. So, if there are multiple connections with some of them failing to resolve the gateway, then the Alarm could be raised.
• Impact: North-South traffic for the VMs in the VPC with DTGW will not work if the gateway is not resolved.

Environment

• VMware NSX
• VCF 9.0

Cause

Gateway resolution can fail due to the following reasons:

• DTGW gateway attachment VLAN configuration is incorrect
• DTGW gateway attachment Gateway IP/CIDR configuration is incorrect
• Gateway is not reachable from the ESX host

Resolution

Steps to Resolve
For VCF 9.0 and higher

Recommended Actions:

• Check if the DTGW attachment configuration is incorrect and use the UI/API to update it.
• Check if the underlay networking is set up correctly and the ESX host is able to reach the Gateway.
• Use Traceflow Tool in NSX to trace the packet's path when pinging the external gateway from the VM.

Additional Information

• NSX Admin Guide: https://docs.vmware.com/en/VMware-NSX/index.html
• NSX API Guide: https://developer.broadcom.com/xapis/nsx-t-data-center-rest-api/latest/