Duplicate IP address are observed for Virtual Machines when HA mode of the Gateway is changed

Products

• VMware NSX

Issue/Introduction

• NSX segments are configured to use Gateway DHCP server to get IP address configuration for Virtual Machines.
• Issue is observed when Tier-1 gateway HA mode is changed from Active-Standby to Distributed only.
• This problem can also be observed when T1 gateway's Edge cluster is changed.

Environment

VMware NSX

Cause

This issue occurs because the DHCP leases is not synchronized between the Active Edge node of the old Edge Cluster and the Active Edge node of the new Edge Cluster.

Consequently, the Active Edge node in the new cluster, unaware of the leases issued by its predecessor, may reassign an IP address that is currently in use by a different VM (allocated by the old Active Edge).

The DHCP Server instance is always instantiated on the T1 Gateway's currently configured Edge Cluster, even if a different Edge Cluster is specified within the DHCP Server profile.

Resolution

This is an expected behavior as DHCP leases are not synchronized between the NSX Edges [Active Edge from old Cluster to Active Edge from new Cluster] where the Gateway DHCP Server is instantiated.