VM fails to get IPv6 address via DHCPv6 Relay in a dual stack topology

Products

• VMware NSX

Issue/Introduction

• VMs are not receiving IPv6 from DHCP server. 
• VMs constantly sending DHCP solicitation message to DHCP server. 
• When DHCPv6 is responding with  "noAddr" for VMs 

Environment

VMware NSX

Cause

The DHCPv6 server contains a binding entry associated with the VM’s ethY MAC address. However, the client DUID (stored in /var/lib/dhcp/dhclient6.leases) was generated using the ethX MAC address instead of ethY.

During the DHCPv6 exchange, the server extracts the client’s MAC address from the DUID to identify the corresponding binding.
Since the DUID references ethX, while the server expects ethY, the MAC address does not match.
As a result, the DHCPv6 server cannot associate the request with an existing binding and responds with NoAddr (no address assigned).

Resolution

• Remove the /var/lib/dhcp/dhclient6.lease from VM and then run dhclient again on ethX like "dhclient -6 -d -v eth1
  • rm /var/lib/dhcp/dhclient6.lease 
  • dhclient -6 -d -v ethY

Workaround:

• Use dhcpv6 server pool instead of binding for the dhcpv6 server