Thank you for your response.
It seems to only be an issue for VMs requesting DHCP from my Comcast connection. I’ve seen this issue with both VyOS and the Sophos XG virtual appliance. It has also been an issue on both Proxmox and VMware ESXi. Any VM on the host that requests a DHCP address from my standalone router receives it right away.
The cable modem is an Arris SB8200. It connects to an access port on my Juniper EX2200 switch. From there, I trunk the VLAN over an aggregated Ethernet bundle to my Proxmox host. The Linux bond is part of a VLAN aware Linux bridge to which the VyOS VM is attached. On that VM, I have a VyOS VIF that is associated with my WAN VLAN.
If I check the MAC address table on the Juniper switch I can see both the MAC address of the modem and the MAC address of the VM. When I run a packet capture from with VyOS, I see the DHCPDISCOVER leaving the host. I’ve also seen the DHCPDISCOVER packets coming out of the server when running a packet capture attached to the server NIC. I need to re-run the packet capture from a switch mirror port to see whether or not the modem is returning any offers (I am not seeing them when running the capture on the VyOS VM). As soon as I connect the modem to a VyOS instance running on bare metal, VyOS gets an address straight away.