When both l2pop and arp_responder enabled for linuxbridge agent, vxlan device is created in "proxy" mode. In this mode, ARP entry must be statically added by linuxbridge agent. Because of [1], l2pop driver won't notify HA router port, so linuxbridge agent can't add ARP entry for router port. As there is no router ARP entry, vxlan device is dropping ARP request packets from vm(destined to router), making vm unable to communicate with router.
This issue is only on linuxbridge agent and not on ovs agent.
Temporary solution for vm to communicate with HA router is to disable arp_responder when l2pop is enabled.
If the users need both arp_responder and l2pop features for linuxbridge agent, we need an implementation which decouples them i.e https://bugs.launchpad.net/neutron/+bug/1518392
[1] https://review.openstack.org/#/c/255237/
This is intentional. We don't use l2pop to teach agents about internal networks connected to HA routers. The agent is supposed to learn these addresses via normal switching / MAC learning.
Are you seeing any connectivity issues?