paravirtualized adapter doesn't receive packets until a ping6 of the gateway

[jasonmader]

OpenBSD 6.7 guest on macOS Catalina, where the guest is configured for IPv6-only and a paravirtualized network bridged adapter. After booting the OpenBSD guest, and obtaining the IPv6 address by autoconfiguration, the Internet seems unreachable. Simultaneous packet captures on the guest and the host show, for example, a DNS request egress the guest and the host, and the DNS response ingress the macOS host but not the OpenBSD guest. A workaround is to ping6 the IPv6 gateway public address, then suddenly packets for the guest will start showing up in the guest packet capture.

However, the ping6 also inserts the neighbor entry for the IPv6 gateway public address. Otherwise, because of autoconfiguration, the Internet6 default route is the IPv6 gateway link-local address and there is only the gateway's link-local address in the neighbor mapping table.

[jasonmader]

While the network isn't working, the gateway router is sending,

Source           Destination     Protocol  Length  Info
fe80::gate:wayy  2601::open:bsd  ICMPv6    86      Neighbor Solicitation for 2601::open:bsd from b4:00:ga:te:wa:yy

which I can observe on the macOS host, but tcpdump on the guest doesn't show this packet. The guest obtained it's IPv6 public address by SLAAC, so the VirtualBox bridged adapter should have seen the address. That seems to be why it takes a ping6 2601::gate:wayy (which is sent from the IPv6 public address, not the link-local address) to start receiving packets with the guest's IPv6 public address.

[jasonmader]

I've tried the other interface models, and they show the same problem of not forwarding the gateway router's Neighbor Solicitation to the guest.