IPv6 Problem with Bhyve

[Hiroshi Nishida]

I'm sorry but I sent my first e-mail in an HTML format.

Hi,
I already asked the same question at 
https://forums.freebsd.org/threads/ipv6-tcp-connection-issue-with-bhyve.76771/ 
but haven't got any responses yet.
I'd like to ask also here to figure out what causes this problem.

I could install Windows Server 2019 on FreeBSD 12.1R + bhyve by mostly 
following https://wiki.freebsd.org/bhyve/Windows but have the following 
problem swith TCP/IPv6:

* All firewalls are turned off on both host FreeBSD and guest Windows.
* The guest Windows is assigned to a static IPv6 address and a DHCP'ed 
IPv4 address.
* Accessing the guest Windows using IPv4 is all OK including RDP, 
telnet, etc and vice versa.
* I can ping from the guest Windows to all IPv6 addresses, vice versa.
* However, accessing the guest Windows and accessing from the guest 
Windows through TCP/IPv6 all fail.

Please take a look at 
https://forums.freebsd.org/threads/ipv6-tcp-connection-issue-with-bhyve.76771 
for a tcpdump log on a tcp connection trial from host FreeBSD to guest 
Windows.
Briefly speaking, the 3-way connection does not establish because the 
host FreeBSD ignores (?) the SYN-ACK from the guest Windows.

As for the guest Windows -> the host FreeBSD, the guest sends a SYN 
packet to the host but the host FreeBSD does not respond to it.
The connection trial packet from the guest -> Internet goes through 
tap0, bridge0 and igb0 but does not seem to reach our IPv6 gateway.

Interestingly, I have exactly the same problem also with CentOS 8 + 
KVM/QEMU.

I would appreciate it if anybody could tell me how to fix this.
Thank you.

-- 
Hiroshi Nishida
ASUSA Corporation