Problem with KVM/QEMU Guest + IPv6

[ScopeDog]

I'm running Windows 10 on KVM/QEMU assigned to a static IPv6 address and a DHCP'ed IPv4 address. All firewalls are turned off on both CentOS and Windows. I can ping6 to/from the guest Windows from/to everywhere. However, no other IPv6 services such as HTTP, SSH, RDP, are accessible from/to the guest Windows 10. IPv4 is working well and I can ssh/rdp from/to the guest Windows. I guess there is a problem with my bridge or IPv6 settings but does anybody know how to fix this?

The following are the bridge and vnet devices (and I have noticed that br0 dropped some packets..):

Code: Select all

br0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.0.111  netmask 255.255.255.0  broadcast 192.168.0.255
        inet6 fe80::d6a2:25e4:256:711  prefixlen 64  scopeid 0x20<link>
        inet6 2001:XXX:YYY:0:827c:9c9a:5877:58c3  prefixlen 64  scopeid 0x0<global>
        inet6 2001:XXX:YYY::1000:1  prefixlen 64  scopeid 0x0<global>
        RX packets 17361  bytes 5887577 (5.6 MiB)
        RX errors 0  dropped 691  overruns 0  frame 0
        TX packets 1774  bytes 312240 (304.9 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        
vnet0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet6 fe80::fc54:ff:feea:ea1b  prefixlen 64  scopeid 0x20<link>
        ether fe:54:00:ea:ea:1b  txqueuelen 1000  (Ethernet)
        RX packets 15308  bytes 9268039 (8.8 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 46180  bytes 42050353 (40.1 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

I can also show an IPv6 sysctl output if needed but net.ipv6.conf.br0.forwarding = 1 didn't work.

Thank you so much.

[ScopeDog]

Here is additional information.
I'm currently checking packets with tcpdump and have the following weird results:

1. RDP to Windows guest is reset by TCP RST from the Windows guest. This means the original packet reached the Windows guest at least.
2. SSH from Windows guest to CentOS host sends TCP SYN packets to CentOS but CentOS never responds.

Well, I'm not very familiar with both Windows and CentOS and don't know what causes this...