tap interface detached

Hi,

I am trying to install a Xen domU and I am reproducing a working 
configuration for NetBSD 9.0 amd64 from a running host.

I create a tunnel interface:

     # ifconfig tap0 create
     # ifconfig tap0 inet 192.168.0.1 up

I add this interface to a bridge:

     # ifconfig bridge0 create
     # brconfig bridge0 add tap0 up

The tap interface appears to be detached:

     # ifconfig tap0
     tap0: flags=0x8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> 
mtu 1500
             ec_capabilities=0x5<VLAN_MTU,JUMBO_MTU>
             ec_enabled=0x1<VLAN_MTU>
             description: "Xen VM tunnel"
             address: f2:0b:a4:fb:22:75
             status: no carrier
             inet6 fe80::f00b:a4ff:fefb:2275%tap0/64 flags 0x8<DETACHED> 
scopeid 0x4
             inet6 2001:bc8:3807:101::1/64 flags 0x8<DETACHED>
             inet 192.168.0.1/24 broadcast 192.168.0.255 flags 0x4<DETACHED>

Nevertheless, the DHCP client that is executed by the NetBSD installer 
in the domU succesfully gets an IP address (192.168.0.2). But ping the 
dom0 fails:

     # ping -c 4 192.168.0.1
     PING 192.168.0.1 (192.168.0.1): 56 data bytes
     ping: sendto: Host is down
     ping: sendto: Host is down

     ----192.168.0.1 PING Statistics----
     4 packets transmitted, 0 packets received, 100.0% packet loss

I don't remember doing any specific thing to "attach" the tap0 interface 
on NetBSD 9.0. Dis I miss something?