tap interface detached

[Frédéric Fauberteau <frederic%fauberteau.org@localhost>]

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?