bin/51881: tcpdump fails on bridge interface

[amonk%backwatcher.com@localhost]

>Number:         51881
>Category:       bin
>Synopsis:       tcpdump fails on bridge interface
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Jan 15 11:20:00 +0000 2017
>Originator:     Kyle Amon
>Release:        7.0.2
>Organization:
BackWatcher, Inc.
>Environment:
NetBSD nbsd.backwatcher.com 7.0.2 NetBSD 7.0.2 (XEN3_DOM0.201610210724Z) amd64
>Description:
The tcpdump tool fails to function on a bridge interface, at least
under Xen with a NetBSD 7.0.2 dom0.

As you can see, the bridge exists...

root@nbsd ~ # ifconfig bridge0
bridge0: flags=41<UP,RUNNING> mtu 1500

As you can see the bridge has members...

root@nbsd ~ # brconfig -a
bridge0: flags=41<UP,RUNNING>
        Configuration:
                priority 32768 hellotime 2 fwddelay 15 maxage 20
                ipfilter disabled flags 0x0
        Interfaces:
                tap2 flags=3<LEARNING,DISCOVER>
                        port 8 priority 128
                xvif1i0 flags=3<LEARNING,DISCOVER>
                        port 9 priority 128
                wm0 flags=3<LEARNING,DISCOVER>
                        port 1 priority 128
        Address cache (max cache: 100, timeout: 1200):
                04:73:35:f1:d5:7d wm0 982 flags=0<>
                04:8d:0a:ac:38:2e wm0 979 flags=0<>
                aa:00:00:d1:00:09 xvif1i0 972 flags=0<>
                00:22:83:0e:07:c0 wm0 941 flags=0<>
                04:34:a5:e2:f6:6a wm0 682 flags=0<>
                04:ad:49:7d:a4:9a wm0 563 flags=0<>
                04:d6:62:ba:01:c1 wm0 215 flags=0<>
                04:83:9a:11:4d:c8 wm0 -163 flags=0<>

Everything with respect bridging itself is working, but tcpdump
does not work with the bridge interface, as you can see...

root@nbsd ~ # tcpdump -n -i bridge0 icmp
tcpdump: bridge0: No such device exists
(BIOCSETIF failed: Device not configured)
>How-To-Repeat:
Try to use tcpdump on a bridge interface in dom0.
>Fix:
Unknown.