Configuring gre tunnel hangs in "gre wait"

[Dave Huang <khym%azeotrope.org@localhost>]

The gre(4) manpage gives the following instructions for creating a gre 
tunnel:

# ifconfig greN create
# ifconfig greN A D netmask 0xffffffff linkX up
# ifconfig greN tunnel A D

"ifconfig gre0 create" works fine for me, but "ifconfig gre0 10.3.1.1 
10.4.1.1 netmask 0xffffffff link0 up" hangs ifconfig in "gre wait":

UID   PID PPID CPU LID NLWP PRI NI  VSZ  RSS WCHAN    STAT TTY      TIME 
COMMAND
  0 13244   38   0   1    1  85  0 3100 1040 gre wait D    ttyp0 
0:00.01 ifconfig gre0 10.3.1.1 10.4.1.1 netmask 0xffffffff link0 up

I'm running -current as of a couple minutes ago (Feb 5 2011) on i386.