how do I disable IPv6?

[steve%prd.co.uk@localhost (Steve Blinkhorn)]

The following message repeats endlessly and frequently on the console
and in /var/log/messages:

Feb 27 16:12:08 rockall ntpd[11099]: bind(29) AF_INET6
fe80::2c2:c6ff:fe48:7b0a%2#123 flags 0x11 failed: Can't assign
requested address
Feb 27 16:12:08 rockall ntpd[11099]: unable to create socket on iwn0
(10) for fe80::2c2:c6ff:fe48:7b0a%2#123
Feb 27 16:12:08 rockall ntpd[11099]: failed to init interface for
address fe80::2c2:c6ff:fe48:7b0a%2

From /var/run/dmesg.boot:

iwn0: DAD detected duplicate IPv6 address fe80:2::2c2:c6ff:fe48:7b0a:
NS in/out=
1/1, NA in=0
iwn0: DAD complete for fe80:2::2c2:c6ff:fe48:7b0a - duplicate found
iwn0: manual intervention required
iwn0: possible hardware address duplication detected, disable IPv6

I make no (conscious) use of IPv6, and all IPv6 services
are commented out in inetd.conf.  /etc/ifconfig.iwn0 contains just an
IPv4 address; wpa_supplicant.conf contains just ssid and password
pairs.   But ifconfig -a includes in its result:

iwn0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        ssid PRD nwkey
65536:"",0x2a08a4ed58cb286906667be4402c8279,0xf9c529c7c79f487f7e93577751604e78,""
        powersave off
        bssid 28:28:5d:92:ca:5c chan 3
        address: 00:c2:c6:48:7b:0a
        media: IEEE802.11 autoselect (DS1 mode 11g)
        status: active
        inet 193.117.57.198 netmask 0xfffffe00 broadcast 193.117.57.255
        inet6 fe80::2c2:c6ff:fe48:7b0a%iwn0 prefixlen 64 duplicated scopeid 0x2

What I can't find is where and how to disable IPv6 - perhaps do
something with /etc/rc.d/network?

The configuration files I have worked under 6.x and I haven't had
cause to concern myself with iwn0 since I moved to 7.0, at least not
until now.

I imagine the answer will be shorter than the question...

-- 
Steve Blinkhorn <steve%prd.co.uk@localhost>