Netstat knows about "-f inet6".

usr.bin/netstat/netstat.1

@@ -1,4 +1,4 @@
-.\"	$NetBSD: netstat.1,v 1.23 1999/09/12 02:33:43 dbj Exp $
+.\"	$NetBSD: netstat.1,v 1.24 1999/09/15 19:57:02 is Exp $
 .\"
 .\" Copyright (c) 1983, 1990, 1992, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -112,6 +112,9 @@ are recognized:
 .Ar inet ,
 for
 .Dv AF_INET ;
+.Ar inet6 ,
+for
+.Dv AF_INET6 ;
 .Ar ns ,
 for
 .Dv AF_NS ;