I think I'm missing something here... I feel like this should "just 
work" because I've been doing this for years... Keep your eyes on the 
bouncing broadcast....

mail# ifconfig fxp1 down ; ifconfig fxp1 delete ; ifconfig fxp1 inet 
66.11.84.97 netmask 0xffffff0
mail# ifconfig fxp1
fxp1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
         address: 00:90:0b:04:5e:f4
         media: Ethernet autoselect (100baseTX full-duplex)
         status: active
         inet 66.11.84.97 netmask 0xffffff0 broadcast 242.11.84.111
         inet6 fe80::290:bff:fe04:5ef4%fxp1 prefixlen 64 scopeid 0x2

mail# ifconfig fxp1 down ; ifconfig fxp1 delete ; ifconfig fxp1 inet 
66.11.84.97 netmask 255.255.255.240
mail# ifconfig fxp1
fxp1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
         address: 00:90:0b:04:5e:f4
         media: Ethernet autoselect (100baseTX full-duplex)
         status: active
         inet 66.11.84.97 netmask 0xfffffff0 broadcast 66.11.84.111
         inet6 fe80::290:bff:fe04:5ef4%fxp1 prefixlen 64 scopeid 0x2

mail# ifconfig fxp1 down ; ifconfig fxp1 delete
mail# ifconfig fxp1 inet 66.11.84.97 netmask 0xfffffff0
mail# ifconfig fxp1
fxp1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
         address: 00:90:0b:04:5e:f4
         media: Ethernet autoselect (100baseTX full-duplex)
         status: active
         inet 66.11.84.97 netmask 0xfffffff0 broadcast 66.11.84.111
         inet6 fe80::290:bff:fe04:5ef4%fxp1 prefixlen 64 scopeid 0x2


Now, the reason I noticed this is because when the machine boots, with 
/etc/ifconfig.fxp1 set to:

mail# cat /etc/ifconfig.fxp1
inet 66.11.84.97 netmask 0xffffff0

...the broadcast is wrong... I always do netmasks in hex because I 
can't do math in base10.

NetBSD mail 2.0_RC5 NetBSD 2.0_RC5 (GENERIC) #1: Sun Nov 14 04:18:00 
CST 2004  gendalia@satai:/usr/obj/i386/GENERIC i386