> I have the following (working) IPv4-only network situation
>
>                     x.253/29   x.254/29  192.168/16
> [The 'net] --- [Modem] --------- [NetBSD] -----------[LAN]
>                                 ne0      rtk0
>
> The NetBSD (1.6RC1-i386 if that matters) box working as a NAT for the
> network. IP forwarding is enabled.
>
> Since I have one more address available to my use (x.252) I'd like to
> have one of the boxes on the LAN (call that xxx) to have that address
> and skip NAT.
>
> What I did was:
> set up xxx to have as address x.252 and default gateway x.254
> set up NetBSD box to have rtk0 alias x.254/29
> route change x.252 -ifp rtk0 (for reachability)

you made an error generally looking - defined different and not bridged
network with same network address and netmask

try adding on NetBSD:

arp -s x.252 ne0_MAC_address pub

so your ISP (or your modem if it's doing routing) will know on it's
ethernet (ne0 in your netbsd) that 252 should be put to your netbsd BOX.

the real solution is:

do this arp -s .....



leave your internal network 192.....

define extra IP number on target machine as an alias /32

add route -host <this IP> 192.168.a.b

on NetBSD box