Jim Besse wrote:

> My customer currently has a private LAN with ip addresses in the
> range of 199.199.199.xxx accessing a UNIX server.  All the
> workstations are WIN9X PCs.  They now need an Internet connection
> and I recommended a Linksys BEFSR41 to connect to a DSL line.  Do I
> have to change all the existing addresses to the 192.168.1.xxx  or
> 192.168.0.xxx range or can I keep the existing addresses?  They
> have no idea why the 199 addresses were used rather than the 10. or
> 192. private address.

  If you install the router without doing NAT, these users will not
be able to connect to anything on the Internet because any server
that they try to connect to will send its responses to machines
belonging to the registered owners of the 199.199.199.xxx address
space (Shane Young, a network engineer with Minnesota Regional
network).  Not good.

  If you install the router *with* NAT, they should be able to
connect to almost everybody else on the Internet -- EXCEPT any hosts
in the 199.199.199.xxx block, since their machines think these are
local addresses and will not send them out through the router.

  Both problems are avoided by using NAT with one of the ranges
reserved for this purpose by RFC 1918: 10.xxx.xxx.xxx, 172.16.xxx.xxx
- 172.31.xxx.xxx, and 192.168.xxx.xxx.

  [It is fairly obvious that the person who set up their network
wanted this effect, but didn't know about RFC 1918 -- their network
*may* date back to before its existence.]

Dave Gillett

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