Hiding private addresses Was Re: Port Scan

[rod at tpgi.com.au]

<snip>
> > Hop 20: I didn't think that 192.168.17.1 was a routable address, or have
> > I misunderstood something?  Or is this a case of IP spoofing in the act?

David Gibson wrote: 
> 
> More likely an ISP that's using the private address for a hop inside
> their network and haven't configured their routers properly to hide it
> from the outside world.

Is the requirement to hide all private addresses completely or just to 
ensure that you never exchange/advertise external routing info about 
them? 

We use them internally on hops that have no need for a visible IP (ie 
intra router links). Traceroutes from outside do show the IP just as in 
the above example but we dont advertise them outside that LAN (just 
a couple of static routes).  

Do we need to somehow block traceroute etc replys from these 
machines as well? If so any suggestions on how?

Cheers
-RodT