IP addresses question

> As IP address space is becoming quite scarce these days, we don't want to 
> use registered addresses for the ISDN network (it doesn't have to be 
> visible from the Internet).
> 
> We have three solutions :
> - use RFC1597 addresses, but there is no reverse DNS for such addresses 
> (problem when doing a traceroute)
> - use some kind of unnumbered scheme, but it's difficult to manage on 
> Cisco routers with multiple dial-in BRI.
> - use a registered addresses anyway ...
> 
> Any advice, experience ?

 We use dynamic unnumbered links with a router from Securicor 3net (are you 
 stuck with Cisco?) and it works *very* well.

 Cheers

John