[c-nsp] DS1 provisioning using IP Unnumbered vs /30s

[Justin Shore]

I'm curious to see what everyone's take is on handling the addressing of 
customer-facing DS1s.  Rather than provision a /30 per customer and 
waste IP space I'm planning on using IP unnumbered to a loopback for the 
vast majority of our most basic DS1 customers.  They'll get assigned 1 
IP out of the pool and if they request (and pay for) any more then I'll 
static route their allocation to their pool IP.  We'll also request that 
they only use the statically-routed subnet for server assignments and 
not PAT their pool IP; that way they can be migrated to our LRE solution 
  with minimal IP and DNS changes as LRE becomes available in their 
local CO.

I'm prepared to offer /30s where needed of course, in case their CPE 
runs into trouble for some reason or in case they wig out over the 
thought of their external interface being in the same bcast domain as 
other customers.  I'm actually looking at options to restrict bcasts 
between IP unnumbered serial interfaces too.  We need to allow direct
access between the sites but not bcast.

One of my concerns is QoS.  We'll be offering QoS-enabled VoIP over 
these DS1s in some cases.  Can I still use service-policies on physical 
interfaces or would it have to be on the loopback and apply to all 
users?  I have not tried QoS and IP unnumbered yet.  Perhaps VoIP 
circuits will have to be addressed with /30s (or /31s since we're 
managing the CE in VoIP installations).

I know that IP unnumbered works in general; I'm just wondering if anyone 
has already done it in production and ran into problems?  My goal is to 
not waste IP space on network and bcast addresses where possible.  No, 
I'm not going to assign /31s; customers just won't be able to comprehend 
that, especially when the IOS through our a warning message when you 
assign a /31 to an interface.  I use /31s internally but not for 
customer links.  IP unnumbered wastes the least amount of IP space. 
Since we're targeting our services at the low-end of the SMB market who 
most likely it already on CATV or RBE DSL and share a bcast domain with 
their neighbors already, I don't envision IP unnumbered to be a big 
deal.  I'm looking for guidance though.  Thoughts?

Thanks
  Justin