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

[Alex Balashov]

The problem mainly has to do with troubleshooting.  Sometimes you need 
to know whether a customer's CPE is genuinely down on the WAN side, and 
not necessarily the LAN interface where the head of the routed block 
typically is.  To make that work, it helps to have real transport IPs on 
the WAN interface.

There is no reason why you need to "waste" IP address on the /30s - who 
said they have to be public IPs?  Just carve out some address space out 
of a 10.0.0.0/8 range and use private transport IPs.  All you need them 
for is to test end-to-end connectivity from the aggregation router on 
your side, not for any other reachability purpose.  If they pay for 1 
static IP you can throw it up on a loopback interface on the other side 
and add a /32 route for it over the transport /30 block.

Justin Shore wrote:

> 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
> 
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-- 
Alex Balashov
Evariste Systems
Web    : http://www.evaristesys.com/
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