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

[Gregory Boehnlein]

>> We send our default route out of the interface, rather than to the remote
gateway IP, so if we change the
>> ip of the loopback on our side, we do not need to adjust anything for the
>> customer.
> 
> That's not a bad idea.  Though wouldn't pointing a default at an
> interface force it to ARP constantly?  Several hundred CEs ARPing
> non-stop could be a load issue on your PE.

I've not experienced that.
 
> I'm not too worried about the loopback's IP changing.  I only put a /24
> on the loopback to get us started.  I'll load it with customer DS1s
> until I get to around 90% IP utilization and then create another
> loopback with another /24 or perhaps a /23 this time around.  I padded
> the front of the subnet sufficiently to allow for future HA projects
> and the unforeseeable.  I can't foresee ever needing to change the IP on a
> loopback once I have it in production.

It makes it much easier to groom services from one router to the other if
you have to migrate a lot, and over the years, I have had to migrate a lot
of customers from one router to the next etc..

> > We use outbound service policies on unnumbered interfaces just fine:
> >
> > interface Serial10/1/0/3:0
> >  description L3 OH/XXXX/XXXX to XXXXXXX channel 12
> >  ip unnumbered Loopback0
> >  no ip redirects
> >  no ip unreachables
> >  no ip proxy-arp
> >  service-policy output llq
> >  no fair-queue
> >  down-when-looped
> >  no clns route-cache
> 
> Excellent.  QoS was something that occurred to me as I was writing my
> original message.
> 
> 
> > ip route X.X.X.X 255.255.255.248 Serial10/1/0/3:0 name CustomerRouteA
> 
> So you'd prefer to route a larger customer assignment to the the
> CE-facing interface instead of to their assigned IP unnumbered address?
> 
> > I've been doing ip unnumbered since 1995 in production and it "just
> works".
> > There are undoubtedly some routers out there that might have issues,
> but any
> > Cisco device should be able to handle things just fine.
> 
> Very good.  On the CE side I really don't anticipate many problems.  I
> see this as more of a CE knowledge thing than anything.  I'm sure we'll
> have several customers that need something special.  I hope that for
> the most part we can lump them all into an IP unnumbered design.

To be truthful, I haven't found anything that we cannot do w/ IP unnumbered
yet.