(RADIATOR) Dynamic IP assignment criteria

[Claudio Lapidus]

Hello all,

Sorry if this is a bit off-topic, this is not a configuration question, but 
a more 'best practices' one...

We have an ADSL access network (12 BRAS nodes, about 100K subscribers and 
growing...) that we use to provide wholesale Internet access to a number of 
ISPs. Currently we manage the whole IP numbering space ourselves, and assign 
dynamically from static IP pools locally configured in each BRAS. This is 
complemented by static routes in the backbone edge to advertise the local 
pools of each BRAS.

So the IP space is subdivided according to the physical topology of the 
access network, with each BRAS handling a contiguous portion of the IP 
space. This means that subscribers from each particular ISP (across 
different BRASs) do not receive contiguous IP numbers, and a certain IP can 
be assigned to different ISP's subscribers at different times. This in turn 
difficults troubleshootings, abuse tracking, etc.

Now we have been required to partition our IP space and delegate each 
portion to the corresponding ISP, so they can know in advance the IP range 
that is allocated to its users. That is, we are going to implement an 
administrative partitioning of the IP space, which is 'orthogonal' from the 
physical topology criteria we are using so far.

The dilemma here is wether to go with individual IP assignment (via 
Framed-IP-address), or an intermediate scheme of assigning pools 'on demand' 
to each BRAS (according to IP usage for each particular ISP), and how to 
properly advertise this assignments to routing, always avoiding the 
propagation of countless /32 routes into the backbone.

I would love to hear abour any experience you guys might have regarding this 
point, especially about pool size vs. impact on routing updates frequency, 
centralized (in Radius server) vs. distributed management (in BRAS 
perhaps?).

thanks in advance
cl.

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