One thing you might consider to alleviate the issue, is to stop routing at the edge and backhaul the customers at each location in a VLAN via VPLS to the PPPoE NAS/BRAS. That way you can maintain small routing tables at the edge for MPLS/OSPF and put the larger /32 table in a core router/NAS that has more memory and capacity.
Using MPLS to backhaul VLANs from the last mile is very common in large Telco/DSL networks with PPPoE so that you don't need large route tables at every site.
Thank you for your answer. You put some new conecpts to my attention and I am in the way to understand them. As you say I could bring my customers do NAS using VPLS. We are using EoIP for this and in the edge I do not need the routing table of the PPPoE customers. That's the point: how can I not have this at the edge of the network?
The layout I put here is just a small part. We have more than 900 devices in our routing space and at least 9000 routes and almost 8000 are PPPoE Sessions. Most of the orther routes could be small at some point. For example there are several /30 networks over 172.16.0.0/20 and some points in the network they should only see 172.16.0.0/20 and not every single /30. This is where my knowledge of routing is making me ask.
I will learn more about VPLS/MPLS and see how to use this inside my network. Thank you.
Is there anything to stop you placing the NAS units themselves into the PPPoE OSPF area? If you can do then Router01 becomes the ABR between Area 0 and PPPoE. You can then use Area Range on Router01 to summarize the 192.168.0.X/32 routes coming from the PPPoE area into (e.g.) a /24. At that point Router01 will still have the individual /32 entries pointing to the relevant NAT but Router02 and Router03 will only see a (e.g.) /24 route.
I don't know if what I done is the right thing. So let's me explain:
Router01 is connected to Router02 and Router03 using backbone area (0.0.0.0) and Router01-02-03 are receiving all /32. So I setup on Router01 an AreaRange for the network 192.168.0.0/24 (considering all my PPPoE Sessions are 192.168.0.0/32) over the area backbone. Router02 and Router03 are still receiving all /32.
So, for me to set Router01 as an ABR it needs to connect to Router02 and Router03 throu another area? So if my BorderRouter is distributing default routes it will still do? For this layout I will need to make some arrangements in my IP Address spaces so every area get only IPs from that area. Is this correct?