The command "ip protocol" on a sub interface

Hi, I have started a new job at an ISP of my country and right now they're having me doing the deletion of customers that are no longer with us. I am trying to understand this kind of configuration that I see on a lot of the interfaces I have to delete

interface ATM2/0.911 point-to-point description "xxxxxxxxxxxxxxxxx" ip unnumbered Loopback9 no atm enable-ilmi-trap pvc 201/130 protocol ip 89.97.3.143 ubr 1024 oam-pvc manage encapsulation aal5snap interface Loopback9 description "Interface Internet Top" ip address 89.97.3.129 255.255.255.128 ip authentication mode eigrp 12874 md5 ip authentication mode eigrp 11 md5 ip authentication key-chain eigrp 12874 FWPoP ip authentication key-chain eigrp 11 FWPoP ip ospf network point-to-point end 

So as far I understand the /25 network is given to an access device like a DSLAM/MSAN or something, there's a lot of the interfaces on the PoP that have the "ip unnumbered" command I assume it is done like that to make it easy to add/delete customers without having to type each time an ip address and just

The ip protocol command I am not too sure what it does, the ip after it is the IP of the CPE at the customer's site so, is it just a declaration of what the next hop is or is it a way to sorta create a "fake" point to point link?

Thanks for the help