What is this IPoE/Proxy ARP like feature called?

[luke_r_godwin]

This is a novelty question rather than a "I need to know this in order to fix something" question.

I have an Australian NBN 'IPoE' service and use a linux router.
My VDSL modem is bridged and merely forwards L2 frames to the linux host. The linux host sends regular DHCP messages.
It gets a response with a DHCP lease with a subnet mask of 255.255.224.0 (/19).

Below is a redacted via of the linux-host's ARP table:

user@linux-host$ arp -e -n -i wan
Address HWtype HWaddress Flags Mask Iface
203.59.96.X ether 70:0f:6a:mm:mm:mm C wan
203.59.97.Y ether 70:0f:6a:mm:mm:mm C wan
203.59.97.Z ether 70:0f:6a:mm:mm:mm C wan
203.59.96.255 ether 70:0f:6a:mm:mm:mm C wan

The "255" entry is the default gateway, some Cisco BNG router, presumably.
The "X", "Y" and "Z" entries are what interest me.
Those are not addresses of any device I control and appear to be other subscribers.
Yet I see they have the same MAC address as the ISP default gateway. The IP addresses respond to ICMP and other traffic.

What is the name of the feature that tells this cisco device to perform some version of what looks like Proxy ARP?

[Deepak Kumar]

Hi,

If I got properly then it is also called proxy-arp and on Cisco router and switches it is enabled by default. As I am understanding your question and seems like Proxy-ARP is disabled on the router where you are checking this entry. 

[luke_r_godwin]

the cisco device is not something i have access to; it is owned by the ISP. my question is an attempt to learn by inference rather than direct examination.