I haven’t used a pppoe setup yet, but I searched in vain for a way to use circuit-id to select dhcp pools on the MikroTik and gave up. It appears that the MikroTik does not support option 82. I was using a Cisco SOHO router that supported dhcp-class (circuit-id) before replacing it with the MikroTik. My solution was to allow each router I was using to manage it’s own dhcp pool until I get a radius or central dhcp server.