Hi,
Found http://www.nbnco.com.au/content/dam/nbnco2/documents/sfaa-wba2-product- catalogue-nebs-product-tech-spec-fttb-fttn_20150824-to-FTTN-launch.pdf, which suggests each DSL port will accept up to 8 mac addresses, and expire unseen mac's after 300 seconds. May be simply a modem limit then. Time for more playing!
But if you only have one interface attached to that broadcast domain, then pppoe client interface should be the only MAC that is presented to the modem.
BTW, keep meaning to ask.. How far up the expense (and physical footprint) ladder do I need to go, to get a MT device which will do 100mbps of PPTP traffic? (CRS109 tops out at 100% cpu at around the 45mbps mark..) Had been considering doing a RouterOS VM at home and DC with routing preferencing pushing traffic over PPTP/EOIP tunnel between them if they're up, and falling back to the CRS109's at each end if either VM is down, but if there is a MT router which doesn't take much space which will handle it, and doesn't cost the earth, it might just be easier to go that way :)
Don't know about that - pppoe should not consume so much CPU just to run the ppp interface - perhaps there is something else going on there. Try running profiler tool when CPU is pegged to try to find out what subsystem is using up CPU. Cheers! Mike.