PPPoE and firewall

RouterOS General
1

I have a following configuration:

ISP-----ADSL modem (bridged)-----(eth5-pppoe)RB450G-----LAN

I am configuring firewall, modification of NetworkPro on firewalling http://wiki.mikrotik.com/wiki/NetworkPro_on_firewalling

I am not using physical interface - eth5 in any firewall rule, instead I am using virtual PPPoE interface (for example, NAT masquared rule, illegal addresses on WAN interface, allowed services on WAN interface, etc.).
So, I am interested could there be any rule in firewall, in this type of configuration, where I need to use physical interface eth5 instead of virutal PPPoE interface?
Such case doesn’t come to my mind, because all WAN traffic goes through PPPoE interface anyhow, but maybe I am missing something…

2

for example
You can explicitly specify the mac address in the rule ppoe server

3

I am not sure I understand the answer?

I don’t have PPPoE server, I am connecting customer to ISP with PPPoE client.