re-configure the adsl router from running router-mode to bridge-mode, then configure pppoe on the pix if isp authentication is required.
with this scenario, the public ip will be assigned directly on the pix outside interface, and the router will act as a dump adsl signal "handler". thus, you don't have to worry about the complication of nat, firewall rule etc.
it's not feasible to configure pppoe on the pix with the posted scenario.
the reason being with the pppoe configured on the pix, the router will have no ip address at all and runs as a bridge. the only function of the router is then to translate the dsl signal. without a layer 3 device in front of the dmz, host will not be able to connect to the internet.
i suggest a purchase of cisco router, such as 837/877, replacing the existing adsl router.
www <--> 837/877 <--dmz--> pix <--> inside
837/877 router is capable to handle adsl, firewalling, and vpn. thus the segment between the roter and the pix can be used as a dmz; whereas the pix can be used to secure the inside subnet.
further, the primary advantage of 877 over 837 is the wireless capability.
nonetheless, below are the codes for configuring pppoe on pix:
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...