This started as a question, with my connection failing to come up, but after a bit of trial and error, the configuration is working, so I've edited it into a solution. Access lists and address translation is not 100% in the config below yet, but it covers the connection setup.
The setup: I have a Cisco router with 2 ethernet ports and another ADSL router with the ATM interface. My service provider offers a static IP for ADSL via an L2TP tunnel (l2tp service ip, shared secret provided, adsl username / password for auth). I want to configure the connection and the tunnel on the Cisco - 1 ethernet port internal (fa0/1), with the L2TP tunnel interface being the external / public IP on the other ethernet port (fa0/0) - but also still maintain a private network between the Cisco and other DSL router.
Internal network: 192.168.0.0/24 Private network between Cisco and other router: 10.0.0.0/24 (or could be /30). Other router is configured in PPPoE bridge mode / pass through. L2TP service: 1.2.3.4 Shared secret: 54321 ADSL username / pass: myuser@myisp / mypass
aaa new-model
aaa authentication ppp default local
l2tp-class l2tp_secret
hidden
authentication
hello 10
password 54321
pseudowire-class l2tp_config
encapsulation l2tpv2
protocol l2tpv2 l2tp_secret
ip local interface Dialer1
interface FastEthernet0/0
description WAN / PPPoE Interface
ip address 10.0.0.10 255.255.255.0
ip virtual-reassembly
pppoe enable group global
pppoe-client dial-pool-number 10
interface FastEthernet0/1
description LAN
ip address 192.168.0.1 255.255.255.0
ip nat inside
ip virtual-reassembly
ip tcp adjust-mss 1412
no ip mroute-cache
interface Virtual-PPP1
description L2TP Tunnel for static IP
ip address negotiated
ip mtu 1452
ip nat outside
ip virtual-reassembly
ip tcp adjust-mss 1412
shutdown
no cdp enable
ppp authentication pap callin
ppp pap sent-username myuser@myisp password 0 mypass
pseudowire 1.2.3.4 1 pw-class l2tp_config
interface Dialer1
ip address negotiated
encapsulation ppp
shutdown
dialer pool 10
ppp authentication pap callin
ppp pap sent-username myuser@myisp password 0 mypass
ppp ipcp route default
ip route 0.0.0.0 0.0.0.0 Virtual-PPP1
ip route 1.2.3.4 255.255.255.255 Dialer1