Eu finalmente consegui que funcione, aqui estão as seções da minha configuração que fizeram:
interface ATM0
no ip address
shutdown
no atm ilmi-keepalive
pvc 0/38
encapsulation aal5mux ppp dialer
interface FastEthernet0
!
interface FastEthernet1
!
interface FastEthernet2
switchport access vlan 101
!
interface FastEthernet3
!
interface Vlan1
description $ETH-SW-LAUNCH$$INTF-INFO-HWIC 4ESW$$FW_INSIDE$
ip address 10.193.125.254 255.255.255.0
ip nat inside
ip virtual-reassembly
zone-member security in-zone
!
interface Vlan101
no ip address
no ip redirects
no ip unreachables
no ip proxy-arp
ip virtual-reassembly
pppoe enable group global
pppoe-client dial-pool-number 1
!
interface Dialer1
description $FW_OUTSIDE$
mtu 1492
ip address negotiated
no ip unreachables
ip nat outside
ip virtual-reassembly
zone-member security out-zone
encapsulation ppp
dialer pool 1
dialer-group 1
no cdp enable
ppp chap hostname
ppp chap password 0
ppp ipcp route default
!
ip forward-protocol nd
ip http server
ip http authentication local
ip http secure-server
ip http timeout-policy idle 60 life 86400 requests 10000
!
ip nat inside source list 1 interface Dialer1 overload
!
ip access-list extended NAT
permit ip 10.193.125.0 0.0.0.255 any