Cisco config:

vpdn-group VPDN-CORP-L2TP
accept-dialin
    protocol l2tp
    virtual-template 2
lcp renegotiation on-mismatch
l2tp security crypto-profile L2TP
no l2tp tunnel authentication
ip pmtu
ip mtu adjust

crypto isakmp policy 100
hash md5
authentication pre-share

crypto isakmp key presharedkey address 0.0.0.0 0.0.0.0

crypto ipsec transform-set L2TP esp-3des esp-md5-hmac
mode transport

crypto map L2TP 100 ipsec-isakmp profile L2TP
set transform-set L2TP

interface FastEthernet0/0.901
encapsulation dot1Q 901
ip address 10.1.1.1 255.255.255.0
ip flow ingress
ip nat inside
ip virtual-reassembly
crypto map L2TP

interface FastEthernet0/0.900
encapsulation dot1Q 900
ip address 10.0.0.254 255.255.255.0
ip flow ingress
ip nat inside
ip virtual-reassembly
crypto map L2TP

interface Virtual-Template2
ip address 10.0.100.2 255.255.255.0
ip nat inside
ip virtual-reassembly
autodetect encapsulation ppp
no peer default ip address
ppp authentication ms-chap-v2 

#sh ver
Cisco IOS Software, C2600 Software (C2600-ADVENTERPRISEK9-M), Version 12.4(10a), RELEASE SOFTWARE (fc2)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2006 by Cisco Systems, Inc.
Compiled Wed 11-Oct-06 18:15 by prod_rel_team

ROM: System Bootstrap, Version 12.2(8r) [cmong 8r], RELEASE SOFTWARE (fc1)

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Cisco 2651XM (MPC860P) processor (revision 3.1) with 253952K/8192K bytes of memory.
Processor board ID FOC08310PYP
M860 processor: part number 5, mask 2
2 FastEthernet interfaces
2 Serial(sync/async) interfaces
1 terminal line
1 Virtual Private Network (VPN) Module
1 cisco ids sensor(s), ids monitoring on slot 1
32K bytes of NVRAM.
32768K bytes of processor board System flash (Read/Write)

Configuration register is 0x2102