Router:
WAN Interface, IP:	123.123.123.13 (Single public IP)
LAN interface, IP:	192.168.5.1 (all incoming traffic is routed to 192.168.5.2)

ASA 5505:
WAN Interface, IP:	192.168.5.2 /30
LAN Interface, IP:	192.168.11.250 / 24

--------------------------------------------------------------------

:
ASA Version 7.2(3) 
!
interface Vlan1
 nameif inside
 security-level 100
 ip address 192.168.11.250 255.255.255.0 
!
interface Vlan2
 nameif outside
 security-level 0
 ip address 192.168.5.2 255.255.255.252 
!
interface Ethernet0/0
 switchport access vlan 2
!
interface Ethernet0/1
!
interface Ethernet0/2
!
interface Ethernet0/3
!
interface Ethernet0/4
!
interface Ethernet0/5
!
interface Ethernet0/6
!
interface Ethernet0/7
!
ftp mode passive
clock timezone CET 1
clock summer-time CEDT recurring last Sun Mar 2:00 last Sun Oct 3:00
dns server-group DefaultDNS
 domain-name dg.local
same-security-traffic permit intra-interface

access-list acl_out extended permit tcp any host 192.168.5.2 eq www
access-list acl_out extended permit tcp any host 192.168.5.2 eq ftp
access-list acl_out extended permit tcp any host 192.168.5.2 eq smtp
access-list acl_out extended permit tcp any host 192.168.5.2 eq pop3
access-list acl_out extended permit tcp any host 192.168.5.2 eq 5500
access-list acl_out extended permit udp any host 192.168.5.2 eq 5505
access-list acl_in extended permit ip any any

icmp unreachable rate-limit 1 burst-size 1
asdm image disk0:/asdm-523.bin

global (outside) 1 interface
nat (inside) 1 0.0.0.0 0.0.0.0
static (inside,outside) tcp 192.168.5.2 www 192.168.11.200 www netmask 255.255.255.255 
static (inside,outside) tcp 192.168.5.2 ftp 192.168.11.200 ftp netmask 255.255.255.255 
static (inside,outside) tcp 192.168.5.2 5500 192.168.11.20 5500 netmask 255.255.255.255 
static (inside,outside) udp 192.168.5.2 5505 192.168.11.20 5505 netmask 255.255.255.255 
static (inside,outside) tcp 192.168.5.2 smtp 192.168.11.21 smtp netmask 255.255.255.255 
static (inside,outside) tcp 192.168.5.2 pop3 192.168.11.21 pop3 netmask 255.255.255.255 

access-group acl_out in interface outside
access-group acl_in in interface inside

route outside 0.0.0.0 0.0.0.0 192.168.5.1 1

http server enable
http 192.168.11.0 255.255.255.0 inside

no snmp-server location
no snmp-server contact

snmp-server enable traps snmp authentication linkup linkdown coldstart
class-map inspection_default
 match default-inspection-traffic
!
!
policy-map type inspect dns preset_dns_map
 parameters
  message-length maximum 512
policy-map global_policy
 class inspection_default
  inspect dns preset_dns_map 
  inspect ftp 
  inspect h323 h225 
  inspect h323 ras 
  inspect rsh 
  inspect rtsp 
  inspect esmtp 
  inspect sqlnet 
  inspect skinny 
  inspect sunrpc 
  inspect xdmcp 
  inspect sip 
  inspect netbios 
  inspect tftp 
  inspect http 
  inspect ils 
  inspect pptp 
!
service-policy global_policy global
ntp server 213.251.160.83 source outside

group-policy default-domain internal
group-policy default-domain attributes
 vpn-idle-timeout 30
tunnel-group default-domain type ipsec-ra
tunnel-group default-domain general-attributes
 default-group-policy default-domain
: end