Hello Mahmoud,
As to your question, do you mean by "real IP" a static public IP for the outside interfaces of the routers?
Normally, in a L2L enviroment, you enter the public IPs in the configuration in order to negotiate a VPN tunnel between the 2 peers.
However, you can configure it so that 1 side uses a static public IP (leased line) while the other side uses a changing IP (DHCP assigned for example).
For the first senario, use the router configuration in the link below
http://www.cisco.com/en/US/products/ps9422/products_configuration_example09186a0080b4ae61.shtml
For the second Scenario, Use the below suggestions
For Site A, use the router configuration in the link below.
http://www.cisco.com/en/US/products/ps9422/products_configuration_example09186a0080b4ae61.shtml
The following commands need to be added instead of the ones in the link:
crypto ipsec transform-set myset esp-3des esp-sha-hmac
crypto ipsec security-association lifetime seconds 28800
crypto ipsec security-association lifetime kilobytes 4608000
crypto dynamic-map mydyn 10 set transform-set myset
crypto map mymap 65535 ipsec-isakmp dynamic mydyn
crypto map mymap interface outside
and
crypto isakmp key hostname
= Fully qualified domain name.
For Site B, use the same configuration as in the link but make the following changes:
crypto isakmp peer address
set aggressive-mode password
set aggressive-mode client-endpoint fqdn
