With GNS 0.7 you can try the following.
Two routers connected back to back with a Static Virtual Tunnel Interface.
You can try we AH only, Static keys, Dynamic keys, and various ESP NULL, ESP DES
Two routers back to back with crypto map and the above options
Two routers back to back and one acting as the certificate server
You can use PIX 8.0 with single and multiple context. PIX to PIX or PIX to Router
You can use the ASA simulator
You can use DMVPN with a Hub and Spoke over Frame Relay and PPPoE
Many of these are within CLN discussions but if you would like to try them you could publish them on CLN for others to try.
i will definitely send what i will try for beginners like me either brief document or a lab once in every 7 days.
also 2 routers back to back u means connected together by fastethernet or serial interfaces.
i tried to configure Site to Site VPN using SDM but it only shows interface fastethernet not serial.& what if i connects 2 routers together through fastethernet interface will i be able to implement VPN technologies....
Below is an example of using the AUX port on two router. It has a speed of 38K. It uses ESP-NULL so no encryption just authentication. It uses static keys. There is a GRE tunnel over the crypto link so it can carry multicast traffic.
This is an example of the many forms a VPN can take.
Paul ran a weekly Security Discussion a few months ago it might be worth reading those discussions.
ip address 192.168.1.2 255.255.255.0
async default routing
async mode dedicated
crypto map CM
crypto ipsec transform-set T1 esp-null esp-sha-hmac
crypto map CM 10 ipsec-manual
set peer 192.168.1.3
set session-key inbound esp 300 authenticator 9988776655443322110099887766554433221100
set session-key outbound esp 300 authenticator 9988776655443322110099887766554433221100
set transform-set T1
match address 100
ip address 10.0.0.5 255.255.255.252
tunnel source 192.168.1.2
tunnel destination 192.168.1.3
access-list 100 permit ip any any