I have a scenario to configure VPN IP sec tunnels between Cisco 3640 router and Nortel device, can any body help on this? Is their any compatibility issues between Cisco and Nortel?
You can start here check bellow links, IPsec is prety much an industry standard so as long both routers cisco and nortel do support Ipsec you should be ok, follow the Ike Phase-1 configuration as well as phase-2 , both sides have to coninside and match whichever policy both sides agreed on.