There are no advantages or disadvantages other than what should be obvious.
Advantage: Simple administration, common config on all routers.
Disadvantage: Potentially allows anyone to connect to the router from the Internet if not forbidden by another policy on the router.
Advantage: ISAKMP can not be negotiated if not specifically configured on the router for that remote IP address. Conceptually more secure.
Disadvantage: More administrative overhead.
With 3 sites, the specific key per site is fairly easy to do. If you had 200 sites, that method would be much less doable. You could do a quick estimate. (N * 5) + (N ^ 2) minutes to do your entire network, or something in that line.
It's much easier if you have a system that manages this for larger installs. I believe this is the one of the purposes of Cisco's GET VPN.
BenefitsDocumentationPrerequisiteImage Download LinksLimitationsSupported PlatformsLicense RequirementsTopologyStep-By-Step ConfigurationConfigure Virtual ServiceActivate the virtual service and configure guest IPsConfiguring UTD (Service Plane)Configurin...
Login to the FXOS chassis manager.
Direct your browser to https://hostname/, and log-in using the user-name and password.
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We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...