The bottom line is how to configure the VPNs and the flexiblity of the configuration. The router is a router, first and foremost. While it can be configure to pass VPNS, site to site VPNs it does not have the flexiblity nor the processing power of the concentrator.
The concentrator on the other hand is very flexible in configuring the VPN endpoint or passthrough. Groups, permissions, routes, interfaces, RADIUS are all relatively easy to configure unlike the router. It has both a GUI HTTP front end and a CLI for the GUI-adverse. You can offer DHCP served addresses to the clients or static, you can push client updates out and configure an VPN "cluster". Something near and dear to the admin's heart is the ablity to use NT authentication with a few clicks of a mouse.
Even as strong as the 7200 series is, the number of VPNs you are talking about could easily overpower the CPU unless you have some type of onboard/card for VPN acceleration. The router is having to route traffic AND handle the encryption/decryption of the packets which is process intensive depending on the key size and prototocol. THe router also can not be configured nearly as well for redundency (ie..clustering). You can have HSRP or VRRP but there are some issues with VPNs depending on configuration.
We tried with dual 7200s running HSRP and ended up with a pair of concentrators talking to the NT boxes and to a RADIUS box. This was for 300 or so remote connections (sales, stores etc) We were going to put in a second concentrator for the store to store connections when I left that project.
We have not even touched on the raw performance issues surrounding a full T3 worth of VPN traffic.. thats ALOT of encryption/decryption for any device to do so something like a cluster very well may be in your future.
Get the entire book on the 3000 series configuration here:
MikeS
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