As of this publication, the Cisco Secure VPN Client is supported with Cisco networking devices using Entrust, Microsoft, and VeriSign digital certificates. An IPSec software image loaded onto the networking device from a supported Cisco IOS software release. Choosing a VPN network design that best fits the needs of your business is essential. Some client maintenance is required. No client maintenance is required.
Network is more scalable with digital certificates than with pre-shared keys.
You can configure unlimited clients. Network is less scalable with pre-shared keys than with digital certificates. Router must be reconfigured with each additional client. One workaround is to use wildcard pre-shared key. Scalable to larger networks.