Cisco Secure Virtual Private Networks








10.6
IKE
Mode Configuration



10.6.1
Mode
configuration overview: address assignment challenge





This
section covers IKE mode configuration. Mode configuration is
designed to address the issues that arise when VPN clients are
assigned dynamic IP addresses.
In client-initiated access VPNs, the
remote users' VPN clients start Point-to-Point Protocol (PPP) links
with local ISP's network access servers (NASs). After VPN clients
have been assigned dynamic IP addresses by their Internet service
provider (ISP), it is difficult for the corporate gateway to
administer scalable IPSec policy for all those VPN clients. The figure
to the left shows that a new IPSec policy is required for each VPN client
because each has a dynamic IP address that is assigned by different
ISPs and that is outside of the corporate subnet's IP address range.