Configure A Vpn - Cisco CISCO851-K9 - 851 Integrated Services Router Configuration Manual

Configure a VPN

GRE Tunnels
GRE tunnels are typically used to establish a VPN between the Cisco router and a remote device that
controls access to a private network, such as a corporate network. Traffic forwarded through the GRE
tunnel is encapsulated and routed out onto the physical interface of the router. When a GRE interface is
used, the Cisco router and the router that controls access to the corporate network can support dynamic
IP routing protocols to exchange routing updates over the tunnel, and to enable IP multicast traffic.
Supported IP routing protocols include Enhanced Interior Gateway Routing Protocol (EIGRP), Routing
Information Protocol (RIP), Intermediate System-to-Intermediate System (IS-IS), Open Shortest Path
First (OSPF), and Border Gateway Protocol (BGP).
Note When IP Security (IPSec) is used with GRE, the access list for encrypting traffic does not list the desired
end network and applications, but instead refers to the permitted source and destination of the GRE
tunnel in the outbound direction. All packets forwarded to the GRE tunnel are encrypted if no further
access control lists (ACLs) are applied to the tunnel interface.
VPNs
VPN configuration information must be configured on both endpoints; for example, on your Cisco router
and at the remote user, or on your Cisco router and on another router. You must specify parameters, such
as internal IP addresses, internal subnet masks, DHCP server addresses, and Network Address
Translation (NAT).
Configuration Tasks
Perform the following tasks to configure this network scenario:
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A configuration example showing the results of these configuration tasks is provided in the
"Configuration Example" section on page
The procedures in this chapter assume that you have already configured basic router features as well as
Note
PPPoE or PPPoA with NAT, DCHP, and VLANs. If you have not performed these configurations tasks,
see
Chapter 4, "Configuring PPP over ATM with NAT,"
and VLANs,"
Configure a VPN
Perform the following tasks to configure a VPN over an IPSec tunnel:
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Cisco 850 Series and Cisco 870 Series Access Routers Software Configuration Guide
7-2
Configure a VPN
Configure a GRE Tunnel
Chapter 1, "Basic Router Configuration," Chapter 3, "Configuring PPP over Ethernet with NAT,"
as appropriate for your router.
Configure the IKE Policy
Configure Group Policy Information
Enable Policy Lookup
Configure IPSec Transforms and Protocols
Configure the IPSec Crypto Method and Parameters
Apply the Crypto Map to the Physical Interface
Chapter 7 Configuring VPNs Using an IPSec Tunnel and Generic Routing Encapsulation
7-9.
and Chapter 5, "Configuring a LAN with DHCP
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