Allowing remote users to access corporate resources using IPSec on Cisco routers can be implemented with a feature called Easy VPN. Cisco Easy VPN Server The Cisco Easy VPN Server service allows a growing number of Cisco IOS routers, PIX Firewalls, and Cisco VPN 3000 Concentrators to act as VPN head-end devices in site-to-site or remote access VPNs. These head-end devices provide the VPN connections, as well as a configuration source for the Cisco Easy VPN Remote sites.
After the Cisco Easy VPN server has been configured, a VPN connection can be created with minimal configuration on an Easy VPN remote, such as a Cisco uBR905 or Cisco uBR925 cable access router, a Cisco 800 series router, or a Cisco 1700 series router.
Table Of Contents
Configuring a VPN Using Easy VPN and an IPSec Tunnel
The Cisco 870 series routers support the creation of Virtual Private Networks (VPNs).
Cisco routers and other broadband devices provide high-performance connections to the Internet, but many applications also require the security of VPN connections which perform a high level of authentication and which encrypt the data between two particular endpoints.
Two types of VPNs are supported—site-to-site and remote access. Site-to-site VPNs are used to connect branch offices to corporate offices, for example. Remote access VPNs are used by remote clients to log in to a corporate network.
The example in this chapter illustrates the configuration of a remote access VPN that uses the Cisco Easy VPN and an IPSec tunnel to configure and secure the connection between the remote client and the corporate network. Figure 6-1 shows a typical deployment scenario.
Note The material in this chapter does not apply to Cisco 850 series routers. Cisco 850 series routers do not support Cisco Easy VPN.
Figure 6-1 Remote Access VPN Using IPSec Tunnel
Remote, networked users | |
2 | VPN client—Cisco 870 series access router |
Router—Providing the corporate office network access | |
4 | VPN server—Easy VPN server; for example, a Cisco VPN 3000 concentrator with outside interface address 210.110.101.1 |
Corporate office with a network address of 10.1.1.1 | |
6 | IPSec tunnel |
Cisco Easy VPN
The Cisco Easy VPN client feature eliminates much of the tedious configuration work by implementing the Cisco Unity Client protocol. This protocol allows most VPN parameters, such as internal IP addresses, internal subnet masks, DHCP server addresses, WINS server addresses, and split-tunneling flags, to be defined at a VPN server, such as a Cisco VPN 3000 series concentrator that is acting as an IPSec server.
An Easy VPN server-enabled device can terminate VPN tunnels initiated by mobile and remote workers who are running Cisco Easy VPN Remote software on PCs. Easy VPN server-enabled devices allow remote routers to act as Easy VPN Remote nodes.
The Cisco Easy VPN client feature can be configured in one of two modes—client mode or network extension mode. Client mode is the default configuration and allows only devices at the client site to access resources at the central site. Resources at the client site are unavailable to the central site. Network extension mode allows users at the central site (where the VPN 3000 series concentrator is located) to access network resources on the client site.
After the IPSec server has been configured, a VPN connection can be created with minimal configuration on an IPSec client, such as a supported Cisco 870 series access router. When the IPSec client initiates the VPN tunnel connection, the IPSec server pushes the IPSec policies to the IPSec client and creates the corresponding VPN tunnel connection.
Note The Cisco Easy VPN client feature supports configuration of only one destination peer. If your application requires creation of multiple VPN tunnels, you must manually configure the IPSec VPN and Network Address Translation/Peer Address Translation (NAT/PAT) parameters on both the client and the server.
Configuration Tasks
Perform the following tasks to configure your router for this network scenario:
•Configure the IKE Policy
•Configure Group Policy Information
•Apply Mode Configuration to the Crypto Map
•Enable Policy Lookup
•Configure IPSec Transforms and Protocols
•Configure the IPSec Crypto Method and Parameters
•Apply the Crypto Map to the Physical Interface
•Create an Easy VPN Remote Configuration
An example showing the results of these configuration tasks is provided in the 'Configuration Example' section.
Note The procedures in this chapter assume that you have already configured basic router features as well as PPPoE or PPPoA with NAT, DCHP and VLANs. If you have not performed these configurations tasks, see Chapter 1 'Basic Router Configuration,'Chapter 3 'Configuring PPP over Ethernet with NAT,'Chapter 4 'Configuring PPP over ATM with NAT,' and Chapter 5 'Configuring a LAN with DHCP and VLANs' as appropriate for your router.
Note The examples shown in this chapter refer only to the endpoint configuration on the Cisco 870 series router. Any VPN connection requires both endpoints be configured properly to function. See the software configuration documentation as needed to configure VPN for other router models.
Configure the IKE Policy
Perform these steps to configure the Internet Key Exchange (IKE) policy, beginning in global configuration mode:
Purpose | ||
|---|---|---|
Step 1 | crypto isakmp policypriority Example: | Creates an IKE policy that is used during IKE negotiation. The priority is a number from 1 to 10000, with 1 being the highest. Also enters the Internet Security Association Key and Management Protocol (ISAKMP) policy configuration mode. |
Step 2 | encryption {des | 3des | aes | aes 192 | aes 256} Example: | Specifies the encryption algorithm used in the IKE policy. The example specifies 168-bit data encryption standard (DES). |
Step 3 | hash {md5 | sha} Example: | Specifies the hash algorithm used in the IKE policy. The example specifies the Message Digest 5 (MD5) algorithm. The default is Secure Hash standard (SHA-1). |
Step 4 | authentication {rsa-sig | rsa-encr | pre-share} Example: | Specifies the authentication method used in the IKE policy. The example specifies a pre-shared key. |
Step 5 | group {1 | 2 | 5} Example: | Specifies the Diffie-Hellman group to be used in an IKE policy. |
Step 6 | lifetime seconds Example: | Specifies the lifetime, 60-86400 seconds, for an IKE security association (SA). |
Step 7 | exit Example: | Exits IKE policy configuration mode, and enters global configuration mode. |
Configure Group Policy Information
Perform these steps to configure the group policy, beginning in global configuration mode:
Purpose | ||
|---|---|---|
Step 1 | crypto isakmp client configuration group {group-name | default} Example: | Creates an IKE policy group containing attributes to be downloaded to the remote client. Also enters the Internet Security Association Key and Management Protocol (ISAKMP) group policy configuration mode. |
Step 2 | key name Example: | Specifies the IKE pre-shared key for the group policy. |
Step 3 | dns primary-server Example: | Specifies the primary Domain Name System (DNS) server for the group. Note You may also want to specify Windows Internet Naming Service (WINS) servers for the group by using the wins command. |
Step 4 | domain name Example: | Specifies group domain membership. |
Step 5 | exit Example: | Exits IKE group policy configuration mode, and enters global configuration mode. |
Step 6 | ip local pool {default | poolname} [low-ip-address [high-ip-address]] Example: | Specifies a local address pool for the group. For details about this command and additional parameters that can be set, see the . |
Apply Mode Configuration to the Crypto Map
Perform these steps to apply mode configuration to the crypto map, beginning in global configuration mode:
Purpose | ||
|---|---|---|
Step 1 | crypto map map-name isakmp authorization list list-name Example: | Applies mode configuration to the crypto map and enables key lookup (IKE queries) for the group policy from an authentication, authorization, and accounting (AAA) server. |
Step 2 | crypto map tag client configuration address [initiate | respond] Example: | Configures the router to reply to mode configuration requests from remote clients. |
Enable Policy Lookup
Perform these steps to enable policy lookup through AAA, beginning in global configuration mode:
Purpose | ||
|---|---|---|
Step 1 | aaa new-model Example: | Enables the AAA access control model. |
Step 2 | aaa authentication login {default |list-name}method1[method2...] Example: | Specifies AAA authentication of selected users at login, and specifies the method used. This example uses a local authentication database. You could also use a RADIUS server for this. For details, see the and . |
Step 3 | aaa authorization {network | exec | commands level| reverse-access | configuration} {default |list-name} [method1[method2...]] Example: | Specifies AAA authorization of all network-related service requests, including PPP, and specifies the method of authorization. This example uses a local authorization database. You could also use a RADIUS server for this. For details, see the and . |
Step 4 | usernamename {nopassword | passwordpassword | password encryption-typeencrypted-password} Example: | Establishes a username-based authentication system. This example implements a username of Cisco with an encrypted password of Cisco. |
Configure IPSec Transforms and Protocols
A transform set represents a certain combination of security protocols and algorithms. During IKE negotiation, the peers agree to use a particular transform set for protecting data flow.
During IKE negotiations, the peers search in multiple transform sets for a transform that is the same at both peers. When such a transform set is found, it is selected and applied to the protected traffic as a part of both peers' configurations.
Perform these steps to specify the IPSec transform set and protocols, beginning in global configuration mode:
Purpose | ||
|---|---|---|
Step 1 | crypto ipsec transform-set transform-set-name transform1 [transform2] [transform3] [transform4] Example: | Defines a transform set—an acceptable combination of IPSec security protocols and algorithms. See the Cisco IOS Security Command Reference for detail about the valid transforms and combinations. |
Step 2 | crypto ipsec security-association lifetime {secondsseconds | kilobyteskilobytes} Example: | Specifies global lifetime values used when IPSec security associations are negotiated. See the Cisco IOS Security Command Reference for details. |
Note With manually established security associations, there is no negotiation with the peer, and both sides must specify the same transform set.
Configure the IPSec Crypto Method and Parameters
A dynamic crypto map policy processes negotiation requests for new security associations from remote IPSec peers, even if the router does not know all the crypto map parameters (for example, IP address).
Perform these steps to configure the IPSec crypto method, beginning in global configuration mode:
Purpose | ||
|---|---|---|
Step 1 | crypto dynamic-mapdynamic-map-name dynamic-seq-num Example: | Creates a dynamic crypto map entry and enters crypto map configuration mode. See the Cisco IOS Security Command Reference for more detail about this command. |
Step 2 | set transform-set transform-set-name [transform-set-name2...transform-set-name6] Example: | Specifies which transform sets can be used with the crypto map entry. |
Step 3 | reverse-route Example: | Creates source proxy information for the crypto map entry. See the Cisco IOS Security Command Reference for details. |
Step 4 | exit Example: | Returns to global configuration mode. |
Step 5 | crypto map map-name seq-num [ipsec-isakmp] [dynamicdynamic-map-name] [discover] [profileprofile-name] Example: | Creates a crypto map profile. |
Apply the Crypto Map to the Physical Interface
The crypto maps must be applied to each interface through which IP Security (IPSec) traffic flows. Applying the crypto map to the physical interface instructs the router to evaluate all the traffic against the security associations database. With the default configurations, the router provides secure connectivity by encrypting the traffic sent between remote sites. However, the public interface still allows the rest of the traffic to pass and provides connectivity to the Internet.
Cisco Asa Easy Vpn Server Configuration
Perform these steps to apply a crypto map to an interface, beginning in global configuration mode:
Cisco Easy Vpn Servers
Purpose | ||
|---|---|---|
Step 1 | interface type number Example: | Enters the interface configuration mode for the interface to which you want the crypto map applied. |
Step 2 | crypto map map-name Example: | Applies the crypto map to the interface. See the Cisco IOS Security Command Reference for more detail about this command. |
Step 3 | exit Example: | Returns to global configuration mode. |
Create an Easy VPN Remote Configuration
The router acting as the IPSec remote router must create an Easy VPN remote configuration and assign it to the outgoing interface.
Perform these steps to create the remote configuration, beginning in global configuration mode:
Purpose | ||
|---|---|---|
Step 1 | crypto ipsec client ezvpnname Example: | Creates a Cisco Easy VPN remote configuration, and enters Cisco Easy VPN remote configuration mode. |
Step 2 | group group-name key group-key Example: | Specifies the IPSec group and IPSec key value for the VPN connection. |
Step 3 | peer {ipaddress | hostname} Example: | Specifies the peer IP address or hostname for the VPN connection. Note A hostname can be specified only when the router has a DNS server available for hostname resolution. |
Step 4 | mode {client | network-extension | network extension plus} Example: | Specifies the VPN mode of operation. |
Step 5 | exit Example: | Returns to global configuration mode. |
Step 6 | interfacetype number Example: | Enters the interface configuration mode for the interface to which you want the Cisco Easy VPN remote configuration applied. Note For routers with an ATM WAN interface, this command would be interface atm 0. |
Step 7 | crypto ipsec client ezvpn name [outside | inside] Example: | Assigns the Cisco Easy VPN remote configuration to the WAN interface, causing the router to automatically create the NAT or port address translation (PAT) and access list configuration needed for the VPN connection. |
Step 8 | exit Example: | Returns to global configuration mode. |
Verifying Your Easy VPN Configuration
Configuration Example
The following configuration example shows a portion of the configuration file for the VPN and IPSec tunnel described in this chapter.