IPSec Negotiation/IKE Protocols

This document provides a sample configuration for a virtual tunnel interface (VTI) with IP Security (IPSec). This configuration uses RIP version 2 routing protocol to propagate routes across the VTI. With a VTI, VPN traffic is forwarded to the IPSec virtual tunnel for encryption and then sent out of the physical interface. This sample configuration also demonstrates the use of Cisco Quality of Service with VTIs.

Figure 1. Network Diagram

VIRTUAL TUNNEL INTERFACES

BENEFITS

• Simplifies management---Customers can use the Cisco IOS® Software virtual tunnel constructs to configure an IPSec virtual tunnel interface, thus simplifying VPN configuration complexity, which translates into reduced costs because the need for local IT support is minimized. In addition, existing management applications that can monitor interfaces can be used for monitoring purposes.

• Supports multicast encryption---Customers can use the Cisco IOS Software IPSec VTIs to transfer the multicast traffic, control traffic, or data traffic---for example, many voice and video applications---from one site to another securely.

• Provides a routable interface---Cisco IOS Software IPSec VTIs can support all types of IP routing protocols. Customers can use these VTI capabilities to connect larger office environments---for example, a branch office, complete with a private branch exchange (PBX) extension.

• Improves scaling---IPSec VTIs need fewer established security associations to cover different types of traffic, both unicast and multicast, thus enabling improved scaling.

• Offers flexibility in defining features---An IPSec VTI is an encapsulation within its own interface. This offers flexibility of defining features to run on either the physical or the IPSec interface.

CONFIGURATION SUMMARY

• Dynamic routing---Dynamic routing is used in this configuration to propagate the remote network addresses to the local site. Using dynamic routing simplifies manageability of the IPSec network and enables it to expand without having to manually maintain reach information.

• Quality of service (QoS)---QoS can be used to improve the performance of different applications across the network. In this configuration, traffic shaping is used between the two sites to limit the total amount of traffic that should be transmitted between the two sites. Additionally, the QoS configuration can support any combination of QoS features offered in Cisco IOS Software to support any of the voice, video, or data applications.

Note: The QoS configuration in this guide is for demonstration only . It is expected that the VTI scalability results will be similar to the p2p GRE over IPsec. For scaling and performance considerations please contact your Cisco representative.

LIMITATIONS

• Full security audit on the router. It is recommended that users run a Cisco Router and Security Device Manager (SDM) security audit in wizard mode to lock down and secure the router.

• An initial router configuration step is not shown in the steps. The full configuration is shown in the following section.

• This configuration guide uses private addresses only. When using private addresses and connecting to the Internet, an appropriate Network Address Translation (NAT) or Port Address Translation (PAT) configuration is required to provide connectivity over the Internet.

COMPONENTS USED

• Cisco IOS Software Release 12.3(14)T for the Cisco 3700 Series Multiservice Access Router.

ROUTER CONFIGURATION

Cisco 3745-20 Router Configuration

Cisco 3725-21 Router Configuration

VERIFYING THE RESULTS

Verifying the Status of the Cisco 3745 Router

RELATED INFORMATION

• IPSec Support Page

• An Introduction to IP Security (IPSec) Encryption

• Configuring IPSec Network Security

• Configuring Internet Key Exchange Security Protocol

• Command Lookup Tool (registered customers only)

• Technical Support---Cisco Systems®