Cisco IOS Dial Technologies Configuration Guide, Release 12.2SR

Configuring Cisco Easy IP

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This chapter describes how to configure the Cisco Easy IP feature. It includes the following main sections:

• Cisco Easy IP Overview
• How to Configure Cisco Easy IP
• Configuration Examples for Cisco Easy IP

To identify the hardware platform or software image information associated with a feature, use the Feature Navigator on Cisco.com to search for information about the feature or refer to the software release notes for a specific release. For more information, see the “Identifying Supported Platforms” section in the “Using Cisco IOS Software” chapter.

For a complete description of the Cisco Easy IP commands in this chapter, refer to the Cisco IOS Dial Technologies Command Reference . To locate documentation of other commands that appear in this chapter, use the command reference master index or search online.

Cisco Easy IP Overview

Cisco Easy IP enables transparent and dynamic IP address allocation for hosts in remote environments using the following functionality:

• Cisco Dynamic Host Configuration Protocol (DHCP) server
• Port Address Translation (PAT), a subset of Network Address Translation (NAT)
• Dynamic PPP/IP Control Protocol (PPP/IPCP) WAN interface IP address negotiation

With the Cisco IOS Easy IP, a Cisco router automatically assigns local IP addresses to remote hosts (such as small office, home office or SOHO routers) using DHCP with the Cisco IOS DHCP server, automatically negotiates its own registered IP address from a central server via PPP/IPCP, and uses PAT functionality to enable all SOHO hosts to access the Internet using a single registered IP address. Because Cisco IOS Easy IP uses existing port-level multiplexed NAT functionality within Cisco IOS software, IP addresses on the remote LAN are invisible to the Internet, making the remote LAN more secure.

Cisco Easy IP provides the following benefits:

• Minimizes Internet access costs for remote offices
• Minimizes configuration requirements on remote access routers
• Enables transparent and dynamic IP address allocation for hosts in remote environments
• Improves network security capabilities at each remote site
• Conserves registered IP addresses
• Maximizes IP address manageability

Figure 1 shows a typical scenario for using the Cisco Easy IP feature.

Figure 1 Telecommuter and Branch Office LANs Using Cisco Easy IP

Steps 1 through 4 show how Cisco Easy IP works:

Step 1 When a SOHO host generates “interesting” traffic (as defined by Access Control Lists) for dialup (first time only), the Easy IP router requests a single registered IP address from the access server at the central site via PPP/IPCP. (See Figure 2.)

Figure 2 Cisco Easy IP Router Requests a Dynamic Global IP Address

Step 2 The central site router replies with a dynamic global address from a local DHCP IP address pool. (See Figure 3.)

Figure 3 Dynamic Global IP Address Delivered to the Cisco Easy IP Router

Step 3 The Cisco Easy IP router uses port-level NAT functionality to automatically create a translation that associates the registered IP address of the WAN interface with the private IP address of the client. (See Figure 4.)

Figure 4 Port-Level NAT Functionality Used for IP Address Translation

Step 4 The remote hosts contain multiple static IP addresses while the Cisco Easy IP router obtains a single registered IP address using PPP/IPCP. The Cisco Easy IP router then creates port-level multiplexed NAT translations between these addresses so that each remote host address (inside private address) is translated to a single external address assigned to the Cisco Easy IP router. This many-to-one address translation is also called port-level multiplexing or PAT. Note that the NAT port-level multiplexing function can be used to conserve global addresses by allowing the remote routers to use one global address for many local addresses. (See Figure 5.)

Figure 5 Multiple Private Internal IP Addresses Bound to a Single Global IP Address

How to Configure Cisco Easy IP

Before using Cisco Easy IP, perform the following tasks:

• Configure the ISDN switch type and service provider identifier (SPID), if using ISDN.
• Configure the static route from LAN to WAN interface.
• Configure the Cisco IOS DHCP server.

For information about configuring ISDN switch types, see the chapter “Setting Up ISDN Basic Rate Service” earlier in this publication. For information about configuring static routes, refer to the chapter “Configuring IP Services” in the Cisco IOS IP Configuration Guide .

The Cisco IOS DHCP server supports both DHCP and BOOTP clients and supports finite and infinite address lease periods. DHCP address binding information is stored on a remote host via remote copy protocol (RCP), FTP, or TFTP. Refer to the Cisco IOS IP Configuration Guide for DHCP configuration instructions.

In its most simple configuration, a Cisco Easy IP router or access server will have a single LAN interface and a single WAN interface. Based on this model, to use Cisco Easy IP you must perform the tasks in the following sections:

• Defining the NAT Pool (Required)
• Configuring the LAN Interface (Required)
• Defining NAT for the LAN Interface (Required)
• Configuring the WAN Interface (Required)
• Enabling PPP/IPCP Negotiation (Required)
• Defining NAT for the Dialer Interface (Required)
• Configuring the Dialer Interface (Required)

For configuration examples, see the section “Configuration Examples for Cisco Easy IP” at the end of this chapter.

Configuration Examples for Cisco Easy IP

The following example shows how to configure BRI interface 0 (shown as interface bri0) to obtain its IP address via PPP/IPCP address negotiation:

The following example shows how to configure an asynchronous interface (interface async1) to obtain its IP address via PPP/IPCP address negotiation: