Cisco SOHO 70 Series Routers

Document ID: 12920

Contents

Introduction
Prerequisites
      Requirements
      Components Used
      Conventions
Configure
      Network Diagram
      Configurations
Verify
Troubleshoot
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Related Information

Introduction

This document shows a Cisco SOHO77 digital subscriber line (DSL) Router that connects to a Cisco 6130 digital subscriber line access multiplexer (DSLAM) and terminates on a Cisco 6400 Universal Access Concentrator (UAC). The Cisco SOHO77 is configured as a Dynamic Host Configuration Protocol (DHCP) server with PPP over ATM (PPPoA).

The ISP has given the subscriber a single IP address, 172.18.0.1, for Internet connectivity. However, the subscriber has a small network of PCs and wants to have Internet access for all devices.

The solution is to configure Network Address Translation (NAT) on the Cisco SOHO77. NAT is designed for IP address simplification and conservation. It enables private IP internetworks that use non-registered IP addresses to connect to the Internet. NAT operates on a router and connects two networks. It translates the private (in this case the 10.0.0.0 network) addresses in the internal network to legal (in this case 172.18.0.1) addresses before packets are forwarded to another network. NAT is configured to advertise only one address (172.18.0.1) for the entire network. This provides additional security. It hides the entire internal network behind that address.

NAT has the dual functionality of security and address conservation. It is implemented in remote access environments. An IP address of 10.0.0.1 is manually configured on the Ethernet interface of the Cisco SOHO77. The Cisco SOHO77 is configured to act as a DHCP server. It leases IP addresses to local LAN devices attached to its Ethernet network.

This configuration shows NAT configured for the Ethernet and ATM interfaces. The Ethernet0 interface has an IP address of 10.0.0.1 with a subnet mask of 255.0.0.0. NAT is configured for inside. This means that the interface is connected to the inside network that is subject to NAT translation. The ATM interface "Dialer0" has an IP address of 172.18.0.1 and a subnet mask of 255.255.0.0. NAT is configured for outside. This means that the interface is connected to an outside network, such as the Internet.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

The information in this document is based on these software and hardware versions:

• Cisco SOHO77 Customer Premises Equipment (CPE) IOS® Software Release 12.1(3)XP2

• Cisco 6400 UAC-Node Route Processor (NRP) IOS Software Release 12.1(3)DC1

• Cisco 6400 UAC-Node Switch Processor (NSP) IOS Software Release 12.1(3)DB

• Cisco 6130 DSLAM-NI2 IOS Software Release 12.1(5)DA

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.

Conventions

For more information on document conventions, refer to the Cisco Technical Tips Conventions.

Configure

In this section, you are presented with the information to configure the features described in this document.

Note: To find additional information on the commands used in this document, use the Command Lookup Tool ( registered customers only) .

Network Diagram

This document uses the network setup shown in this diagram.

Configurations

This document uses this configuration .

! 
version 12.1
service timestamps debug datetime msec 
service timestamps datetime msec 
! 
hostname R1 
! 
ip subnet-zero 
! 
ip dhcp excluded-address 10.0.0.1

!--- The DHCP pool  does not lease this address; it is used by interface E0.

!
ip dhcp pool 
<pool name>

 network 10.0.0.0 255.0.0.0
 default-router 10.0.0.1
 
!--- Default gateway  is assigned to local devices.

! 
interface Ethernet0 
 ip address 10.0.0.1 255.0.0.0 
 no ip directed-broadcast 
 ip nat inside
 no ip mroute-cache
! 
interface ATM0 
 no ip address 
 no ip directed-broadcast 
 no ip mroute-cache 
 no atm ilmi-keepalive
 pvc 1/150 
  encapsulation aal5mux ppp dialer 
  dialer pool-member 1 
 !
 hold-queue 224 in 
! 
interface Dialer0 
  ip address 172.18.0.1 255.255.0.0    
  ip nat outside     
  no ip directed-broadcast 
  encapsulation ppp 
  dialer pool 1 
  dialer-group 2 
  ppp pap sent-username <username> password <password>
! 
ip nat inside source list 1  interface Dialer0 overload 
ip classless 
ip route 0.0.0.0 0.0.0.0 Dialer0 
no ip http server 
! 
access-list 1 permit 10.0.0.0 0.255.255.255 
dialer-list 2 protocol ip permit
! 

end 

Verify

There is currently no verification procedure available for this configuration.

Troubleshoot

There is currently no specific troubleshooting information available for this configuration.

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Related Information

• Cisco DSL Technology Support Information
• Cisco DSL Product Support Information
• Technical Support - Cisco Systems