Cisco Router 850 Series Software Configuration Guide

CH A P T E R
 
3-1
Cisco 850 Series and Cisco 870 Series Access Routers Software Configuration Guide
OL-5332-01 
121753
2
3
5
6
1
7
4
3
Configuring PPP over Ethernet with NAT
The Cisco 851 and Cisco 871access routers support  Point-to-Point Protocol over Ethernet (PPPoE) 
clients and network address translation (NAT). 
Multiple PCs can be connected to the LAN behind the  router. Before the traffic from these PCs is sent 
to the PPPoE session, it can be en crypted, filtered, and so forth. 
Figure 3-1...

 
3-2
Cisco 850 Series and Cisco 870 Series Access Routers Software Configuration Guide
OL-5332-01 
Chapter 3      Configuring PPP over Ethernet with NAT
  Configure the Virtual Private Dialup Network Group Number
PPPoE
The PPPoE Client feature on the router provides PPPoE client support on Ethernet interfaces. A dialer 
interface must be used for cloning virtual access. Multiple PPPoE client sessions can be configured on 
an Ethernet interface, but each session must use a separate dialer interface and a...

 
3-3
Cisco 850 Series and Cisco 870 Series Access Routers Software Configuration Guide
OL-5332-01 
Chapter 3      Configuring PPP over Ethernet with NAT
  Configure the Virtual Private Dialup Network Group Number
Step 3request-dialin
Example:
Router(config-vpdn-grp)# request-dialinRouter(config-vpdn-grp)# 
Creates a request-dialin VPDN subgroup, 
indicating the dialing direction, and initiates the 
tunnel.
Step 4initiate to ip ip-address
Example:
Router(config-vpdn-grp)# initiate to 
192.168.1.1...

 
3-4
Cisco 850 Series and Cisco 870 Series Access Routers Software Configuration Guide
OL-5332-01 
Chapter 3      Configuring PPP over Ethernet with NAT
  Configure the Fast Ethernet WAN Interfaces
Configure the Fast Ethernet WAN Interfaces
In this scenario, the PPPoE client (your Cisco  router) communicates over a 10/100 Mbps-Ethernet 
interface on both the inside and the outside. 
Perform these steps to configure the Fast Ethernet  WAN interfaces, starting in global configuration 
mode:...

 
3-5
Cisco 850 Series and Cisco 870 Series Access Routers Software Configuration Guide
OL-5332-01 
Chapter 3      Configuring PPP over Ethernet with NAT
  Configure the Dialer Interface
Configure the Dialer Interface
The dialer interface indicates how to handle traffic from the clients, including, for example, default 
routing information, the encapsulation protocol, and the dialer pool to use. The dialer interface is also 
used for cloning virtual access. Multiple PPPoE client sessions can be...

 
3-6
Cisco 850 Series and Cisco 870 Series Access Routers Software Configuration Guide
OL-5332-01 
Chapter 3      Configuring PPP over Ethernet with NAT
  Configure the Dialer Interface
Step 7dialer-group group-number
Example:
Router(config-if)# dialer group 1Router(config-if)# 
Assigns the dialer interface to a dialer group 
(1–10).
TipUsing a dialer group controls access to 
your router.
Step 8exit
Example:
Router(config-if)# exit
Router(config)# 
Exits the dialer 0 interface configuration.
Step...

 
3-7
Cisco 850 Series and Cisco 870 Series Access Routers Software Configuration Guide
OL-5332-01 
Chapter 3      Configuring PPP over Ethernet with NAT
  Configure Network Address Translation
Configure Network Address Translation
Network Address Translation (NAT) translates packets from addresses that match a standard access list, 
using global addresses allocated by the dialer interface. Packets that enter the router through the inside 
interface, packets sourced from the router, or both are checked...

 
3-8
Cisco 850 Series and Cisco 870 Series Access Routers Software Configuration Guide
OL-5332-01 
Chapter 3      Configuring PPP over Ethernet with NAT
  Configure Network Address Translation
NoteIf you want to use NAT with a virtual-template interface, you must configure a loopback interface. See 
Chapter 1, “Basic Router Configuration,” for information on configuring a loopback interface.
Step 5no shutdown
Example:
Router(config-if)# no shutdownRouter(config-if)# 
Enables the configuration changes...

 
3-9
Cisco 850 Series and Cisco 870 Series Access Routers Software Configuration Guide
OL-5332-01 
Chapter 3      Configuring PPP over Ethernet with NAT
  Configuration Example
For complete information on the NAT commands, see the Cisco IOS Release 12.3 documentation set. 
For more general information on NAT concepts, see 
Appendix B, “Concepts.”
Configuration Example
The following configuration example shows a portion of the configuration file for the PPPoE scenario 
described in this chapter.
The VLAN...

 
3-10
Cisco 850 Series and Cisco 870 Series Access Routers Software Configuration Guide
OL-5332-01 
Chapter 3      Configuring PPP over Ethernet with NAT
  Configuration Example
Verifying Your Configuration
Use the show ip nat statistics command in privileged EXEC mode to verify the PPPoE with NAT 
configuration. You should see verification output similar to the following example:
Router# show ip nat statistics 
Total active translations: 0 (0 static, 0 dynamic; 0 extended)
Outside interfaces:...