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Chapter 2

Sample Network Deployments

•

Chapter 7, “Configuring VPNs Using an IPSec Tunnel and Generic Routing Encapsulation”

•

Chapter 8, “Configuring a Simple Firewall”

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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 encrypted, filtered, and so forth.

Figure 3-1

shows a typical deployment

scenario with a PPPoE client and NAT configured on the Cisco router.

Figure 3-1

PPP over Ethernet with NAT

2

3

5

6

1

7

4

Internet

1

Multiple networked devices—Desktops, laptop PCs, switches

2

Fast Ethernet LAN interface (inside interface for NAT)

3

PPPoE client—Cisco 851 or Cisco 871 access router

4

Point at which NAT occurs

5

Fast Ethernet WAN interface (outside interface for NAT)

6

Cable modem or other server (for example, a Cisco 6400 server) that is connected to the Internet

7

PPPoE session between the client and a PPPoE server

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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 separate dialer pool.

A PPPoE session is initiated on the client side by the Cisco 850 or Cisco 870 series router.An established

PPPoE client session can be terminated in one of two ways:

•

By entering the

clear vpdn tunnel pppoe

command. The PPPoE client session terminates, and the

PPPoE client immediately tries to reestablish the session. This also occurs if the session has a

timeout.

•

By entering the

no pppoe-client dial-pool

number

command to clear the session. The PPPoE client

does not attempt to reestablish the session.

NAT

NAT (represented as the dashed line at the edge of the Cisco router) signifies two addressing domains

and the inside source address. The source list defines how the packet travels through the network.

Configuration Tasks

Perform the following tasks to configure this network scenario:

•

Configure the Virtual Private Dialup Network Group Number

•

Configure the Fast Ethernet WAN Interfaces

•

Configure the Dialer Interface

•

Configure Network Address Translation

An example showing the results of these configuration tasks is shown in the

“Configuration Example”

section on page 3-8

.

Configure the Virtual Private Dialup Network Group Number

Configuring a virtual private dialup network (VPDN) enables multiple clients to communicate through

the router by way of a single IP address.

Complete the following steps to configure a VPDN, starting from the global configuration mode. See the

“Configure Global Parameters” section on page 1-5

for details about entering this mode.

Command or Action

Purpose

Step 1

vpdn enable

Example:

Router(config)#

vpdn enable

Router(config)#

Enables VPDN on the router.

Step 2

vpdn-group

name

Example:

Router(config)#

vpdn-group 1

Router(config-vpdn)#

Creates and associates a VPDN group with a

customer or VPDN profile.

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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:

Step 3

request-dialin

Example:

Router(config-vpdn)#

request-dialin

Router(config-vpdn-req-in)#

Creates a request-dialin VPDN subgroup,

indicating the dialing direction, and initiates the

tunnel.

Step 4

protocol

{

l2tp

|

pppoe

}

Example:

Router(config-vpdn-req-in)#

protocol pppoe

Router(config-vpdn-req-in)#

Specifies the type of sessions the VPDN subgroup

can establish.

Step 5

exit

Example:

Router(config-vpdn-req-in)#

exit

Router(config-vpdn)#

Exits request-dialin VPDN group configuration.

Step 6

exit

Example:

Router(config-vpdn)#

exit

Router(config)#

Exits VPDN configuration, returning to global

configuration mode.

Command or Action

Purpose

Command

Purpose

Step 1

interface

type number

Example:

Router(config)#

interface fastethernet 4

Router(config-if)#

Enters interface configuration mode for a

Fast Ethernet WAN interface.

Step 2

pppoe-client dial-pool-number

number

Example:

Router(config-if)#

pppoe-client

dial-pool-number 1

Router(config-if)#

Configures the PPPoE client and specifies the

dialer interface to use for cloning.

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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 configured on a Fast Ethernet

interface, but each session must use a separate dialer interface and a separate dialer pool.

Complete the following steps to configure a dialer interface for one of the Fast Ethernet LAN interfaces

on the router, starting in global configuration mode.

Step 3

no shutdown

Example:

Router(config-if)#

no shutdown

Router(config-if)#

Enables the Fast Ethernet interface and the

configuration changes just made to it.

Step 4

exit

Example:

Router(config-if)#

exit

Router(config)#

Exits configuration mode for the Fast Ethernet

interface and returns to global configuration

mode.

Command

Purpose

Command

Purpose

Step 1

interface dialer

dialer-rotary-group-number

Example:

Router(config)#

interface dialer 0

Router(config-if)#

Creates a dialer interface (numbered 0–255), and

enters interface configuration mode.

Step 2

ip address negotiated

Example:

Router(config-if)#

ip address negotiated

Router(config-if)#

Specifies that the IP address for the interface is

obtained through PPP/IPCP (IP Control Protocol)

address negotiation.

Step 3

ip mtu

bytes

Example:

Router(config-if)#

ip mtu 1492

Router(config-if)#

Sets the size of the IP maximum transmission unit

(MTU). The default minimum is 128 bytes. The

maximum for Ethernet is 1492 bytes.

Step 4

encapsulation

encapsulation-type

Example:

Router(config-if)#

encapsulation ppp

Router(config-if)#

Sets the encapsulation type to PPP for the data

packets being transmitted and received.