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Chapter 4

Configuring PPP over ATM with NAT

Configure Network Address Translation

Step 4

ip nat

{

inside | outside

}

Example:

Router(config-if)#

ip nat inside

Router(config-if)#

Applies NAT to the Fast Ethernet LAN interface

as the inside interface.

For details about this command and additional

parameters that can be set, as well as information

about enabling static translation, see the

Cisco IOS IP Command Reference, Volume 1 of 4:

Addressing and Services

.

Step 5

no shutdown

Example:

Router(config-if)#

no shutdown

Router(config-if)#

Enables the configuration changes just made to the

Ethernet interface.

Step 6

exit

Example:

Router(config-if)#

exit

Router(config)#

Exits configuration mode for the Fast Ethernet

interface.

Step 7

interface

type number

Example:

Router(config)#

interface atm 0

Router(config-if)#

Enters configuration mode for the ATM WAN

interface (ATM0) to be the outside interface for

NAT.

Step 8

ip nat

{

inside | outside

}

Example:

Router(config-if)#

ip nat outside

Router(config-if)#

Identifies the specified WAN interface as the NAT

outside interface.

For details about this command and additional

parameters that can be set, as well as enabling

static translation, see the

Cisco IOS IP Command

Reference, Volume 1 of 4: Addressing and

Services

.

Step 9

no shutdown

Example:

Router(config-if)#

no shutdown

Router(config-if)#

Enables the configuration changes just made to the

Ethernet interface.

Command

Purpose

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Chapter 4

Configuring PPP over ATM with NAT

Configuration Example

Note

If 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 the loopback interface.

For complete information on 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 a client in the PPPoA

scenario described in this chapter.

The VLAN interface has an IP address of 192.168.1.1 with a subnet mask of 255.255.255.0. NAT is

configured for inside and outside.

Note

Commands marked by “

(default)

” are generated automatically when you run the

show running-config

command.

!

interface Vlan1

ip address 192.168.1.1 255.255.255.0

ip nat inside

ip virtual-reassembly (

default

)

!

interface ATM0

no ip address

ip nat outside

ip virtual-reassembly

no atm ilmi-keepalive

pvc 8/35

encapsulation aal5mux ppp dialer

dialer pool-member 1

!

dsl operating-mode auto

!

Step 10

exit

Example:

Router(config-if)#

exit

Router(config)#

Exits configuration mode for the ATM interface.

Step 11

access-list

access-list-number

{

deny

|

permit

}

source

[

source-wildcard

]

Example:

Router(config)#

access-list 1

permit

192.168.1.0 255.255.255.0

Defines a standard access list permitting addresses

that need translation.

Note

All other addresses are implicitly denied.

Command

Purpose

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Chapter 4

Configuring PPP over ATM with NAT

Configuration Example

interface Dialer0

ip address negotiated

ip mtu 1492

encapsulation ppp

dialer pool 1

dialer-group 1

ppp authentication chap

!

ip classless (

default

)

!

ip nat pool pool1 192.168.1.0 192.168.2.0 netmask 0.0.0.255

ip nat inside source list 1 interface Dialer0 overload

!

access-list 1 permit 192.168.1.0 0.0.0.255

dialer-list 1 protocol ip permit

ip route 10.10.25.2 0.255.255.255 dialer 0

!

Verifying Your Configuration

Use the

show ip nat statistics

command in privileged EXEC mode to verify the PPPoA client 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:

ATM0

Inside interfaces:

Vlan1

Hits: 0

Misses: 0

CEF Translated packets: 0, CEF Punted packets: 0

Expired translations: 0

Dynamic mappings:

-- Inside Source

[Id: 1] access-list 1 interface Dialer0 refcount 0

Queued Packets: 0

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5

Configuring a LAN with DHCP and VLANs

The Cisco 870 series routers support clients on both physical LANs and virtual LANs (VLANs). The

routers can use the Dynamic Host Configuration Protocol (DHCP) to enable automatic assignment of IP

configurations for nodes on these networks.

Figure 5-1

shows a typical deployment scenario with two physical LANs connected by the router and

two VLANs.

Figure 5-1

Physical and Virtual LANs with DHCP Configured on the Cisco Router

1

2

3

4

1

Fast Ethernet LAN (with multiple networked devices)

2

Router and DHCP server—Cisco 870 series access router—connected to the Internet

3

VLAN 1

4

VLAN 2

DHCP

DHCP, which is described in RFC 2131, uses a client/server model for address allocation. As an

administrator, you can configure your Cisco 800 series router to act as a DHCP server, providing IP

address assignment and other TCP/IP-oriented configuration information to your workstations. DHCP

frees you from having to manually assign an IP address to each client.

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Chapter 5

Configuring a LAN with DHCP and VLANs

Configure DHCP

When you configure a DHCP server, you must configure the server properties, policies, and DHCP

options.

Note

Whenever you change server properties, you must reload the server with the configuration data from the

Network Registrar database.

VLANs

The Cisco 870 series access routers support four Fast Ethernet ports on which you can configure

VLANs.

VLANs enable networks to be segmented and formed into logical groups of users, regardless of the

user’s physical location or LAN connection.

Configuration Tasks

Perform the following tasks to configure this network scenario:

•

Configure DHCP

•

Configure VLANs

Note

The procedures in this chapter assume you have already configured basic router features as well as

PPPoE or PPPoA with NAT. If you have not performed these configurations tasks, see

Chapter 1, “Basic

Router Configuration,” Chapter 3, “Configuring PPP over Ethernet with NAT,”

and

Chapter 4,

“Configuring PPP over ATM with NAT”

as appropriate for your router.

Configure DHCP

Perform these steps to configure your router for DHCP operation, beginning in global configuration

mode:

Command

Purpose

Step 1

ip domain name

name

Example:

Router(config)#

ip domain name smallbiz.com

Router(config)#

Identifies the default domain that the router uses to

complete unqualified hostnames (names without a

dotted-decimal domain name).

Step 2

ip name-server

server-address1

[

server-address2...server-address6

]

Example:

Router(config)#

ip name-server 192.168.11.12

Router(config)#

Specifies the address of one or more Domain Name

System (DNS) servers to use for name and address

resolution.