This sample configuration shows a Cisco 1417 Digital Subscriber Line (DSL) Router connecting to a Cisco 6130 Digital Subscriber Line Access Multiplexer (DSLAM) and terminating on a Cisco 6400 Universal Access Concentrator (UAC). The Cisco 1417 has been configured as a Dynamic Host Configuration Protocol (DHCP) server with PPP over ATM (PPPoA).
The Internet Service Provider (ISP) has given the subscriber a single IP address, 172.18.0.1, for Internet connectivity, but 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 1417. NAT is designed for IP address simplification and conservation, as it enables private IP internetworks that use nonregistered IP addresses to connect to the Internet. NAT operates on a router, usually connecting two networks, and 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. As part of this functionality, NAT can be configured to advertise only one address (172.18.0.1) for the entire network. This provides additional security, effectively hiding the entire internal network behind that address.
NAT has the dual functionality of security and address conservation and is typically implemented in remote access environments. An IP address of 10.0.0.1 will be manually configured on the Ethernet interface of the Cisco 1417. The Cisco 1417 will be configured to act as a DHCP server and will lease IP addresses to local LAN devices attached to its Ethernet network.
The following 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, which 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, which means that the interface is connected to an outside network, such as the Internet.
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There are no specific prerequisites for this document.
The information in this document is based on the software versions below.
Cisco 1417 DSL Router IOS® Software Release 12.1(1.3)T
Cisco 6400 UAC-NRP IOS Software Release 12.0(7)DC
Cisco 6400 UAC-NSP IOS Software Release 12.0(4)DB
Cisco 6130 DSLAM-NI2 IOS Software Release 12.1(1)DA
The information presented in this document was created from devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If you are working in a live network, ensure that you understand the potential impact of any command before using it.
In this section, you are presented with the information to configure the features described in this document.
This document uses the network setup shown in the diagram below.
This document uses the configurations shown below.
Current configuration: ! version 12.1 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! 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 !--- The default gateway is assigned to local devices. ! interface Ethernet0 ip address 10.0.0.1 255.0.0.0 ip nat inside ! interface ATM0 no ip address atm vc-per-vp 4096 no atm ilmi-keepalive pvc 1/44 encapsulation aal5mux ppp dialer dialer pool-member 1 ! interface Dialer0 ip address 172.18.0.1 255.255.0.0 ip nat outside encapsulation ppp dialer pool 1 dialer-group 2 ppp authentication chap callin ppp chap hostname <username> ppp chap password <password> ! ip nat inside source list 1 interface Dialer0 overload ip classless access-list 1 permit 10.0.0.0 0.255.255.255 ip route 0.0.0.0 0.0.0.0 Dialer0 no ip http server ! dialer-list 2 protocol ip permit ! line con 0 end
There is currently no verification procedure available for this configuration.
There is currently no specific troubleshooting information available for this configuration.
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Refer to Cisco Technical Tips Conventions for information on conventions used in this document.