Configuring PPPoE CPE

The following tasks must be completed to configure a CPE router with for PPPoE:

1. Configure the internal and external interfaces.

2. Configure a dialer interface.

3. Configure NAT/PAT.

4. Configure the router to act as a DHCP server.

5. Configure a default route.

First, configure the internal Ethernet interface with an IP address. It will be the default gateway for the users. Also, configure it as the inside interface for NAT.

Do not put an IP address on the external Ethernet interface. Enable PPPoE on it, and assign it to a PPPoE client dialer pool. The final configuration on the two Ethernet interfaces should be similar to that shown in Example 2-1.

Example 2-1 Configuring Ethernet Interfaces for PPPoE

interface FastEthernet0/0 description DSL interface no ip address pppoe enable pppoe-client dial-pool-number 1

interface FastEthernet0/1 description Internal interface ip address 172.16.1.1 255.255.255.0 ip nat inside

If the external interface is ATM, the configuration changes slightly. You must configure the ATM permanent virtual circuit (PVC) information and assign the interface to a PPPoE client dialer pool. Leave the DSL operating mode at its default to auto-detect the correct modulation, as shown in Example 2-2.

Example 2-2 Configuring an ATM Interface for PPPoE

interface ATM1/0 description DSL interface no ip address dsl operating-mode auto pvc 1/100

pppoe-client dial-pool-number 1

Second, configure a dialer interface and assign it to the same dialer pool as the Ethernet interface. Give it a PPP encapsulation and configure the PPP parameters on it. Make it the NAT outside interface. Limit the maximum transmission unit (MTU) size to 1492 bytes, to allow for the PPP and Ethernet headers. Because DSL is an always-on connection, a dialer list is

not required. Your configuration should look similar to Example 2-3. Verify PPP operation with the show ppp session command. You can also debug PPP with the commands debug ppp authentication and debug ppp negotiation.

Example 2-3 Configuring a Dialer Interface for PPPoE

interface Dialerl ip address negotiated ip mtu 1492 ip nat outside encapsulation ppp dialer pool 1 ppp authentication chap ppp chap password dslpass

Next, configure the router to do NAT or PAT. NAT translates one internal address to one external one. PAT can translate multiple internal addresses to one external one. Most residential and SOHO subscribers use PAT. To configure it, identify the traffic that must be translated using an access list. Then tell the router to translate those IP addresses to the IP address of the dialer interface, and to "overload" that external IP address. The overload command causes the router to use PAT. Be sure to designate the inside and outside interfaces (see Example 2-1 for those commands.) PAT configuration is done in global command mode, and shown in Example 2-4.

Verify your NAT/PAT operation with the show ip nat translations command.

oo Example 2-4 Configuring NAT/PAT

Q- access-list 100 permit ip 172.16.1.0 0.0.0.255 any

C ip nat inside source list 100 interface Dialer1 overload

The next task is to configure the router to serve IP addresses to internal hosts. To set up basic DHCP, create a pool of addresses for assigning to clients, specify the clients' default gateway, and import the DNS information obtained from the DSL provider via PPP. Example 2-5 shows what this might look like. On the router, verify IP address assignment using the command show ip dhcp binding. On a Windows-based user computer, verify the IP address using the DOS command ipconfig /all.

Example 2-5 Configuring a Router as a DHCP Server ip dhcp pool Users import all network 172.16.1.0 255.255.255.0 default-router 172.16.1.1

Finally, configure a static default route. It should point to the dialer interface rather than an IP address, as shown in Example 2-6.

Example 2-6 Configuring a Static Default Route ip route 0.0.0.0 0.0.0.0 Dialer1

+1 0

Post a comment