Setting up PPPoE and overload NAT

Roberto Soto · ‎12-22-2014

Hello Community,

I've been trying to setup a PPPoE session from my home. I own a 871W which is connected from its fastethernet 4 WAN interfaces to a ADLS modem provided by my ISP. I having difficulties understanding the difference betwen my f4 and dialer 0 interface. Where do I apply the overload for example? on f4 or dialer 0? Where do I apply my router default route f4 or dialer 0? If anyone could explain the difference or relationship between these 2 interfaces I will be grateful. Please see configs below, also please note that at the end I posted a PPPoE show output; I dont have a clue if the session is working.

routerA#sh running-config
Building configuration...

Current configuration : 1608 bytes
!
version 12.4
no service pad
service timestamps debug datetime msec
service timestamps log datetime msec
service password-encryption
!
hostname routerA
!
boot-start-marker
boot-end-marker
!
enable secret 5 $1$oEiU$ibFel1m0vRKS8z7AGeEK4.
!
no aaa new-model
!
resource policy
!
ip subnet-zero
ip cef
!
!
no ip domain lookup
!
!
!
username
!
!
!
!
!
interface FastEthernet0
!
interface FastEthernet1
!
interface FastEthernet2
!
interface FastEthernet3 (I've configured switchport access vlan 1 for this interface)
duplex full
speed 100
!
interface FastEthernet4
ip address dhcp
ip nat outside
ip virtual-reassembly
speed 100
full-duplex
pppoe enable group global
pppoe-client dial-pool-number 1
!
interface Dot11Radio0
no ip address
speed basic-1.0 basic-2.0 basic-5.5 6.0 9.0 basic-11.0 12.0 18.0 24.0 36.0 48.0 54.0
station-role root
!
interface Dot11Radio0.10
encapsulation dot1Q 1 native
shutdown
no snmp trap link-status
!
interface Vlan1
ip address 192.168.1.1 255.255.255.0
!
interface Dialer0
ip address negotiated
ip mtu 1492
ip nat outside
ip virtual-reassembly
encapsulation ppp
ip tcp adjust-mss 1452
dialer pool 1
ppp authentication chap callin
ppp chap hostname {myusername}
ppp chap password 7 {mypassword}
!
ip classless
ip route 0.0.0.0 0.0.0.0 Dialer0
!
no ip http server
no ip http secure-server
ip nat inside source list 1 interface Dialer0 overload
!
access-list 1 permit 192.168.1.0 0.0.0.255
no cdp advertise-v2
!
control-plane
!
!
line con 0
logging synchronous
login local
no modem enable
line aux 0
line vty 0 4
login
!
scheduler max-task-time 5000
end

routerA#sh pppoe session
1 client session

Uniq ID PPPoE RemMAC Port VT VA State
SID LocMAC VA-st
N/A 7 d4ca.6d78.317b Fa4 Di0 Vi1 N/A
001c.57f2.3a44 UP

Henrik Grankvist · ‎12-22-2014

Hi

There is no relationship between those two interfaces, they are two different physical interfaces. The cable for the DSL connection is plugged into the dialer interface, while your normal RJ45 connector is plugged in to the fast ethernet interface.

Here is a example config (found here: http://www.cisco.com/c/en/us/tech/long-reach-ethernet-lre-digital-subscriber-line-xdsl/pppoe-pppoa-ppp-over-ethernet-ppp-over-atm/tech-configuration-examples-list.html):

vpdn enable
vpdn-group 1
request-dialin
protocol pppoe
!
interface vlan 1
ip address 192.168.1.1 255.255.255.0
ip nat inside
!
interface dialer 1
ip address negotiated
ppp authentication chap
dialer pool 1
ip nat outside
!
ip nat inside source list 1 interface dialer 1 overload
access-list 1 permit 192.168.1.0 0.0.0.255
!
ip route 0.0.0.0 0.0.0.0 dialer 1

Roberto Soto · ‎12-23-2014

Sorry Henrik I forgot to add that the router is connected via f4 with a RJ45 to a DSL modem. The DSL modem I have no access to. So from the cisco 871w a cable from its wan interfaces (f4) goes to a BT openreach FTTC adsl modem as below.

Henrik Grankvist · ‎12-23-2014

Then you shouldn't worry about the dialer interface, or any of the PPPoE configuration. Just configure the Fa4 as NAT outside and VLAN 1 interface as NAT inside + default route out Fa4.