Mostly as a reminder to myself, here’s how to set up a Cisco 877 as a “dumb” ADSL modem in PPPoE bridging mode.
The above is very simple to do, but if you only do that you lose the ability to access (via telnet or SSH) your Cisco over the network. That’s not nice, as serial cables are for emergency use only and you don’t want to fire up the terminal emulator just to check your sync speed. So here I’ve used IOS’ integrated routing and bridging mode, or short IRB.
!!! Cisco 877 as ADSL PPPoA to PPPoE bridge (with management IP) ! version 12.4 no service pad service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname modem ip domain name sdfjkl.org ! boot-start-marker boot-end-marker ! logging buffered 4096 informational enable secret 5 NotMyPassword ! aaa new-model aaa authentication login local_auth local username admin privilege 15 secret 5 NotMyPasswordEither ! ! dot11 syslog no ip cef ! ! ! ! archive log config hidekeys ! ! ip ssh version 2 ! !! enable integrated bridging and routing mode to permit management IP whilst bridging PPP bridge irb ! ! interface ATM0 no ip address no atm ilmi-keepalive pvc 0/38 encapsulation aal5snap ! dsl operating-mode auto bridge-group 1 ! ! interface Vlan1 no ip address bridge-group 1 ! !! The bridge virtual interface gets the management IP interface BVI1 ip address 192.168.2.1 255.255.255.0 ! ip default-gateway 192.168.2.2 ip forward-protocol nd ! no ip http server no ip http secure-server ! ! ! control-plane ! !! essential for BVI to work bridge 1 protocol ieee bridge 1 route ip ! line con 0 no modem enable line aux 0 line vty 0 4 login authentication login_local ! scheduler max-task-time 5000 end
The key components are in bold above. The
bridge irb statement enables IRB mode, then the two
bridge-group 1 lines link ATM0 (DSL) and Vlan1 into a bridge. This automatically creates a bridge group virtual interface named BVI1 on which we can then configure the management IP. That’s pretty much it. You will now get PPPoE frames on the same VLAN on which the Cisco listens for its management IP.