PPPoE

Answered Question
Mar 12th, 2009

I prepare for ISCW exam, i have some confuse about PPPoE concepts:

- The final before CPE router send PPPoE frame to aggregation router, it have to encapsulate PPPoE frame to ATM ?

- The configuration over the Ethernet Interface, I'm not see any ATM configuration, how CPE router encapsulate PPPoE into ATM frame ?

Thanks

I have this problem too.
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Correct Answer by Giuseppe Larosa about 7 years 9 months ago

Hello Rojer,

- Follow your link if the WAN interface is an Ethernet Interface, the DSL modem will encapsulate Ethernet frame to ATM Cell and send over local loop to CO ?

yes this can be done

- If the WAN Interface is an ATM interface, the DSL modem or other ISP devices is not need ?

yes

Hope to help

Giuseppe

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Giuseppe Larosa Thu, 03/12/2009 - 03:14

Hello Rojer,

1) if the wan interface is an ATM over ADSL the router needs to encapsulate the PPPoE frames inside AAL5 ATM PDUs to send out to the broadand NAS

2) but it is also possible that the WAN interface is an ethernet interface and so you see only the commands to run PPPoE over the ethernet interface.

the pppoE frames can then be sent to an external modem that performs bridging between ethernet and DSL link

3) or it can be a L2 lan based hand-off and no modem is needed

see for case 2

http://www.cisco.com/en/US/tech/tk175/tk15/technologies_configuration_example09186a0080126dc0.shtml

and the reference to config guide

http://www.cisco.com/en/US/docs/ios/bbdsl/configuration/guide/bba_ppoe_client_ps6441_TSD_Products_Configuration_Guide_Chapter.html

Hope to help

Giuseppe

Rojer-bkk Thu, 03/12/2009 - 03:39

Thanks for advice !!

but i have some little point to ask

- Follow your link if the WAN interface is an Ethernet Interface, the DSL modem will encapsulate Ethernet frame to ATM Cell and send over local loop to CO ?

- If the WAN Interface is an ATM interface, the DSL modem or other ISP devices is not need ?

Thanks

Correct Answer
Giuseppe Larosa Thu, 03/12/2009 - 05:59

Hello Rojer,

- Follow your link if the WAN interface is an Ethernet Interface, the DSL modem will encapsulate Ethernet frame to ATM Cell and send over local loop to CO ?

yes this can be done

- If the WAN Interface is an ATM interface, the DSL modem or other ISP devices is not need ?

yes

Hope to help

Giuseppe

Rojer-bkk Fri, 03/13/2009 - 02:39

- why some doc configure pppoe with atm subinterface point-to-point if i configure on atm physical interface, is it not point-to-point connection or it's not correct ?

Giuseppe Larosa Fri, 03/13/2009 - 02:58

Hello Rojer,

atm physical interface is treated as point-to-multipoint your understanding is correct.

Actually, point-to-point subifs can be easier to use they say the associated single vpi/vci is the exit point for everything

Hope to help

Giuseppe

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