Re: PPPoE vs. Bridged ADSL

[Mark Smith <nanog () 85d5b20a518b8f6864949bd940457dc124746ddc nosense org>]

On Wed, 28 Oct 2009 15:33:58 -0700
Walter Keen <walter.keen () rainierconnect net> wrote:

>    Most aDSL modems if set to PPPoE (I think Actiontec's come this way by
>    default) will send the mac as the pppoe un/pw.
>    David E. Smith wrote:
>
> Opinions on this? I'd be interested in hearing the latest real world
> experience for both and the direction most folks are going in.

DOCSIS cable networks use DHCP and have for a long time. If you have
Ethernet based DSLAMs, they can usually do the a number of tricks (e.g.
Option 82 insertion into the DHCP request) that would make a DHCP ADSL
deployment no harder (or easier) than a DOCSIS cable network.

It seems to me that the fundamental purpose of PPPoE is to be able to
uniquely identify the customer for billing/provisioning purposes. Even
though you only need to be able to do that at the start of their
session, with PPPoE you pay an 8 byte per packet overhead, on _every_
packet sent and received by the customer. Other methods of
distinguishing the customer, e.g. Option 82, static DHCP mapped to a
customer MAC address, or possibly 802.1x if it were available, have
much, much lower overhead.

I think PPPoE really only exists to make ADSL look like high speed
dial-up, so that ISPs dial up backend systems didn't need to be changed
when ADSL was introduced. That was a valid concern in the past, but
with existing solutions or models such as the DOCSIS Cable methods, and
Ethernet based DSLAMS, I'd suggest avoiding PPPoE if you can.




> I can't speak to which would be better on copper specifically, but in
>
>
> general I'd favor DHCP over PPPoE. Either way, most of the back-end stuff
> will be similar (you'll need a way to authenticate users, turn them off and
> on, et cetera); the differences won't be all that big. Either you're storing
> their MACs in a database, or their port assignments and VLAN tags, or their
> usernames and passwords.
>
> With PPPoE, however, the end-user can't just plug in and go - they'll have
> to configure their PC, or a DSL modem, or something. That means a phone call
> to your tech support, most likely. In many cases, DHCP can lead to
> plug-and-play simplicity, which means they don't have to call you, and you
> don't have to answer their calls. Everyone wins. :)
>
> David Smith
> MVN.net
>
>
> --
>
>
> Walter Keen
> Network Technician
> Rainier Connect
> (o) 360-832-4024
> (c) 253-302-0194