Re: RFC1483 Bridged vs Bridged Mode Only

On Sun, 21 May 2006 23:19:45 +0100, Simon Dean wrote:

Bob wrote:
On Sun, 21 May 2006 21:04:14 +0100, Simon Dean wrote:


Bob wrote:

On Sun, 21 May 2006 18:07:35 +0100, Simon Dean wrote:



And, what's the difference between RFC1483 Bridged, and "Bridged
Mode Only".


I don't think that any UK ISP uses RFC1483 on ADSL, you want the
other one.





That's what ADSLGuide suggest too. And all indications, as far as I
can tell, suggest that when the modem is put into Bridged Mode,
authentication passes to the router, or in my case smoothwall.
Therefore in my mind, my smoothwall establishes a PPPoE connection. So
ergo (in my mind) physically impossible to obtain a PPPoA connection
when the modem is bridged.


It's really better to think of it as PPPoEoA

PPPoE, over the ATM network?

Which then begs the question, if ISP's didn't support PPPoE, I
couldn't have this setup, because it's physically impossible to do
PPPoA (for this setup)

ADSLGuide also say RFC1483 is irrelevent in the UK. Yet large numbers
of people suggest it. I also don't know what it is, or how it differs
to Bridged Mode Only, of which, there are no docs I can find.

IIRC RFC1483 is just an extra header that's slapped-on the front of the
AAL5 frame and doesn't do much except say: "this is ethernet", which
isn't much use unless there is the possibility it might be something
else.

That explains why it's not much use in the UK then I guess.


When I was recently looking for a modem, I looked into PPPoE and
decided against it. I just found so many problem reports about it. Some
people say that it wouldn't work until the ISP turned it on for them,
someone said Tiscali's support told him they didn't support it at all -
but he still got it to work. Lots of people complained that it's
difficult to get technical support on it, even from good ISPs, the
frontline people often just deny all knowledge of it. There is also the
problem that it's only widely supported because it's a BT feature, if
you move to LLU, or you ISP migrates to LLU, it may fail to work. There
are also hassles with PPPoE and mtu sizes.

Bringing me back to one of the original questions... with the modem in
bridged mode, it functions just like a modem, so I would need my Linux
box to do PPPoA authentication.

Yes

I personally found setting it up rather easy. It's just trying to figure
which bit of it decides on PPPoE or PPPoA and what the different
bridging modes are. As I say, there's some people that say that PPPoE or
PPPoA is decided and handled in the modem, which sounds like balls
because once you set the bridging mode, you don't specify whether you
wana oA or oE so I assert that's handled on the router itself. Why do
things have to be so difficult. then they say "it really doesn't matter
as long as the PPP bit is done". Then why do we have different modes?

You have to run PPP over something. In the US they use mostly ethernet, in
Europe it's mostly ATM. BT added a hybrid version where ppp runs over
ethernet, which in turn runs over their ATM network.

I'm using FreeBSD so I went for an XModem, an Ethernet modem which
terminates PPPoA itself and hands over the public address by DHCP. For
Linux I'd probably go with an internal PCI modem. I think these are
both better solutions.


Ahh. That would be an infamous half bridge solution of sorts? You got a
link for the XModem?

adslnation.co.uk , but there are other similar products

the less things I stick inside the box the better. I don't trust things
like the USB support, and PCI on Linux. sounds like it's asking for
trouble trying to find the right devices that work. But it's always a
possibility.


Bear in mind that the majority of ADSL routers are based on Linux.


.

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