RFC1483 Bridged vs Bridged Mode Only

When connecting my ethernet modem to my smoothwall router/firewall,
could someone please explain, on the modem, what the difference is
between RFC1483 Bridged and Bridged Mode Only?

Which ones can be used in the UK?

You see, I keep coming back to the fact that in the UK, we're PPPoA, but
when you want to connect your modem to your router, you can't specify
PPPoA, it's RFC1483 Bridged, or Bridged Mode Only.

In Bridged Mode Only, we get to use PPPoE to authenticate from our
router, our Linux box, or our Windows XP, as suggested here:
http://www.adslguide.org.uk/hardware...nksysADSL2.asp

So then presumably, rather than connecting by PPPoA, we go by PPPoE
because the computer takes control of the connection.

I've seen references for RFC 1483 - Multiprotocol Encapsulation over ATM.

So then I start to wonder, what does that mean? If we set up in RFC1483,
will the modem convert PPPoE from the router to PPPoA?

Try discussing this with Americans, and they can't quite understand PPPoA.

Cya
Simon

"Simon Dean" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> When connecting my ethernet modem to my smoothwall router/firewall, could
> someone please explain, on the modem, what the difference is between
> RFC1483 Bridged and Bridged Mode Only?
>
> Which ones can be used in the UK?
>
> You see, I keep coming back to the fact that in the UK, we're PPPoA, but
> when you want to connect your modem to your router, you can't specify
> PPPoA, it's RFC1483 Bridged, or Bridged Mode Only.
>
> In Bridged Mode Only, we get to use PPPoE to authenticate from our router,
> our Linux box, or our Windows XP, as suggested here:
> http://www.adslguide.org.uk/hardware...nksysADSL2.asp
>
> So then presumably, rather than connecting by PPPoA, we go by PPPoE
> because the computer takes control of the connection.
>
> I've seen references for RFC 1483 - Multiprotocol Encapsulation over ATM.
>
> So then I start to wonder, what does that mean? If we set up in RFC1483,
> will the modem convert PPPoE from the router to PPPoA?
>
> Try discussing this with Americans, and they can't quite understand PPPoA.
>
> Cya
> Simon
>

Simon - this from a forum

QUOTE

How can I tell if I am using PPPOE or RFC1483?

PPPOE - If your ISP assigned you a username and password; you are using
PPPOE

If your ISP assigned you a public static IP address, Subnet Mask, Default
Gateway and primary and secondary DNS addresses; you are using RFC1483.

Note: If you are not sure please contact your ISP.

UNQUOTE

hope it helps

On Sun, 21 May 2006 15:15:50 +0100, "Christopher"
<(E-Mail Removed)> wrote:

>
>"Simon Dean" <(E-Mail Removed)> wrote in message
>news:(E-Mail Removed)...
>> When connecting my ethernet modem to my smoothwall router/firewall, could
>> someone please explain, on the modem, what the difference is between
>> RFC1483 Bridged and Bridged Mode Only?
>>
>> Which ones can be used in the UK?
>>
>> You see, I keep coming back to the fact that in the UK, we're PPPoA, but
>> when you want to connect your modem to your router, you can't specify
>> PPPoA, it's RFC1483 Bridged, or Bridged Mode Only.
>>
>> In Bridged Mode Only, we get to use PPPoE to authenticate from our router,
>> our Linux box, or our Windows XP, as suggested here:
>> http://www.adslguide.org.uk/hardware...nksysADSL2.asp
>>
>> So then presumably, rather than connecting by PPPoA, we go by PPPoE
>> because the computer takes control of the connection.
>>
>> I've seen references for RFC 1483 - Multiprotocol Encapsulation over ATM.
>>
>> So then I start to wonder, what does that mean? If we set up in RFC1483,
>> will the modem convert PPPoE from the router to PPPoA?
>>
>> Try discussing this with Americans, and they can't quite understand PPPoA.
>>
>> Cya
>> Simon
>>
>
>Simon - this from a forum
>
>QUOTE
>
>How can I tell if I am using PPPOE or RFC1483?
>
>PPPOE - If your ISP assigned you a username and password; you are using
>PPPOE
>
>If your ISP assigned you a public static IP address, Subnet Mask, Default
>Gateway and primary and secondary DNS addresses; you are using RFC1483.
>
>Note: If you are not sure please contact your ISP.
>
>UNQUOTE
>
>hope it helps
>


PPPoE is support in the UK by most ISP's - if you have an ethernet WAN
interfaced router that you want to connect to a DSL Modem so that it
gets the Public IP address you can configure the DSL Modem for
rfc1483 bridging and then configure your Router to use PPPoE (and
enter your DSL login details).

Moonshine wrote:

>
> PPPoE is support in the UK by most ISP's - if you have an ethernet WAN
> interfaced router that you want to connect to a DSL Modem so that it
> gets the Public IP address you can configure the DSL Modem for
> rfc1483 bridging and then configure your Router to use PPPoE (and
> enter your DSL login details).

Hypothetically, assume ISP's only support PPPoA. Would Ethernet modems
still work in either the "RFC1483 Bridged" mode, or "Bridged Mode Only"?

I mean people still come out with stuff like "So as it supports RFC1483
(Bridge mode), you need to set it up in that mode to get it to work. In
bridge mode the modem acts as a protocol converter converting ethernet
into ADSL, this means that the host behind it has to handle all of the
login and IP stuff. "

Converts to ADSL? But is it PPPoA, or PPPoE? After the modem (if UK
ISP's did not support PPPoE), would it really matter? Is it PPPoE
because of the router?

Then there's things like "As far as Smoothwal [my router] is concerned,
there is no difference between PPPoA and PPPoE. It just cares about the
"PPP" (authentication) part, as the "oA" (over ATM) or "oE" (over
Ethernet) is an issue that needs to be handled by the modem/bridge to
which Smoothwall's RED interface is connected"

But then when you setup the modem in Bridged mode, you cannot specify
PPPoA, or PPPoE. So the choice of modes, oA or oE must surely be handled
by the router?

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

Cheers
Simon

On Sun, 21 May 2006 17:07:35 +0100, Simon Dean
<(E-Mail Removed)> wrote:

>Moonshine wrote:
>
>>
>> PPPoE is support in the UK by most ISP's - if you have an ethernet WAN
>> interfaced router that you want to connect to a DSL Modem so that it
>> gets the Public IP address you can configure the DSL Modem for
>> rfc1483 bridging and then configure your Router to use PPPoE (and
>> enter your DSL login details).
>
>Hypothetically, assume ISP's only support PPPoA. Would Ethernet modems
>still work in either the "RFC1483 Bridged" mode, or "Bridged Mode Only"?
>
>I mean people still come out with stuff like "So as it supports RFC1483
>(Bridge mode), you need to set it up in that mode to get it to work. In
>bridge mode the modem acts as a protocol converter converting ethernet
>into ADSL, this means that the host behind it has to handle all of the
>login and IP stuff. "
>
>Converts to ADSL? But is it PPPoA, or PPPoE? After the modem (if UK
>ISP's did not support PPPoE), would it really matter? Is it PPPoE
>because of the router?
>
>Then there's things like "As far as Smoothwal [my router] is concerned,
>there is no difference between PPPoA and PPPoE. It just cares about the
>"PPP" (authentication) part, as the "oA" (over ATM) or "oE" (over
>Ethernet) is an issue that needs to be handled by the modem/bridge to
>which Smoothwall's RED interface is connected"
>
>But then when you setup the modem in Bridged mode, you cannot specify
>PPPoA, or PPPoE. So the choice of modes, oA or oE must surely be handled
>by the router?
>
>And, what's the difference between RFC1483 Bridged, and "Bridged Mode Only".
>
>Cheers
>Simon

The best thing you can do is take a look at a diagram that shows the
various ADSL protocol stack implementations.

http://www2.rad.com/networks/2005/modems/ADSLprst.htm

Hopefully that way you can see where the various bits fit.

Bottom line is that in the UK at the user end PPP must be involved
somewhere for IP address allocation and end user authentication.

If you have 2 devices the functions can be split amongst them so long
as the right stack layering is used.

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.

Moonshine wrote:

>
> The best thing you can do is take a look at a diagram that shows the
> various ADSL protocol stack implementations.
>
> http://www2.rad.com/networks/2005/modems/ADSLprst.htm
>
> Hopefully that way you can see where the various bits fit.
>
> Bottom line is that in the UK at the user end PPP must be involved
> somewhere for IP address allocation and end user authentication.
>
> If you have 2 devices the functions can be split amongst them so long
> as the right stack layering is used.
>

Yup. I get all that.

But in this instance, being in bridged mode, the choice of oA or oE is
decided by the device that does the authentication, in this case, the
router. The PPPoE that's setup in the router, won't get magically
changed by the modem to PPPoA, and it doesn't matter whether RFC1483 or
"Bridged Mode Only" do, they both just pass "PPPoE" across.

Bottom line, Is it physically impossible to have a bridged modem and a
PPPoA connection when the router only does PPPoA??? So if ISP's did not
support PPPoE, I would be stuffed unless I got an integrated router with
PPPoA, or some other router that could do PPPoA through the modem via
Ethernet....

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.

But that's what people suggest.

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.

Cya
Simon

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

> 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.

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.

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.

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. Of which Smoothwall doesn't.

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?

>
> 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? 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.

Cheers
Simon