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Date:      Thu, 26 Oct 2000 22:51:00 GMT
From:      "Aaron Hill" <hillaa@hotmail.com>
To:        julian@elischer.org
Cc:        freebsd-questions@FreeBSD.ORG, freebsd-net@FreeBSD.ORG
Subject:   Re: More on PPPoE & ADSL (Telstra Bigpond)
Message-ID:  <F50iFEW6sStwNeKjUbE00001146@hotmail.com>

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>The provider treats these differently
>we probably need to reverse the order of the  Host_uniq and Service
>name fields..

It does look like that hence my searching through the source code to check 
if I could make a simple hack to test it. I ran out of time though.

I've been reading the RFC (2516) lately which says (I quote)...

The PADI packet MUST contain exactly one TAG of TAG_TYPE
Service-Name, indicating the service the Host is requesting, and any number 
of other TAG types.

... so from the order of that statement it seems putting the Service-Name 
tag first is the correct thing to do. The RFC doesn't explicitly mention 
what order the tags should be in.  It's entirely plausible that the ISPs 
equipment has a requirement (bug?) that the service name comes last.

>(I don't know why it comes up with "UTF8" though, I think that's
>TCPDUMP misreading something, (I forget what I put there))

I agree, I think it's tcpdump trying, incorrectly, to interpret the tag 
contents. In case you'd like to see what the Host-Uniq tags actually 
contained here's some hex of the Windows PADI frame...

0:10:5a:0:d3:de Broadcast 8863 60: PPPoE PADI [Host-Uniq UTF8] [Service-Name 
"bigpond"]
0x0000   1109 0000 0015 0103 0006 0010 5a00 d3de        ............Z...
0x0010   0101 0007 6269 6770 6f6e 6400 0000 0000        ....bigpond.....
0x0020   0000 0000 0000 0000 0000 0000 0000             ..............

... and the FreeBSD PADI frame...

0:e0:29:73:81:dd Broadcast 8863 60: PPPoE PADI [Service-Name "bigpond"] 
[Host-Uniq UTF8]
0x0000   1109 0000 0013 0101 0007 6269 6770 6f6e        ..........bigpon
0x0010   6401 0300 0480 7067 c300 0000 0000 0000        d.....pg........
0x0020   0000 0000 0000 0000 0000 0000 0000             ..............

... so Windows' Host-Uniq is "0010 5a00 d3de" and FreeBSD's is "0480 7067 
c3". The RFC states this value can be anything the Host chooses and it is 
not interpreted by the Access Concentrator.

Interestingly the RFC also states that the AC MUST (!) include the Host-Uniq 
value in any PADO/PADS replies, which isn't happening in my capture. So I 
think the AC's PADO continues in another frame which tcpdump isn't showing 
me. This would explain why we don't see the AC-Name tag being sent but 
FreeBSD knows the AC-Name in it's PADR. This is a side issue perhaps, it 
still doesn't explain why the AC doesn't understand FreeBSD's inital PADI.

Sorry if this is information overload or heading down the wrong track. I'm 
just trying to understand the problem.

Aaron

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