Thanks a lot for your very precise answer Jim and Paul,
I haven't thought about HDLC.
It is clear:
PPP frames are packed in HDLC frames just as it happens for every packet
flowing through the Data Link Layer.
So it's normal that they have an HDLC header with address and control field.
Anyway this arises a question of mine:
I read the packets' content by simply doing a printf of the buffer where the
packets are stored inside the ppp source code.
That suggests me that this 2 octects are also added by ppp and not by an
independent hdlc module.
Is that right?
Thanks again.
Ciao da FEDE
-----Urspr�ngliche Nachricht-----
Von: Paul Fulghum <[EMAIL PROTECTED]>
An: Federico Pelizza <[EMAIL PROTECTED]>; linux-ppp
<[EMAIL PROTECTED]>
Datum: Dienstag, 1. Juni 1999 16:25
Betreff: Re: PPP packets
>----- Original Message -----
>From: Federico Pelizza <[EMAIL PROTECTED]>
>To: linux-ppp <[EMAIL PROTECTED]>
>Sent: Thursday, May 27, 1999 9:59 AM
>Subject: PPP packets
>> I'm studying the PPP packets and I encounter something strange in the
>first
>> 2 octets that I transmit in every packet.
>>
>> C0 21 is the LCP protocol field
>> 01 ist the code for ConfReq
>> 01 ist the identifier,
>> etc......
>> but what is FF 03 ?????
>
>The 1st two bytes are the HDLC like address and control field.
>0xFF is the broadcast address.
>0x03 is the unnumbered information (UI) control field.
>
>They don't serve much of a purpose and get stripped once
>address and control field compression (ACFC) LCP option
>is negotiated.
>
>Paul Fulghum [EMAIL PROTECTED]
>Microgate Corporation www.microgate.com
>9501 Capital of Texas Hwy
>Austin, Texas 78759
>(512)-345-7791
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