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RE: CRC-16 or CRC-32



> -----Original Message-----
> From: linux-ppp-owner@xxxxxxxxxxxxxxx [mailto:linux-ppp-
> owner@xxxxxxxxxxxxxxx] On Behalf Of Milan P. Stanic
> Sent: 20. april 2010 17:10
> To: linux-ppp@xxxxxxxxxxxxxxx
> Subject: Re: CRC-16 or CRC-32
> 
> On Tue, 2010-04-20 at 16:49, Jan Just Keijser wrote:
> > Arne Lie wrote:
> > >Hm, my observations are that if there are bit errors introduced in
> the PPP frame, the "ifconfig ppp0" will count such packets in the
> "error" tab. From this I anticipated that the PPP stack included CRC
> checking of its payload. By CRC-16 I mean 2 byte CRC, CRC-32 4 byte.
> Our customer wants 4 byte CRC. From RFC2823 I see both are mentioned.
> The question is, how does one select either? Perhaps it is not
> configurable via pppd?
> > >
> > RFC2823 is about PPP SDL on SONET/SDH ; AFAIK the pppd code does not
> > support this *at all* so I am not surprised that I did not find any
> > references to CRCs in the headers...
> >
> > So the short answer to your question would be: no, PPP v2.4.5 does
> > not support CRC-16 or CRC-32.
> 
> In Linu CRC is done in kernel ppp driver not the ppp daemon.
> ZLIB compression uses crc-32, AFAIR.
[Arne::] Milan, thanks for your information. Yes, the CRC is done in the kernel part of PPP. My question was how, of possible, one could select CRC-16 or CRC-32 to be activated using options when starting pppd (in a similar manner as one is able to select compression algorithm). In http://fixunix.com/ppp/62264-hdlc-like-framing.html James Carson says that the Solaris implementation of pppd make it possible to negotiate to CRC-32. I read your answer this way: by choosing the deflate compression algorithm, which I believe is using ZLIB, then we *are* using the CRC-32 since it defaults to this.
/Arne
> 
> --
> Kind regards,  Milan
> --------------------------------------------------
> Arvanta, IT Security        http://www.arvanta.net
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