Re: [OPSAWG] draft-gharris-opsawg-pcap.txt --- FCS length description

[Michael Richardson via tcpdump-workers <tcpdump-workers () lists tcpdump org>]

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> From: Michael Richardson <mcr+ietf () sandelman ca>
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> Date: Mon, 21 Dec 2020 23:13:32 -0500
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> Carsten Bormann <cabo () tzi org> wrote:
>     > On 2020-12-22, at 01:31, Michael Richardson <mcr+ietf () sandelman ca> wrote:
>     >>
>     >> #define LT_FCS_LENGTH(x)         (((x) & 0xF0000000) >> 28)
>     >> #define LT_FCS_DATALINK_EXT(x)           ((((x) & 0xF) << 28) | 0x04000000)
>     >>
>     >> this suggests that the FCS length is really only 3 bits
>
>     > 4 bits, really (assuming 32-bit unsigned integers).
>
> The LT_FCS_LENGTH(x) (bit 28) is treated as a flag to say that the thing is there.
> The DATALINK_EXT(x) might be borked here, only accepting odd values, which
> would really be a problem.  I suspect there are bugs here.
>
> - --
> Michael Richardson <mcr+IETF () sandelman ca>   . o O ( IPv6 IøT consulting )
>            Sandelman Software Works Inc, Ottawa and Worldwide
>
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