Re: Request for a new DLT for MTP2 with FCS

[Stephen Donnelly <stephen () endace com>]

As a question to the community in general, is it true that the link
layer checksum is not normally included in libpcap records, and that
only frames with valid L2 checksums are normally captured?

If so it seems clear that DLT_MTP2 (and other) link types should not
have the L2 checksum present appended to their records. Varying from
this practice would cause problems for applications which do not expect
the extra bytes.

If there is a special case for MTP2 where capturing the L2 checksum is
desirable, then I agree that it makes sense to add a new DLT value to
distinguish this.

It would only be necessary to add *_FCS DLTs where people specifically
request the ability to capture the checksum. This would keep the number
of new DLTs required to the minimum.

Regards,
Stephen

On Thu, 2007-02-08 at 19:44 +0100, Florent.Drouin () alcatel-lucent fr
wrote:
> I agree with you, the problem I am speaking about, seems to be a common
> problem.
> It is very difficult to differentiate a frame with FCS (Frame Check
> Sequence) and a frame without, if we are just looking at the linktype.
> But, with the current libpcap, I do not see other solutions, than using
> different linktypes.
>
> Is it really a problem to create new linktypes, just for such purpose ?
> (I understood that the linktypes are coded on 4 bytes )
>
> Regards
> Florent

-- 
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    Stephen Donnelly BCMS PhD           email: sfd () endace com
    Endace Technology Ltd               phone: +64 7 839 0540
    Hamilton, New Zealand               cell:  +64 21 1104378
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