[cifs-protocol] BranchCache and SMB2: Questions specific to BranchCache.

Christopher R. Hertel crh at ubiqx.mn.org
Tue May 17 15:20:01 MDT 2011

I have a couple of questions regarding BranchCache and [MS-PCCRC].  As you
know, BranchCache--particularly the Content Information format specified in
[MS-PCCRC]--can be used as an extension to SMB2.

1) In the Content Information structure ([MS-PCCRC:2.3]), there is the
   following field definition:

   dwOffsetInFirstSegment (4 bytes): Number of bytes into the first
     segment within the Content Information data structure at which
     the content range begins.

   I can't make heads nor tails of that description, and the captures I
   have done on the wire typically show that field set to zero.
   Similarly, the examples in section 3 of [MS-PCCRC] show the value of
   this field to be zero.

   The field is 4 bytes in length, so it cannot be an offset into the
   content itself, since content offsets are (should be) 8 bytes (64-bit).

   Please clarify:  What does dwOffsetInFirstSegment actually represent?

2) I am not getting what I expect in the dwReadBytesInLastSegment field.
   This field is defined in [MS-PCCRC:2.3], as follows:

   dwReadBytesInLastSegment (4 bytes): Total number of bytes of the
     content range which lie within the final segment in the Content
     Information data structure.

   It seems to me that this value represents the number of bytes
   of actual content included in the calculation of the final
   Segment block of the Content Information.  That interpretation
   is supported by the examples in section 3.

   In actual captures, however, Windows IIS server returns zero
   (0x00000000) in the dwReadBytesInLastSegment field.

   Is this a documentation bug or is the IIS server returning the
   wrong value?

   This is IIS running on W2K8r2 with fairly up-to-date patches

Looking forward to the replies.


Chris -)-----

"Implementing CIFS - the Common Internet FileSystem" ISBN: 013047116X
Samba Team -- http://www.samba.org/     -)-----   Christopher R. Hertel
jCIFS Team -- http://jcifs.samba.org/   -)-----   ubiqx development, uninq.
ubiqx Team -- http://www.ubiqx.org/     -)-----   crh at ubiqx.mn.org
OnLineBook -- http://ubiqx.org/cifs/    -)-----   crh at ubiqx.org

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