[cifs-protocol] [REG:111062056241038] SMB1 maximum packet size with signing enabled
George K Colley
gcolley at apple.com
Mon Jun 20 17:17:35 MDT 2011
On Jun 20, 2011, at 3:11 PM, Hongwei Sun wrote:
> Moving Interoperability Documentation Help (dochelp) to bcc.
>
> Hi, all
>
> This is an expected behavior. I have a blog about this topic that should explain the behaviors you have observed (http://blogs.msdn.com/b/openspecification/archive/2009/04/10/smb-maximum-transmit-buffer-size-and-performance-tuning.aspx).
You should update your doc, Reads are not affected.
>
> Jeff,
>
> Please let me know if you have more questions. I can provide you more clarification if needed.
>
> Thanks!
>
>
> --------------------------------------------------------------------
> Hongwei Sun - Sr. Escalation Engineer
> DSC Protocol Team, Microsoft
> hongweis at microsoft.com
> Tel: 469-7757027 x 57027
>
> Exceeding your expectations is my highest priority. If you would like to provide feedback on your case you may contact my manager at allisong at microsoft.com.
>
> ---------------------------------------------------------------------
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>
>
> -----Original Message-----
> From: cifs-protocol-bounces at cifs.org [mailto:cifs-protocol-bounces at cifs.org] On Behalf Of Shirish Pargaonkar
> Sent: Monday, June 20, 2011 4:16 PM
> To: Jeff Layton
> Cc: Interoperability Documentation Help; cifs-protocol at samba.org
> Subject: Re: [cifs-protocol] SMB1 maximum packet size with signing enabled
>
> On Mon, Jun 20, 2011 at 2:56 PM, Jeff Layton <jlayton at samba.org> wrote:
>> On Mon, 20 Jun 2011 11:42:01 -0700
>> George K Colley <gcolley at apple.com> wrote:
>>
>>>
>>> On Jun 20, 2011, at 6:43 AM, Jeff Layton wrote:
>>>
>>>> -----BEGIN PGP SIGNED MESSAGE-----
>>>> Hash: SHA1
>>>>
>>>> I've been doing some testing with signing enabled and have found
>>>> that
>>>> win2k8 seems to consistently return STATUS_ACCESS_DENIED whenever I
>>>> send it a SMB that's larger than 16704 bytes. It seems to have no
>>>> issue with larger sized SMBs when signing is disabled.
>>>>
>>>> It seems sort of like a protocol violation since the NEGOTIATE
>>>> response from the server has the CAP_LARGE_READX and WRITEX bits
>>>> set. It's possible though that I've missed something in the spec.
>>>>
>>>> In any case, my questions:
>>>>
>>>> 1) is this a known limitation in windows, or a bug?
>>> This has been a known issue for a very long time. When signing is on you need to use the negotiated buffer size not the Large CAP size.
>>>>
>>>> 2) is this common to all (most?) versions of windows?
>>> Yes
>>>>
>>>> 3) is there some way we can detect what the server's limit is in this situation?
>>> If the UNIX CAPS is not set and they have signing on then I turn off CAP_LARGE_WRITEX. Note this does not affect CAP_LARGE_READX.
>>>
>>
>> Thanks George...
>>
>> So we need to use the max buffer size advertised by the server? When I
>> look at captures, I can see that the server is sending a max buffer
>> size of 4356 bytes in the NEGOTIATE reply. That's quite a bit smaller
>> than the max size that gives me errors (~16k).
>>
>> Also, I'll note that Shirish looked at some captures between windows
>> and found that sends around 16k packets when signing is negotiated.
>
> In negrprot response (from a Windows 2008 server to a Windows 2003 client), max buffer size is 16634, max raw buffer 65536 and unix extensions not supported, large read andx and large write andx supported.
>
>> I'll bet we can exceed that size by some amount, it would be good
>> though to know how big a size we can get away with...
>>
>> Thanks,
>> --
>> Jeff Layton <jlayton at samba.org>
>> _______________________________________________
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>> cifs-protocol at cifs.org
>> https://lists.samba.org/mailman/listinfo/cifs-protocol
>>
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