Hi, thnx for the answer Maaerten,
Στις 18/11/2010 10:36 μμ, ο/η Maarten Litmaath έγραψε:
> Hi Dimitris,
>
>> We have a number of worker nodes behind a linux nat gateway. Recently we
>> have observer that gridftp transfers with multiple streams fails from
>
> Transfers _to_ the WN (downloads) will fail.
>
>> these worker nodes. It seems that in that case the client tells the
>> server to connect to a port with its internal ip address and thus fails:
>> [CLIENT]: PORT 10,210,123,34,95,63
>>
>> Naturally connections to 10.210.123.34 fail.
>>
>> Digging around a bit, it seems that it should be possible to solve this
>> by using GLOBUS_HOSTNAME and setting it to the external ip address for
>> the nat gateway. However it does not seem to work: I am setting
>> GLOBUS_HOSTNAME and then trying a globus-url-copy -p 10 which fails in
>> the same fashion.
>
> How would the NAT gateway know for which WN the connections are intended?
Probably this would require one to one mapping of internal ip addresses
to external, but that defies the purpose of natting in the first place
:). Will just advise users to avoid parallel transfer, and explore FTS.
>
> GridFTP v2 allows this problem to be avoided, but only when both the
> server and the client support it properly:
>
> http://www.ogf.org/documents/GFD.47.pdf
>
> GridFTP v2 is supported by dCache, but not (yet) by the DPM.
>
> Furthermore, globus-url-copy does not fully support it: the code is
> included in Globus/VDT, but the tool does not seem to provide a way
> to let it use "MODE X", which is needed for your scenario to work.
>
> The upshot: one cannot use multiple streams yet for downloading files
> from outside to a machine behind a firewall or a NAT box.
>
Cheers,
--
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Dimitris Zilaskos
GridAUTH Operations Centre @ Aristotle University of Thessaloniki , Greece
Tel: +302310998988 Fax: +302310994309
http://www.grid.auth.gr
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