Wrong MAC address fixed in CERN network setting, now the machine is visible from external network too:

From CERN network (even laptop) can connect by 

ssh -XY dsproto@ds-proto-daq2.cern.ch.  (same password as local account in ds-proto-daq)

From ds-proto-daq can also connect by:

ssh darkside01

That is to say that the two network card are now associated to two different names.. but the "real" name is still darkside01.

(will fix).

 enjoy