Siemens ESM - Manual (Page 50)

Interfaces, Displays and Operator Controls
Industrial Ethernet OSM/ESM
46 C79000-Z8976-C068-10
Note
The autocrossover function of a TP/ITP port of the OSM/ESM is active only when it
is set to the autonegotiation mode.
If this is not the case, it may be necessary to replace a straight-through cable with
a crossover cable.
Please remember that even when using straight-through cables, an illegal loop can
occur in the Ethernet network, caused, for example, by connecting two ports on an
OSM/ESM. Such a loop can lead to network overload and network failure.