Is there are risk of errors when setting up a diagnostics
connection via the LAN if the MAC address has been changed
The following information holds for all Industrial Ethernet CPs
whose MAC address (media access control) can be configured with
STEP 7. This module supports the ISO transport protocol amongst
others. Some new CPs do not support the ISO protocol and therefore
it is not possible to configure an MAC address. These modules use
the factory-set MAC address. The defective diagnostics connection
described concerns the following CPs:
- 6GK7 343-1EX10-0XE0 (CP 343-1)
- 6GK7 343-1EX11-0XE0 (CP 343-1)
- 6GK7 443-1EX10-0XE0 (CP 443-1)
- 6GK7 443-1EX11-0XE0 (CP 443-1)
The station and the CP 443-1 have been configured with the
following address parameters:
- IP address: 22.214.171.124
- MAC address: 08.00.06.01.36.01
The station is in RUN. All the modules in the rack are working
perfectly. Now the MAC of the CP is to be changed to
08.00.06.01.36.02. The IP address is retained. The loading
procedure is to be done via the LAN interface (local area network)
with the TCP/IP protocol.
Behavior when loading:
The loading procedure is interrupted temporarily. The dialog
shown in Fig. 1 is displayed. The interruption happens just when
the Industrial Ethernet CP restarts. This happens through receipt
of the new configuration and can be recognized by a brief
RUN-STOP-RUN sequence of the LEDs.
The brief STOP of the module is a standard procedure. Normally the
programming device sets up a new PG channel connection with the IP
address stored in the project. This remains the same, because only
the MAC address has been changed. So the message box depicted below
should not really appear.
Fig 1: Error box, indicating that the target system cannot be
Press the "Details" button to open the following dialog:
Fig. 2: Details of the error box (Fig. 1)
The messages indicate that the programming device could no
longer set up a connection to the module just as the system data
block SDB1003 was supposed to be sent to the CPU. An NCM
diagnostics connection via TCP/IP is no also no longer possible
with this PG.
If you now set up a diagnostics connection to the CP 443-1 via MPI
(MPI address of the CPU and slot of the CP), then the following
figure shows quite clearly that the CP has already adopted the
Fig. 3: NCM S7 diagnostics window
- The whole configuration can be loaded via the MPI
- The whole configuration can be loaded once again from another
PG/PC via the LAN with the TCP/IP protocol.
- The whole configuration can be loaded once again from the same
PG/PC via the LAN with the ISO protocol.
- After a delay of a few minutes – without accessing the
interface used for loading – the loading procedure via TCP
functions again with the same PG.
Always load the configuration changes which include a change of
MAC address via the MPI interface of the associated CPU module.
After starting the first loading procedure the PG first uses
the ARP protocol provided (address resolution protocol) to
determine the MAC address for the IP address 126.96.36.199 which is to
be used for loading. The CP responds with an ARP response with its
MAC address 08.00.06.01.36.01.
The configuration can now be loaded via the TCP/IP protocol.
After restarting of the module however the CP has a different MAC
address. The PG has internally stored an MAC address once
determined as an IP address in the so-called ARP cache.
That is why when setting up a connection again with the PG, the ARP
protocol must no longer be used. Nevertheless the PG is still using
the old MAC address that no longer exists. The proof of this is
provided by the following figure showing the ARP cache of the PG
that has been read out after abortion of the loading process and
subsequent failure of the diagnostics connection via TCP/IP.
Fig. 4: Display of the IP and MAC addresses
The old MAC address is stilled entered for the IP address. This
entry is deleted automatically when the IP address is not used for
a certain period of time by the interface. As a quick remedy here
you can delete individual entries of the ARP cache also in the PG.
Then the ARP protocol is used again when accessing the IP address
and access via TCP/IP is possible.