Viper SC+™ IP Router for Licensed Spectrum PN 001-5008-000 Rev. C
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The PLC sends many IP keep-alive messages that are sent on-air. When several PLCs do the same, it is possible that a
good part of the on-air bandwidth is used up by the keep-alive traffic.
We recommend that the Viper be configured in router mode and that the TCP Proxy is enabled. The Viper TCP Proxy
feature will filter-out the TCP/IP keep-alive messages.
It has been recommended to Allen-Bradley and Rockwell Automation to have an option in the PLC settings to disable
keep-alive and have user-selectable keep-alive intervals. This could potentially become available in future releases of
PLC firmware.
PLC Reopens TCP/IP Connection With the Same Source Port
This has been seen on the MicroLogix 1100 and 1400 and on the SLC 5.
When the PLC is restarted, it uses the same TCP/IP connection source port previously used.
Note:
The SLC 5 also uses the same source port for each new connection without PLC restart.
Earlier Viper firmware, when in Router mode and having TCP Proxy enabled, did not allow the new TCP connection to
go through immediately if the same TCP source port was used and if the PLC did not terminate the old connection.
After the old TCP Proxy connection timeout, the new connections are okay.
Starting with Viper firmware v1.10 and Viper SC firmware v3.2 (and continuing forward with Viper SC+) a new
enhancement was added to allow new connection created when using the same source port.
It has been recommended to Allen-Bradley and Rockwell Automation to have the TCP source port randomized when
the unit is restarted. This could potentially become available in future releases of PLC firmware.
PLC Detecting Communication Failure While Viper TCP/IP Filters Keep-Alives
The PLC should not reopen a new connection while the connection for the same remote PLC is still in progress.
This has been seen on MicroLogix 1100 and 1400.
When the MicroLogix PLC sends messages but does not receive response messages, it will still keep the TCP connection
open forever as long as the Viper ACKs the keep-alives. Even if the PLC application reports communication loss at the
PLC application level, the PLC will not open a new connection. This is often a result after having communication issues
with remotes.
New firmware is available from Allen-Bradley for the MicroLogix 1100 and 1400.
Allen-Bradley MicroLogix firmware overview at the time of writing this document
For website downloads:
http://www.ab.com/linked/programmablecontrol/plc/micrologix/downloads.html
MicroLogix 1100 series B
(FRN 4 and above are Series B)
:
MicroLogix 1100 series B before FRN 10 require to be upgraded to FRN 10 (released).
MicroLogix 1400 series A:
MicroLogix 1400 series A before FRN 6 require to be upgraded to FRN 6 or 7 (released).
MicroLogix 1400 series B:
MicroLogix 1400 series B before FRN 11 require to be upgraded to FRN 11 (released).
For other MicroLogix models, please contact Rockwell Automation Technical Support.
