Re: [foxboro] FBM232 FDSI Modbus TCP Driver Changing Port numbers
- From: <Yvon.Landriault@xxxxxxxxxxxxxxx>
- To: <foxboro@xxxxxxxxxxxxx>
- Date: Tue, 14 Oct 2014 07:03:40 -0400
Thanks Mike. I hadn't considered port forwarding at the router that would
likely have worked. However, what I decided to do was use a Schneider Ethernet
/ serial gateway which handles all the issues easily.
Yvon.
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx] On
Behalf Of Michael Toecker
Sent: Monday, October 13, 2014 10:19 AM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] FBM232 FDSI Modbus TCP Driver Changing Port numbers
Yvon,
Because of the IP range you quoted (172.X.X.X), it's reasonable to assume
you're going through a router. If the router is a good router, you can
configure something called "port forwarding" on it (Jim Aster spoke about this
in another email). If you're using something from Best Buy, this probably
won't work reliably.
Basically, port forwarding allows an incoming packet on a specific port (i.e.
outgoing TCP/502 from your ECB device) to exit going to another port (i.e.
incoming TCP/7802 to the Schneider device). Once the connection is established,
TCP traffic will flow between the two systems in much the same manner as it
would have before, only the port numbers get changed. A router can't do
anything about the Modbus ID though, that's a Foxboro setting.
Port forwarding is like specifying a forwarding address with the post office;
you give your old and new address and everyone sending you stuff is none the
wiser. I've used port forwarding in control system environments several times
to interface devices on different networks, the same use case I believe you
have.
A change like this needs to be specifically documented somewhere, it's not
going to be obvious to an engineer who is walking down the system that port
forwarding is being done. Ideally, you'd modify the network diagram to show it,
and add a reference in the P&ID showing these modbus points. It's a
configuration setting in the router, not something you would configure in
Foxboro. Additionally, depending on how important this data is, you should
consider a redundant router setup where if one fails the other will pick up the
slack. Setups for redundancy are a bit more tricky and should be designed and
tested accordingly.
There are a couple of issues I've encountered over the years with modbus in
general:
1. A dropped TCP connection due to network issues may cause a timeout on the
DCS while it is being re-established, and may alarm the operator based on your
settings.
2. Some modbus devices have connection limits (5 is a common number). If the
DCS attempts to connect too many times in a short period, the device will stop
accepting connections while it times out. If the DCS keeps hammering it, it
will never recover and will require a reboot. Not sure if you can modify this
setting in Foxboro.
Mike Toecker
On Fri, Oct 3, 2014 at 11:19 AM, <Yvon.Landriault@xxxxxxxxxxxxxxx> wrote:
> Thanks Tom. I appreciate your input. Unfortunately this device is
> more than a gateway and as a result it must use 7802 as the port for
> Modbus. I spoke with Foxboro support and unless I am willing to pay
> for a custom driver, they say I must use port 502 or nothing. It
> would be helpful if the driver was designed to optionally take a port
> number in the DVOPTS parameter of the ECB201 block.
>
> As an alternate I will try a true blue Ethernet / serial gateway that
> supports port 502. Likely give this a shot next week.
>
> Yvon
>
>
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--
Michael Toecker
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Systems (formerly The Foxboro Company). Use the info you obtain here at
your own risks. Read http://www.thecassandraproject.org/disclaimer.html
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