You are not registered yet. Please click here to register!


 
 
plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
 
Try our online PLC Simulator- FREE.  Click here now to try it.

New Here? Please read this important info!!!


Go Back   PLCS.net - Interactive Q & A > PLCS.net - Interactive Q & A > LIVE PLC Questions And Answers

Reply
 
Thread Tools Display Modes
Old July 30th, 2020, 11:25 AM   #1
TheWaterboy
Lifetime Supporting Member + Moderator
United States

TheWaterboy is offline
 
TheWaterboy's Avatar
 
Join Date: May 2006
Location: State of Denial
Posts: 1,053
Arp traffic over Ethernet radio

Arp traffic is important to switches in a dynamic environment, and not a problem for a high speed network, I understand that.

However when I am using Ethernet over radio and hoping for 19,200 speeds, ARP traffic is clogging the system by taking over a cycle at the expense of other traffic.

It's a polling network and I would like to control when radio comm takes place. This is a completely static IP network like many are, so ARP is not needed to locate changes very often yet the EN2TR and the EN2T modules are pretty chatty so far.

Is there any means to quiet them down?
  Reply With Quote
Old July 30th, 2020, 12:36 PM   #2
drbitboy
Lifetime Supporting Member
United States

drbitboy is offline
 
drbitboy's Avatar
 
Join Date: Dec 2019
Location: Rochester, NY
Posts: 1,236
If the ARP traffic was generated by a linux box, then probably yes


What is the period? Seconds or minutes? PLCs seem to be big on quick discovery, so I suspect the former. If there is nothing in the communication configuration menus, then I suspect firmware is the only solution to quieten the source, probably a non-starter.



What about filtering at the Ethernet "transducer?"
  Reply With Quote
Old July 30th, 2020, 12:38 PM   #3
TheWaterboy
Lifetime Supporting Member + Moderator
United States

TheWaterboy is offline
 
TheWaterboy's Avatar
 
Join Date: May 2006
Location: State of Denial
Posts: 1,053
Transducer ?
  Reply With Quote
Old July 30th, 2020, 12:43 PM   #4
drbitboy
Lifetime Supporting Member
United States

drbitboy is offline
 
drbitboy's Avatar
 
Join Date: Dec 2019
Location: Rochester, NY
Posts: 1,236
Quote:
Originally Posted by TheWaterboy View Post
Transducer ?

LOL, that's why I put it in quotes, it's an analogy to a physical measurement that becomes 0-10V or 4-20ma via a transducer.



What I meant was the conversion from Ethernet level 1 and 2 to whatever the "radio" is.


I don't know what the proper term is. Converter?
  Reply With Quote
Old July 30th, 2020, 12:48 PM   #5
TheWaterboy
Lifetime Supporting Member + Moderator
United States

TheWaterboy is offline
 
TheWaterboy's Avatar
 
Join Date: May 2006
Location: State of Denial
Posts: 1,053
It's an Ethernet radio . . . there is no conversion.
  Reply With Quote
Old July 30th, 2020, 12:51 PM   #6
OkiePC
Lifetime Supporting Member
United States

OkiePC is offline
 
OkiePC's Avatar
 
Join Date: Mar 2005
Location: ENE of Nowhere Oklahoma
Posts: 10,649
Quote:
Originally Posted by TheWaterboy View Post
It's an Ethernet radio . . . there is no conversion.
Make and model?

I seem to recall that you could filter ARP requests on one of the radios I have worked with, but my experience (with Ethernet radio modems) is limited and fading...
__________________
You can choose a ready guide in some celestial voice. If you choose not to decide you still have made a choice.
  Reply With Quote
Old July 30th, 2020, 12:58 PM   #7
drbitboy
Lifetime Supporting Member
United States

drbitboy is offline
 
drbitboy's Avatar
 
Join Date: Dec 2019
Location: Rochester, NY
Posts: 1,236
Quote:
Originally Posted by TheWaterboy View Post
It's an Ethernet radio . . . there is no conversion.

Umm, if you start with cat 5 at 10/100MHz on the PLC, and end up with 19.2kHz over the air, there's gonna be a "transducer." It may be only the physical layer, layer 1, but there is a physical change in the character of the signal.


My point was whatever device makes the conversion might be aware of a layer or two above it and be able to filter out the ARPs. Basically saying the same think OkiePC did.


If the radio doohickey won't oblige, then I think one of the few options would be a purpose-built microcontroller (RaspberryPi?) that acts as a passthrough with a filter that ignores 99.XXX% of the ARP packets coming from the cat 5 side. They are broadcast packets, IIRC, and no one will miss them, as you note.




did you ask The Google summat like this => "ethernet radio" "filter" "arp"


?

Last edited by drbitboy; July 30th, 2020 at 01:08 PM.
  Reply With Quote
Old July 30th, 2020, 01:09 PM   #8
TheWaterboy
Lifetime Supporting Member + Moderator
United States

TheWaterboy is offline
 
TheWaterboy's Avatar
 
Join Date: May 2006
Location: State of Denial
Posts: 1,053
GE MDS Orbit. Brand new.

If this extraneous TCP traffic can't be controlled it really negates the viability of ethernet over radio at low bandwidth. I need the low freq rf here because of topology and that comes with low bandwidth. Really no other option but cellular and thats $$$.

BTW the radios also do serial and that works fantastic (until I put a single Ethernet connection it), but for RTU, serial PLCs that can talk DF1 are becoming a rarity.

Thankfully the 5380 has a serial module that works now so I might have to use only serial, which limits what processors I can use for the polling master. On and On...
  Reply With Quote
Old July 30th, 2020, 01:31 PM   #9
OkiePC
Lifetime Supporting Member
United States

OkiePC is offline
 
OkiePC's Avatar
 
Join Date: Mar 2005
Location: ENE of Nowhere Oklahoma
Posts: 10,649
Quote:
Originally Posted by TheWaterboy View Post
GE MDS Orbit. Brand new.

If this extraneous TCP traffic can't be controlled it really negates the viability of ethernet over radio at low bandwidth. I need the low freq rf here because of topology and that comes with low bandwidth. Really no other option but cellular and thats $$$.

BTW the radios also do serial and that works fantastic (until I put a single Ethernet connection it), but for RTU, serial PLCs that can talk DF1 are becoming a rarity.

Thankfully the 5380 has a serial module that works now so I might have to use only serial, which limits what processors I can use for the polling master. On and On...
I hear you. When the Micrologix 1400 goes bye bye, I am pretty sure we will be switching to Do-More. I must have Modbus RTU support for some legacy gear we support, and I must have RS-232 ports because our two favorite radio systems require it.

I recently gave away a stack of Cal Amp Viper SC modems because there are too many headaches trying to make an Ethernet radio network reliable with them.

I have installed a network of Xeta-4EL that were much better than the Cal Amps, but quite expensive and trying to use that extra Ethernet capability for something like RSLogix over the air...well...it's actually faster to drive 15 miles to plug in than wait on the packets to get sliced and diced and reassembled...They're reliable though except for lightning. If I had that job to do over, I would use serial modems there too. One simple config for all stations, and 1/3 the price.
__________________
You can choose a ready guide in some celestial voice. If you choose not to decide you still have made a choice.
  Reply With Quote
Old July 30th, 2020, 01:38 PM   #10
TheWaterboy
Lifetime Supporting Member + Moderator
United States

TheWaterboy is offline
 
TheWaterboy's Avatar
 
Join Date: May 2006
Location: State of Denial
Posts: 1,053
Quote:
I hear you. When the Micrologix 1400 goes bye bye, I am pretty sure we will be switching to Do-More. I must have Modbus RTU support for some legacy gear we use and must have RS232 ports because our two favorite radio systems require it.
Look at the 5069-L306ER and the 5069-Serial module. It seems AB listened and made DF1 work with only a firmware update. I haven't tested it yet but they make the claim and showed screenshots. I'm pretty sure Modbus RTU was already in there.

I have a couple sets on my desk and a feeling I'll be testing that myself sooner than I expected.

Last edited by TheWaterboy; July 30th, 2020 at 01:39 PM. Reason: typo
  Reply With Quote
Old July 30th, 2020, 01:40 PM   #11
TheWaterboy
Lifetime Supporting Member + Moderator
United States

TheWaterboy is offline
 
TheWaterboy's Avatar
 
Join Date: May 2006
Location: State of Denial
Posts: 1,053
And if they ever upgrade the 1400 to use Logix 5000 they will see a resurgence in popularity. I love that little brick.
  Reply With Quote
Old July 30th, 2020, 02:04 PM   #12
diat150
Lifetime Supporting Member
United States

diat150 is offline
 
Join Date: Mar 2006
Location: Louisiana
Posts: 1,354
seems like the prosoft 900mhz radios were able to handle this. outside of that maybe putting a managed swich or router in between the plc network and the radio would work.
  Reply With Quote
Old July 30th, 2020, 02:24 PM   #13
Ken Roach
Lifetime Supporting Member + Moderator
United States

Ken Roach is online now
 
Ken Roach's Avatar
 
Join Date: Apr 2002
Location: Seattle, WA
Posts: 15,472
Can you quantify "chatty" ?

Do you have a tap/mirror at the master side of this system that you are using the monitor the traffic ?

I just hooked up a tap and Wireshark, and monitored my 1756-ENBT using the filter:

(arp) && (eth.src == 00:00:bc:33:a8:09)

Mine sends out an ARP probe every 122.45 seconds.

Of course ARPs are broadcast packets and every device on the network sends them out periodically. If you've got a router on the network that's providing DHCP addresses to anything, it's probably the most common source of ARP packets.
  Reply With Quote
Old July 30th, 2020, 02:37 PM   #14
diat150
Lifetime Supporting Member
United States

diat150 is offline
 
Join Date: Mar 2006
Location: Louisiana
Posts: 1,354
I wonder if he is talking about multicast?
  Reply With Quote
Old July 30th, 2020, 04:03 PM   #15
Maxkling
Member
United States

Maxkling is offline
 
Join Date: Mar 2011
Location: Atlanta
Posts: 420
Sometimes you can adjust the ARP cache timeout, this is usually done on a switch or device that holds an ARP table. I’ve never known an AB device outside of their switches that allow this adjustment.

I’d love to see a WireShark log of what your are experiencing. I have know AB devices to not handle well erroneous ARP request caused by other devices.

Also network storms are pretty much looping and multiplying ARP requests, I know it would probably cause more havoc than you are describing, but I’ve never seen how this would react with a throughput restriction of a radio in between.

Last edited by Maxkling; July 30th, 2020 at 04:07 PM.
  Reply With Quote
Reply
Jump to Live PLC Question and Answer Forum

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
On Logix5000 system, why there are two or more Ethernet cards on the same rack? wendaiyu LIVE PLC Questions And Answers 17 April 24th, 2016 10:18 PM
UNIGATE CL Ethernet IP Connectivity Issue Hal9000 LIVE PLC Questions And Answers 6 January 11th, 2012 11:28 AM
Ethernet Modbus+ over Radio 15 Miles too much? MesquiteThorn LIVE PLC Questions And Answers 1 January 22nd, 2011 03:53 PM
rslogix 5000 read/write to ethernet radio Stache LIVE PLC Questions And Answers 11 June 21st, 2010 08:04 AM
Using a RADES9300 and serial ethernet to connect to plc...Works over eth but not dial bdoub1eu LIVE PLC Questions And Answers 5 July 28th, 2006 09:30 PM


All times are GMT -4. The time now is 07:27 PM.


.