Connect to modbus server from another PC

[dhoomakethu]

Hello,

I am getting back to this code base after a long time and I am trying to connect to Modbus async server (TCP) running on my mac from a linux machine.

I am running the example server_async.py like this and I see the server started.

python3 examples/server_async.py -c tcp -f socket -l debug -p 5020 --slaves 2 
2023-11-03 14:47:21,865 DEBUG logging:103 Awaiting connections server_listener
Executing <Task pending name='Task-1' coro=<async_helper() running at /Users/sanjay/repo/pymodbus/examples/server_async.py:228> wait_for=<_GatheringFuture pending cb=[Task.task_wakeup()] created at /Users/sanjay/.pyenv/versions/3.10.0rc1/lib/python3.10/asyncio/tasks.py:663> cb=[_run_until_complete_cb() at /Users/sanjay/.pyenv/versions/3.10.0rc1/lib/python3.10/asyncio/base_events.py:184] created at /Users/sanjay/.pyenv/versions/3.10.0rc1/lib/python3.10/asyncio/tasks.py:638> took 9.430 seconds
2023-11-03 14:47:21,871 INFO  logging:97 Server listening.

Started a client (again from examples) on the same machine and all seem to work fine.

python3 examples/client_sync.py -c tcp -f socket -l debug -p 5020 --host 192.168.1.6
2023-11-03 14:51:48,421 DEBUG logging:103 Connection to Modbus server established. Socket ('192.168.1.6', 60318)
2023-11-03 14:51:48,421 DEBUG logging:103 Current transaction state - IDLE
2023-11-03 14:51:48,421 DEBUG logging:103 Running transaction 1
2023-11-03 14:51:48,421 DEBUG logging:103 SEND: 0x0 0x1 0x0 0x0 0x0 0x6 0x1 0x1 0x0 0x20 0x0 0x1
2023-11-03 14:51:48,421 DEBUG logging:103 New Transaction state "SENDING"
2023-11-03 14:51:48,421 DEBUG logging:103 Changing transaction state from "SENDING" to "WAITING FOR REPLY"
2023-11-03 14:51:51,228 DEBUG logging:103 Changing transaction state from "WAITING FOR REPLY" to "PROCESSING REPLY"
2023-11-03 14:51:51,228 DEBUG logging:103 RECV: 0x0 0x1 0x0 0x0 0x0 0x4 0x1 0x1 0x1 0x1
2023-11-03 14:51:51,228 DEBUG logging:103 Processing: 0x0 0x1 0x0 0x0 0x0 0x4 0x1 0x1 0x1 0x1
2023-11-03 14:51:51,229 DEBUG logging:103 Factory Response[ReadCoilsResponse': 1]
2023-11-03 14:51:51,229 DEBUG logging:103 Adding transaction 1
2023-11-03 14:51:51,229 DEBUG logging:103 Getting transaction 1
2023-11-03 14:51:51,229 DEBUG logging:103 Changing transaction state from "PROCESSING REPLY" to "TRANSACTION_COMPLETE"
2023-11-03 14:51:51,229 DEBUG logging:103 Current transaction state - TRANSACTION_COMPLETE
2023-11-03 14:51:51,229 DEBUG logging:103 Running transaction 2
2023-11-03 14:51:51,229 DEBUG logging:103 SEND: 0x0 0x2 0x0 0x0 0x0 0x6 0x1 0x3 0x0 0x4 0x0 0x2
2023-11-03 14:51:51,229 DEBUG logging:103 New Transaction state "SENDING"
2023-11-03 14:51:51,229 DEBUG logging:103 Changing transaction state from "SENDING" to "WAITING FOR REPLY"
2023-11-03 14:51:51,231 DEBUG logging:103 Changing transaction state from "WAITING FOR REPLY" to "PROCESSING REPLY"
2023-11-03 14:51:51,231 DEBUG logging:103 RECV: 0x0 0x2 0x0 0x0 0x0 0x7 0x1 0x3 0x4 0x0 0x11 0x0 0x11
2023-11-03 14:51:51,231 DEBUG logging:103 Processing: 0x0 0x2 0x0 0x0 0x0 0x7 0x1 0x3 0x4 0x0 0x11 0x0 0x11
2023-11-03 14:51:51,231 DEBUG logging:103 Factory Response[ReadHoldingRegistersResponse': 3]
2023-11-03 14:51:51,231 DEBUG logging:103 Adding transaction 2
2023-11-03 14:51:51,231 DEBUG logging:103 Getting transaction 2
2023-11-03 14:51:51,232 DEBUG logging:103 Changing transaction state from "PROCESSING REPLY" to "TRANSACTION_COMPLETE"

Tried the same client from a linux machine on the same network and It resulted in Connection error. Am I missing something here? The same happens with the repl server. The local connections works fine but from another PC on the same network is not reaching.

[dhoomakethu]

TCP packets are definitly coming to the host

[janiversen]

You might have a firewall on the macos blocking the incoming packets. Sometimes you need to set the local address if you have multiple interfaces.

I have a mac mini with the newest os and I frequently start the async server there and connect to it from a Raspberry PI with raspbian OS. Since the mac mini is on my internal network it runs with firewall disabled.

I do not remember that I did something special when I did the setup a couple of years ago.

Did you run the wireshark on the mac ? because in that case it runs directly at device driver level, before the firewall.

[dhoomakethu]

I have disabled the firewall. I will poke around some more.

[dhoomakethu]

I got the server working on a linux machine. Still having trouble running on Mac OSX sonoma. I will debug this later when I get more time. Marking this as closed for now.

[janiversen]

just for reference my Mac mini runs Sonoma, without problems. I did have one problem sometime ago, that both wifi and ethernet was enabled so I had to add a local address to bind pymodbus to a specific interface.

[dhoomakethu]

I am running on my macbook pro with out any ethernet interface. I have tried --host "" and --host 0.0.0.0 with out any success. Will try to debug further.