The H0-ECOMM100 never responded to my incorrectly formated ModbusTCP request.

[harncw]

Granted the error was on my side... (I had my bits and bytes incorrect)
However the ECOMM100 maybe should have responded with something.

Firmware 4.0.269
Booter 4.0.165

From Wireshark:

No.     Time        Source                Destination           Protocol Info
    664 33.178201   192.168.1.109         192.168.1.100         Modbus/TCP    query [ 1 pkt(s)]: trans:     1; unit: 255, func:  15: Force Multiple Coils.

Frame 664: 69 bytes on wire (552 bits), 69 bytes captured (552 bits)
Ethernet II, Src: Intel_4f:a6:32 (00:07:e9:4f:a6:32), Dst: HostEngi_20:e9:db (00:e0:62:20:e9:db)
Internet Protocol, Src: 192.168.1.109 (192.168.1.109), Dst: 192.168.1.100 (192.168.1.100)
Transmission Control Protocol, Src Port: xinuexpansion4 (2024), Dst Port: asa-appl-proto (502), Seq: 1, Ack: 1, Len: 15
Modbus/TCP
    transaction identifier: 1
    protocol identifier: 0
    length: 9
    unit identifier: 255
    Modbus
        function 15:  Force Multiple Coils
        reference number: 3104
        bit count: 24
        byte count: 2
        Data

0000  00 e0 62 20 e9 db 00 07 e9 4f a6 32 08 00 45 00   ..b .....O.2..E.
0010  00 37 79 2e 40 00 80 06 fd 70 c0 a8 01 6d c0 a8   .7y.@....p...m..
0020  01 64 07 e8 01 f6 b6 ec 79 21 1d ec c0 a2 50 18   .d......y!....P.
0030  ff ff 05 cf 00 00 00 01 00 00 00 09 ff 0f 0c 20   ...............
0040  00 18 02 00 00                                    .....

[Greg]

Is this Wireshark trace a sample of the incorrectly formatted telegram your ECOM100 didn't respond to? Or is this a correctly formatted one that it does respond to?

[harncw]

The former.

I'm showing an improper ModBusTCP request, the PLC never responds to this request.
 the bits are 24 and the byte count is 2. (there are typically 8 bits in a byte, not 12)

When I send this bad "telegram" (I guess that term can be used) to the PLC I do not get a response.

I'm not positive I really should get a response to bad request.  However I noticed this as I was debugging my side, and I wanted to point out that when I send this bad request I get no response.

Granted, I should definitely not send bad requests, however maybe when I do, I should get a response?

It's debatable, I just noticed this and wanted to point it out.

[Greg]

Thanks for the heads-up on this. Yes, we discovered we have not been verifying the byte count on FC15 or FC16.  We will add a verification for these. Since this is a hole in our code, send me an e-mail (support@hosteng.com) with shipping address and I'll send you a HOST T-shirt. Specify size. 

[harncw]

Hey cool I just so happen to wear shirts!

I appreciate Host taking this relatively minor issue seriously.  I find that seemingly trivial things can point to valuable information.

Hmm now I'm going to try and break your toy in other ways, maybe I can outfit my whole family in Host T-Shirts!

[Controls Guy]

Hey cool I just so happen to wear shirts!

So YOU'RE the one!   

[b_carlton]

Yeah, I understand. You keep getting thrown out of restaurants then it finally dawns on you what the sign means. I started wearing shoes at that same time.