S7-1512SP-1 PN always falls back to LEGACY

[Erik1000]

Hello, the S7CommPlus communication with my PLC fails:

Here it falls back to LEGACY Put/get (which we want to disable for security reasons)

Fallback

from s7 import Protocol, Client
import logging


logging.basicConfig(level=logging.DEBUG)


client = Client()
client.connect("172.25.250.129", rack=0, slot=1, use_tls=True, protocol=Protocol.AUTO)

data = client.db_read(15, 0, 1)
print(f"db7[0:2] = {data.hex()}")
client.disconnect()

DEBUG:snap7.connection:TCP connected to 172.25.250.129:102
DEBUG:snap7.connection:Sent COTP Connection Request
DEBUG:snap7.connection:Negotiated PDU size: 1024
DEBUG:snap7.connection:Unsupported COTP parameter: code=0xc1, length=2
DEBUG:snap7.connection:Unsupported COTP parameter: code=0xc2, length=16
DEBUG:snap7.connection:Received COTP Connection Confirm
INFO:snap7.connection:Connected to 172.25.250.129:102, PDU size: 1024
DEBUG:s7.connection:=== InitSSL === sending (26 bytes): 72 01 00 12 31 00 00 05 b3 00 00 00 00 00 00 00 00 30 00 00 00 00 72 01 00 00
DEBUG:snap7.connection:Sent 33 bytes: 03 00 00 21 02 f0 80 72 01 00 12 31 00 00 05 b3 00 00 00 00 00 00 00 00 30 00 00 00 00 72 01 00 00
DEBUG:snap7.connection:Received TPKT: version=3 length=31 payload (27 bytes): 02 f0 80 72 01 00 10 32 00 00 05 b3 00 00 00 00 70 00 00 00 00 00 00 72 01 00 00
DEBUG:s7.connection:=== InitSSL === received (24 bytes): 72 01 00 10 32 00 00 05 b3 00 00 00 00 70 00 00 00 00 00 00 72 01 00 00
DEBUG:s7.connection:InitSSL response: version=V1, data_length=16
DEBUG:s7.connection:InitSSL response body (20 bytes): 32 00 00 05 b3 00 00 00 00 70 00 00 00 00 00 00 72 01 00 00
DEBUG:snap7.connection:Sent 1458 bytes: 03 00 05 b2 02 f0 80 16 03 01 05 a6 01 00 05 a2 03 03 e0 95 23 8b 3f ca 90 d1 b6 46 4d 2e ba 72 be 56 f2 65 f2 ee f2 85 2f 45 88 a8 75 12 59 32 53 f2 20 7d 87 64 2b 73 f2 44 db 6f 30 d2 f8 b6 c1 fd f6 40 c0 19 1b 89 f7 68 3a ea d4 4f 97 e1 12 8b 37 00 06 13 02 13 03 13 01 01 00 05 53 00 0b 00 04 03 00 01 02 00 0a 00 12 00 10 11 ec 00 1d 00 17 00 1e 00 18 00 19 01 00 01 01 00 23 00 00 00 16 00 00 00 17 00 00 00 0d 00 2a 00 28 09 05 09 06 09 04 04 03 05 03 06 03 08 07 08 08 08 1a 08 1b 08 1c 08 09 08 0a 08 0b 08 04 08 05 08 06 04 01 05 01 06 01 00 2b 00 03 02 03 04 00 2d 00 02 01 01 00 33 04 ea 04 e8 11 ec 04 c0 4d a4 43 11 32 78 9b 78 75 41 b6 3d 6e a5 ad cc e8 22 cc 13 3c cd cb b7 97 e8 ae c1 18 2d 43 74 a6 1d 52 6d 02 27 14 30 73 59 e6 2c 05 ef cb 41 80 1a 5e a8 c1 02 9e 02 6a b2 5b 97 33 4c 68 e1 60 02 a0 36 0e 87 22 b0 00 22 9f 29 55 28 3e 99 3c f1 37 23 07 dc 05 0e 45 07 7e 85 22 74 44 4c dd 16 b4 0b 65 0e f4 aa 09 14 9b c3 8f 80 bf 5d 6b 1d f6 25 4c 34 34 cc 26 e9 32 8d 0b 52 31 e7 b9 aa c8 9a ef 4b 55 fe 86 5c 8e fc 14 a6 04 4b 29 08 96 a1 e7 12 37 74 ab 54 72 65 24 2c 34 84 c5 98 87 ab 9a 21 1a 9b 89 57 18 4f c6 6f 02 bb 6f 8b 77 5d 52 44 a5 2b c7 c3 e3 0a 69 bd 17 02 bd 70 54 be 6c ae 60 c3 ab 2f 81 4e fb 41 00 99 1a 04 0b a5 16 b8 9a 76 dc 10 84 fb 21 50 41 21 03 5d 6c c8 d9 88 5e 6b 36 48 7b 35 9f bc 85 0f 55 ea 81 7d 71 3d 3d d5 75 77 fa 15 4d d9 be 48 33 74 61 69 65 79 d2 90 67 5a 2a b7 e5 6d fe 88 8c 4b fc 46 e8 f2 92 1c 4a b2 99 7a 90 28 d8 be c5 b8 3d 88 34 cf d9 40 17 2c 30 33 c7 f3 1c c5 a8 95 b1 70 99 b9 d5 cb dd 91 46 24 8c 55 cc 24 9c 02 88 8d 9e 22 89 51 8a 3c f0 44 7d b5 16 25 87 90 3a 8f 1a 0f 00 e7 06 d2 a3 1b e3 ec 62 b4 f0 63 c4 c2 b3 2e d8 c2 f8 a2 08 f4 60 6b c8 49 96 bd 72 bd 89 47 1c d0 e5 99 bd 79 81 ce d1 a0 c3 53 3a 14 12 1a 9e 28 96 92 67 c1 97 58 02 93 e3 ce 7c e5 b7 a5 91 0a 45 33 9b a8 e3 71 aa c2 40 c0 db 88 77 c5 76 1c a8 b9 db 93 c5 cd c8 39 32 47 ca 1b 83 00 16 52 90 6e 94 a6 75 e1 20 30 23 97 26 75 5b 3d 43 13 55 80 67 f8 01 62 0b 37 ae 3e bb 62 d2 c9 35 07 92 35 c9 54 78 22 ba 09 df a0 3a a1 e3 83 31 e0 17 8d 4c 63 8b e4 43 75 7b 17 d0 c7 7b 03 48 67 a4 53 31 d6 73 0f 12 90 29 ca b8 32 86 35 78 31 98 b1 88 a7 a1 88 19 71 21 a5 74 c6 43 6b b9 c7 78 35 79 12 df a1 aa d9 10 c2 53 d3 8c 4c f6 a1 0f f3 00 4f 55 06 f6 ec 5a e0 9b 10 26 e7 36 00 c4 13 9e 26 71 06 db 47 b1 c6 a1 03 6c 79 2d 88 a7 00 61 1c cf 58 bb 04 ba be 21 09 a3 18 5b 63 d0 69 96 a7 6b 45 a0 73 24 88 b9 4c 8b e3 23 cb 2b 09 0b ec 75 36 82 76 16 06 35 ac 87 73 1a b8 7d 81 3a 00 de 11 b2 77 2a 77 40 9c 40 14 23 10 19 19 5c 0c e8 85 92 97 5f a7 92 1f 49 8a 38 d9 6c 02 b6 f8 10 cb e9 9c 64 6a 1a 56 01 1c 43 17 16 06 0c 16 7a 27 c2 85 1c 42 67 d6 0b bf 0b 5c 27 fa 26 db ac 67 85 dc 7e 8d 82 11 b9 80 15 39 67 3b c5 39 39 04 39 7e 8a 43 91 7c fa 2c 45 c0 09 fd 71 c3 19 a5 5a bf e1 89 5c 09 5f d2 f5 7b d5 57 6d 3c 41 27 ca 88 75 b5 f7 61 d8 59 a9 05 1b cf 35 43 7a da 88 b6 db a2 95 af 12 23 8a 94 3c 45 a2 41 54 8c ae 3c 6b 77 a4 0a 5b 28 92 67 35 a7 b5 06 a7 3c c8 d9 cb e7 84 a0 5d 82 5b 76 c2 02 19 5a 10 d3 37 ce 8e c4 47 28 f1 26 be f2 97 88 62 94 f7 f4 6e 71 d7 27 53 45 75 0c 80 9a 66 09 cf e6 c2 4f 5e 58 46 dc 14 ce 90 50 ac 6f 40 ad 21 e1 54 f8 95 3a 54 49 27 d7 59 9b 15 99 81 39 d6 55 27 f3 6a 28 84 c9 b7 12 8c 33 a3 8e 8c 37 c3 93 94 77 76 50 18 c0 44 6d 7e 47 14 eb ec 9b fa b8 7f 95 56 21 07 08 31 92 cb ac 71 c1 8c 5e 84 3b 24 37 08 fd 24 09 f5 eb 11 f4 98 32 fb a0 98 1d 10 47 37 d5 7a 79 43 86 84 a5 3d 6f a0 68 90 c9 a2 eb 22 78 44 15 a4 0b 80 9d 4f 98 c8 47 c5 ae 15 17 a9 90 46 08 9a a2 6e 69 8b 0f da 17 b2 a0 a9 29 6b 01 67 e0 0c 3b 79 7a 2c e5 98 94 f7 cb 39 84 49 11 b2 98 66 e1 1b 1f 87 d6 29 01 c8 b5 0c d8 5f c8 d4 2b bb 32 43 12 b8 91 b4 c4 b9 e6 95 b9 d0 b4 01 b8 13 a7 ac 38 0a 40 e2 7f 92 99 38 37 18 64 d1 96 87 e6 ab 26 3b 56 ac 49 96 1f 65 f1 40 70 d8 3e 21 92 ac 9f cc 5e b5 1b a0 36 a2 6b e7 a5 8e d4 6c 08 a4 35 64 9d 3a c4 6c 09 3b 72 05 78 74 8b 1e de aa 99 97 fa 2e 8a 55 22 8c 99 5e bc 9b 11 5c 4a 7e 0f b8 64 33 56 cf 6b d6 4f 99 c0 0a cd 6a 14 93 57 02 4b f3 9c e8 e7 2f fc 32 32 08 ab 97 a9 07 4b 50 c6 1a 3e 2d 84 bd b4 63 84 4d 34 47 89 0c 9b a9 48 97 36 36 ce 7b 62 a8 e2 3a d7 20 a2 89 1c c7 a7 14 e3 a7 24 22 be 46 4a 46 5d cf 4f e6 63 a5 c4 c7 40 43 15 09 c3 c8 4b 00 1d 00 20 7d 09 95 d8 6a cf b4 22 ca bd 32 9c 2b 28 06 dd 26 79 d0 10 c2 1f fb 2f 5e f0 66 ef b8 a7 c0 4f
INFO:snap7.connection:Disconnected from 172.25.250.129:102
DEBUG:s7.client:S7CommPlus connection failed: Receive error: [WinError 10054] An existing connection was forcibly closed by the remote host
INFO:s7.client:S7CommPlus not available, using legacy S7 for 172.25.250.129:102
INFO:snap7.client:S7Client initialized (pure Python implementation)
DEBUG:snap7.connection:TCP connected to 172.25.250.129:102
DEBUG:snap7.connection:Sent COTP Connection Request
DEBUG:snap7.connection:Negotiated PDU size: 1024
DEBUG:snap7.connection:Unsupported COTP parameter: code=0xc1, length=2
DEBUG:snap7.connection:Unsupported COTP parameter: code=0xc2, length=2
DEBUG:snap7.connection:Received COTP Connection Confirm
INFO:snap7.connection:Connected to 172.25.250.129:102, PDU size: 1024
DEBUG:snap7.connection:Sent 25 bytes: 03 00 00 19 02 f0 80 32 01 00 00 00 01 00 08 00 00 f0 00 00 01 00 01 01 e0
DEBUG:snap7.connection:Received TPKT: version=3 length=27 payload (23 bytes): 02 f0 80 32 03 00 00 00 01 00 08 00 00 00 00 f0 00 00 01 00 01 01 e0
INFO:snap7.client:Negotiated PDU length: 480
INFO:snap7.client:[172.25.250.129 R0/S1] Connected to 172.25.250.129:102 rack 0 slot 1
INFO:snap7.client:Auto-tuned max_parallel=4 (PDU=480)
INFO:s7.client:Legacy S7 connected to 172.25.250.129:102
DEBUG:snap7.connection:Sent 31 bytes: 03 00 00 1f 02 f0 80 32 01 00 00 00 02 00 0e 00 00 04 01 12 0a 10 02 00 01 00 0f 84 00 00 00
DEBUG:snap7.connection:Received TPKT: version=3 length=26 payload (22 bytes): 02 f0 80 32 03 00 00 00 02 00 02 00 05 00 00 04 01 ff 04 00 08 00
DEBUG:snap7.client:[172.25.250.129 R0/S1] db_read db=15 start=0 size=1 (0.8ms)
db7[0:2] = 00
DEBUG:snap7.client:Heartbeat stopped
INFO:snap7.connection:Disconnected from 172.25.250.129:102
INFO:snap7.client:Disconnected from 172.25.250.129:102
DEBUG:snap7.client:Heartbeat stopped
INFO:snap7.client:Disconnected from 172.25.250.129:102

With forced protocol it fails:

from s7 import Protocol, Client
import logging


logging.basicConfig(level=logging.DEBUG)


client = Client()
client.connect(
    "172.25.250.129", rack=0, slot=1, use_tls=True, protocol=Protocol.S7COMMPLUS
)

data = client.db_read(15, 0, 1)
print(f"db7[0:2] = {data.hex()}")
client.disconnect()

DEBUG:snap7.connection:TCP connected to 172.25.250.129:102
DEBUG:snap7.connection:Sent COTP Connection Request
DEBUG:snap7.connection:Negotiated PDU size: 1024
DEBUG:snap7.connection:Unsupported COTP parameter: code=0xc1, length=2
DEBUG:snap7.connection:Unsupported COTP parameter: code=0xc2, length=16
DEBUG:snap7.connection:Received COTP Connection Confirm
INFO:snap7.connection:Connected to 172.25.250.129:102, PDU size: 1024
DEBUG:s7.connection:=== InitSSL === sending (26 bytes): 72 01 00 12 31 00 00 05 b3 00 00 00 00 00 00 00 00 30 00 00 00 00 72 01 00 00
DEBUG:snap7.connection:Sent 33 bytes: 03 00 00 21 02 f0 80 72 01 00 12 31 00 00 05 b3 00 00 00 00 00 00 00 00 30 00 00 00 00 72 01 00 00
DEBUG:snap7.connection:Received TPKT: version=3 length=31 payload (27 bytes): 02 f0 80 72 01 00 10 32 00 00 05 b3 00 00 00 00 70 00 00 00 00 00 00 72 01 00 00
DEBUG:s7.connection:=== InitSSL === received (24 bytes): 72 01 00 10 32 00 00 05 b3 00 00 00 00 70 00 00 00 00 00 00 72 01 00 00
DEBUG:s7.connection:InitSSL response: version=V1, data_length=16
DEBUG:s7.connection:InitSSL response body (20 bytes): 32 00 00 05 b3 00 00 00 00 70 00 00 00 00 00 00 72 01 00 00
DEBUG:snap7.connection:Sent 1458 bytes: 03 00 05 b2 02 f0 80 16 03 01 05 a6 01 00 05 a2 03 03 c2 c5 d8 a6 a3 ce 41 79 93 d0 c5 ed a7 15 d5 5e 20 46 f8 92 ba 24 69 a1 78 63 2a 15 ee dc a7 c9 20 af fe b8 02 4b 58 86 8e ac ae 40 32 34 6f 15 ff 7d 28 12 50 00 b1 5a 31 02 cf 5b fd 67 86 5f 32 00 06 13 02 13 03 13 01 01 00 05 53 00 0b 00 04 03 00 01 02 00 0a 00 12 00 10 11 ec 00 1d 00 17 00 1e 00 18 00 19 01 00 01 01 00 23 00 00 00 16 00 00 00 17 00 00 00 0d 00 2a 00 28 09 05 09 06 09 04 04 03 05 03 06 03 08 07 08 08 08 1a 08 1b 08 1c 08 09 08 0a 08 0b 08 04 08 05 08 06 04 01 05 01 06 01 00 2b 00 03 02 03 04 00 2d 00 02 01 01 00 33 04 ea 04 e8 11 ec 04 c0 24 35 c9 6a cb 74 57 b3 4e dc 14 cd 80 70 72 c7 30 0d fe 0c 2a 12 b3 b2 a2 e6 bf 2f c4 c2 9e f7 16 6f 8c cb 46 65 85 90 54 7c f7 51 b5 37 91 68 1c 87 c7 42 d6 86 62 07 04 5f f5 cd 1e 44 bf 19 f0 4e 2f 1a a8 8a 60 16 37 59 18 29 e3 a8 af 92 0c b9 b1 3c b6 c2 64 52 c8 ac 5f 85 88 45 f1 cd c4 98 7b dd 41 a7 f9 b0 12 3a f1 5c 87 1c 79 c4 08 95 7d a4 7c 83 54 a8 08 e9 6f 7f c7 74 70 20 b4 bd 74 57 59 03 3d 53 f0 01 2a c6 7a ec 02 31 2b 37 a7 f4 e8 b5 48 80 58 a1 bb 35 80 10 2d 99 27 59 86 b7 c1 6e 7a 52 f8 c3 66 58 c6 8c 78 26 75 c2 12 0f 1f 27 5e 53 75 ad 58 f4 85 7c 9b 28 9d 96 61 11 a5 46 35 fb 41 2c 6a 7d 2d f7 2f ac e2 99 4e e5 1a 6f 2a 40 ea b6 5f cb 74 a8 77 08 60 5a 03 39 68 87 9f 30 29 3e 34 c5 69 e4 78 a1 49 5b bc e8 35 30 ed 44 40 d2 e6 c0 27 b6 2f a2 0c be 54 e2 21 f2 0c 1e 22 cc 0e 4b b2 9f a1 f6 1c d4 ea 18 42 c7 4f 6e d4 1f 40 09 a1 6c 76 10 50 61 81 fd 1c a1 47 c0 40 4b c1 92 e1 f2 45 17 0a be e7 b6 77 a8 e4 73 4d a9 4d d0 40 1d 00 67 4f b6 7a 84 ee 7c 60 8d a9 c2 5a ab 3e a6 5b 60 14 83 a3 d3 c3 76 9c 92 71 5c c7 56 76 e7 a7 67 46 80 b1 68 55 e1 59 35 44 b1 8c 69 16 29 8e 45 6b 4e 60 ac 94 a7 1c 9f b4 ba eb c7 28 ec b9 11 11 d7 95 c3 18 79 f9 8a cd ea 59 cb 4e b3 03 3b 5b a2 f8 36 b6 44 a1 c9 05 6c 61 f4 81 76 4c 0b 4e 51 57 a5 29 f0 b7 a0 65 67 ea 1c 70 4b 89 41 ad 0c ab 31 39 77 c9 79 1a 3b 05 2c 7c b8 49 d0 09 7a 3d 4c 17 34 57 1e 82 cc 31 d6 07 3c aa 45 51 30 39 0c d2 a8 20 44 50 a3 55 ea 1c 6a b4 53 60 67 ab 2b ea bb b7 e5 c6 ad 2b 28 1e 46 6a ce c2 a5 c8 42 31 c4 80 38 25 d1 95 45 a5 97 cb c6 6f 90 69 bc 3d 38 ab 07 68 b3 3b c8 0a 49 68 3b c6 5b a9 d7 d5 bd f2 dc 33 cf 38 9b 3c 63 81 e4 35 21 74 8a 95 c0 4a 72 a1 89 45 eb 0c ca 6e c8 9a 1b f7 37 01 a9 0a fc 69 01 71 85 9e a4 83 9c b8 32 0f a3 8b 80 06 4b 9b e8 e0 4a a6 8c 58 d9 bb 8b 58 81 98 15 61 6d 81 19 1d 4c 15 80 dc 15 b4 3b 4b b6 98 e1 a3 38 47 7a e1 45 91 4a b1 3a 64 87 9a 2b 4c 9c 79 48 a2 fe 32 ca d7 f9 1d 96 b8 c3 61 b7 74 4a 70 a7 5e 7c 52 aa 9c b5 e0 75 3e 96 b9 94 8e cc 61 c1 08 cb ef 5a 0e a1 76 b3 4c ea 3a e8 44 a1 60 f0 96 b2 3c 7b 7f 07 2f e0 79 93 dc 42 26 8f d2 88 e4 88 b5 99 20 08 5c 79 c7 36 cb 9b ff 8c a7 71 9a 65 da 36 ae 90 c3 8f 3a b8 5d 26 36 a8 07 30 3b 8f ab 9f 9b f5 7b a6 b0 50 a7 48 5c 6d a0 c6 72 34 c3 3c 54 29 b1 21 50 5c 44 53 0b ca 92 cd 1c 13 e0 77 bf 38 f9 0e 69 83 07 87 63 52 73 89 6d 2b 58 8f 11 ac 65 57 39 34 e5 f2 b9 3a 04 9e 09 c8 44 97 53 ac 1b c1 07 9c d7 38 3a e3 23 70 11 93 e7 55 14 97 62 74 b0 0c 6f 0c 0a 68 81 23 0f 62 f7 85 af e5 ce 51 b6 14 c8 91 23 47 29 78 ec b6 00 d3 6a 7e b8 ec 37 10 95 c1 d5 64 81 2b b7 82 5a 44 a7 9e 89 2c 32 90 4a 27 30 71 ad 64 bf 80 b5 1c 34 bb 5b 74 5a a5 f7 a1 b6 47 12 7e 2a f8 69 ea 67 b4 0d 34 54 79 b8 7c c1 a7 a1 48 bc 17 b7 40 c3 4e 86 b1 a4 03 80 41 04 a4 99 6b 4a 9a 66 a4 ae d3 4f 54 62 58 cc 39 98 fb f0 5a ec 32 93 c8 95 3b e8 37 3e c8 b3 aa a1 db 2d 26 12 c6 de 79 2d 2a 61 7d e1 e6 c0 5e 73 14 b8 42 8c 11 25 05 67 fa 3e 5a a3 21 48 9a 89 54 30 1d 51 ba 3b 02 93 17 9f c8 38 de da 8e eb 78 72 43 19 ab 60 c7 cb ca d8 09 58 12 73 f5 e3 0a ae 71 95 21 80 29 b3 49 1d be 5c 31 1b c8 25 56 94 5a 3e 5a 1a e3 f0 0b 8d 17 15 dd 8a 23 3a 5b b8 3a 56 b4 10 6a af f6 ec 6e 32 97 3f 31 76 c6 fb 09 48 d4 01 86 c8 b8 6c 64 49 99 20 3b 2c 1a 33 4e 54 a7 b8 e9 59 59 15 38 72 bc 3c cb be e9 8c 35 01 a8 7a 87 82 5c 10 17 b4 e2 9f 8c d4 c7 c1 e2 b7 4d e8 ce 37 5a 75 86 45 94 82 55 4d 9e 04 c8 50 68 71 86 22 06 50 3c 7d ea 27 76 29 82 01 44 f1 39 4d 22 3c 25 48 5c 66 0b 2f b2 7e d0 34 32 0c a5 e1 cb e0 74 ea a1 8b 39 39 ad de 22 e2 e0 bd 29 70 01 e1 ed 26 7d 99 5d 00 ea 25 bb dd 4a e5 1c 57 d7 4d a3 33 8e a0 dc 90 51 60 f0 1b 75 41 df 3a cf 73 0c 4b 2f 00 1d 00 20 f2 9c 30 b2 f6 d6 bc 74 b9 86 d3 1e 58 a1 65 dd 9f 83 4f fc 53 c1 a6 5e a8 ad 67 40 b1 6d ff 3f
INFO:snap7.connection:Disconnected from 172.25.250.129:102
DEBUG:s7.client:S7CommPlus connection failed: Receive error: [WinError 10054] An existing connection was forcibly closed by the remote host
Traceback (most recent call last):
  File "<frozen runpy>", line 203, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "X\s7_comm\__main__.py", line 9, in <module>
    client.connect(
    ~~~~~~~~~~~~~~^
        "172.25.250.129", rack=0, slot=1, use_tls=True, protocol=Protocol.S7COMMPLUS
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "X\.venv\Lib\site-packages\s7\client.py", line 124, in connect
    raise RuntimeError(
        f"S7CommPlus connection to {address}:{tcp_port} failed and protocol=S7COMMPLUS was explicitly requested"
    )
RuntimeError: S7CommPlus connection to 172.25.250.129:102 failed and protocol=S7COMMPLUS was explicitly requested

I also tested with #724 but it does not work either.

wireshark.zip

[gijzelaerr]

@Erik1000 This is a known issue that was fixed on master in PR #745 (merged June 18). The TLS ClientHello is being sent directly on the TCP stream instead of being tunneled inside COTP DT frames, which the PLC rejects.

The fix hasn't been released to PyPI yet — you're running from a pip install which has the old ssl.wrap_socket code. To get the fix, install from master:

pip install git+https://github.com/gijzelaerr/python-snap7.git@master

With master, _activate_tls uses ssl.MemoryBIO + ssl.SSLObject to tunnel TLS records through COTP frames, matching what the PLC expects.

Your Wireshark capture confirms this — the PLC sees a raw TLS record where it expects a TPKT/COTP frame and drops the connection.

[Erik1000]

I tested with master

[Erik1000]

… but im on windows sooo maybe that has something to do with it?

[gijzelaerr]

nope, that should be fine. let me see. meanwhile can you double check that you are running the latest master checkout and that you installed that version into your virtual env?

[Erik1000]

nope, that should be fine. let me see. meanwhile can you double check that you are running the latest master checkout and that you installed that version into your virtual env?

@gijzelaerr
sure

uv add git+https://github.com/gijzelaerr/python-snap7.git@master
Resolved 33 packages in 422ms
    Updated https://github.com/gijzelaerr/python-snap7.git (2f06210202ddf59d2c2a03f19e1bc70f3372cc39)
      Built python-snap7 @ git+https://github.com/gijzelaerr/python-snap7.git@2f06210202ddf59d2c2a03f19e1bc70f3372cc39
Prepared 1 package in 8.74s
Installed 1 package in 77ms
 + python-snap7==3.0.0 (from git+https://github.com/gijzelaerr/python-snap7.git@2f06210202ddf59d2c2a03f19e1bc70f3372cc39)

from s7 import Protocol, Client
import logging


logging.basicConfig(level=logging.DEBUG)


client = Client()
client.connect(
    "172.25.250.129",
    password="Mhc123456!",
    rack=0,
    slot=1,
    use_tls=True,
    protocol=Protocol.S7COMMPLUS,
)

data = client.db_read(15, 0, 1)
print(f"db7[0:2] = {data.hex()}")
client.disconnect()

uv run  .
DEBUG:snap7.connection:TCP connected to 172.25.250.129:102
DEBUG:snap7.connection:Sent COTP Connection Request
DEBUG:snap7.connection:Negotiated PDU size: 1024
DEBUG:snap7.connection:Unsupported COTP parameter: code=0xc1, length=2
DEBUG:snap7.connection:Unsupported COTP parameter: code=0xc2, length=16
DEBUG:snap7.connection:Received COTP Connection Confirm
INFO:snap7.connection:Connected to 172.25.250.129:102, PDU size: 1024
DEBUG:s7.connection:=== InitSSL === sending (26 bytes): 72 01 00 12 31 00 00 05 b3 00 00 00 00 00 00 00 00 30 00 00 00 00 72 01 00 00
DEBUG:snap7.connection:Sent 33 bytes: 03 00 00 21 02 f0 80 72 01 00 12 31 00 00 05 b3 00 00 00 00 00 00 00 00 30 00 00 00 00 72 01 00 00
DEBUG:snap7.connection:Received TPKT: version=3 length=31 payload (27 bytes): 02 f0 80 72 01 00 10 32 00 00 05 b3 00 00 00 00 70 00 00 00 00 00 00 72 01 00 00
DEBUG:s7.connection:=== InitSSL === received (24 bytes): 72 01 00 10 32 00 00 05 b3 00 00 00 00 70 00 00 00 00 00 00 72 01 00 00
DEBUG:s7.connection:InitSSL response: version=V1, data_length=16
DEBUG:s7.connection:InitSSL response body (20 bytes): 32 00 00 05 b3 00 00 00 00 70 00 00 00 00 00 00 72 01 00 00
DEBUG:snap7.connection:Sent 1458 bytes: 03 00 05 b2 02 f0 80 16 03 01 05 a6 01 00 05 a2 03 03 53 48 68 a7 16 c6 4a 19 be 50 7d 70 8b 37 22 ca 33 b2 33 63 39 c5 85 76 ef a9 d2 13 28 ca 53 a3 20 ba 02 0e 7f 98 40 f8 b6 3c dc 4d 37 07 80 6c 83 f0 06 ca 6a b4 3e c1 f8 02 b3 56 14 36 17 c7 c9 00 06 13 02 13 03 13 01 01 00 05 53 00 0b 00 04 03 00 01 02 00 0a 00 12 00 10 11 ec 00 1d 00 17 00 1e 00 18 00 19 01 00 01 01 00 23 00 00 00 16 00 00 00 17 00 00 00 0d 00 2a 00 28 09 05 09 06 09 04 04 03 05 03 06 03 08 07 08 08 08 1a 08 1b 08 1c 08 09 08 0a 08 0b 08 04 08 05 08 06 04 01 05 01 06 01 00 2b 00 03 02 03 04 00 2d 00 02 01 01 00 33 04 ea 04 e8 11 ec 04 c0 12 68 48 3e b8 3d 5b 20 34 19 3c 30 3b 24 4d a5 a2 54 d5 80 6d 7a ea 74 82 e4 40 98 86 9f c1 33 71 4d 03 57 47 f3 1a 0f e9 b5 9d 3a 78 f8 62 49 41 94 11 f6 84 35 f4 81 20 de 45 9c db 4a 15 be e0 5d 56 58 7a 8f 8a 6d 18 84 ca c7 d8 ac fc 83 18 40 69 25 34 2a ae 8a 8c 06 56 ec 50 a1 82 8f bf 33 56 c4 f5 6f 36 55 21 84 3a 88 71 21 04 14 0b 21 8d 10 b4 a0 83 a8 b3 24 ac df 17 2b f1 eb 86 43 f6 82 3a bb 06 ad 30 29 fc 5b 3f 51 64 15 91 25 20 e1 43 45 92 d4 70 3a b3 c3 4c 48 7e 26 40 21 ce eb 4d 2f 0c 78 e4 12 cd 4d 00 12 91 e0 88 40 e3 25 8b 56 3d 12 a4 1b 1b a2 6c 89 d8 8d 1b 78 19 9a b0 1a 78 d1 c8 b9 cb c6 18 ec a0 c6 db b5 78 18 cf f1 55 71 a9 76 21 f2 5c b7 c5 c0 5a a0 39 ce bc 16 45 40 e2 77 97 08 8a 14 43 b9 86 e2 a6 06 da b7 ec 05 58 7d 5c 3b 9a d5 73 b5 9c 9c e2 ac b8 ca 39 56 d7 02 2f 5f 16 1c 55 97 bb fd e2 6b 19 dc 6f 5a d5 43 c6 24 88 e4 32 b0 b1 6c 1a fc 62 8b 00 56 99 b2 76 a0 c0 b0 0b ff b6 7b da e5 02 1c 28 ad 21 36 0d a4 68 3f 34 e0 6d 59 21 52 ab 31 b7 7d 28 46 3f 00 c4 17 15 6a 52 13 cc 3a 96 93 e2 61 1b 77 98 aa 4b 52 64 f8 23 94 02 70 ac 1b 54 a7 14 79 46 64 e5 22 8b 75 6a 00 52 61 c5 f4 85 9e dc 00 f5 b1 0a 3a c4 20 4f 1b 3c 9e b2 3d 02 95 3b af fc b3 9b d7 69 79 40 a8 33 86 af 7b da cb 4e 6b 35 ce c6 2b f9 e8 ad c4 ea 03 ca 22 7b dc 3b 15 f3 66 4a 8f f6 95 d8 bb 30 b8 37 64 24 b5 12 36 b0 be ed 5c bd d1 b7 18 18 a5 b2 07 d2 64 5c 4c 99 b2 ac cf 60 36 5e 0f 53 5b 98 89 81 3f d1 20 17 40 12 9d 60 7c 51 75 21 64 90 94 58 d6 07 30 d5 82 bc 57 16 6f b4 1c a3 4a c6 51 93 af 65 f3 72 95 80 6e 2d 57 5d 1e 8c 10 5c 03 3e d0 38 4c 43 f2 ca 62 52 37 82 84 b1 93 b9 be 6c 37 94 8b ea 54 8c 9b 96 86 f5 9e 13 a2 32 45 76 c6 ee 7c 9f 50 b9 68 51 51 02 14 0a 0e f3 26 21 68 e1 68 b9 bc 63 ce 93 b6 a3 ec ab a4 a1 61 47 a7 0a 3a 37 cc ba 06 5a 5e 02 86 7e 16 5b 80 70 76 87 76 96 cd 38 a3 2a c6 79 e8 d8 be 4a 46 22 88 c0 3a f0 c3 c9 11 12 8b 91 95 37 22 88 79 19 54 3e e6 63 55 02 b9 5a 2e a3 b5 5a 61 20 ef 31 a7 9d 07 19 66 56 a1 47 f3 29 4e 48 3c ee b7 c1 39 0a 84 43 b6 a4 73 f1 4a ea ec 53 92 79 68 c9 22 63 e7 18 c8 5a 7b 2d c9 45 30 8e 13 cf 4a 90 7f d9 63 32 22 58 83 c5 12 c5 a7 f3 42 92 50 2d 49 3a 33 17 2a 6e dd 75 af 66 cc 67 d6 b2 69 25 8a 10 cb 47 90 5e e4 4b 71 14 8e f6 51 b0 a4 99 70 9c 59 ae 09 d9 21 95 83 10 f0 a8 24 c1 59 a5 65 58 2a f9 21 53 aa 83 c6 71 f6 89 f0 20 3d d7 dc b0 b4 ec ce 84 c5 08 32 09 30 be f6 20 1c 76 2e 6b 90 08 48 5a 09 57 e3 5f 0d b6 09 bd b7 3c de 4b 0b a4 b0 11 0c 2a 43 00 88 08 5e d1 77 49 71 48 86 18 ad 2e 46 58 92 c0 19 aa cc 4b dc 84 14 62 42 1a ac 16 81 c0 f4 1a 77 3b 11 b1 12 3d 46 4a 77 7c 2a a7 f7 20 c2 fc 75 b0 24 40 67 b6 ec 3b 79 f1 70 3c 2a 1a ee 71 99 af e4 b2 93 81 40 b9 56 36 37 85 75 58 72 8d 29 4c 9f b3 56 72 43 b6 97 38 62 06 d8 41 8b 36 93 b3 5d 96 0f 1a 12 ad 3c 3b 46 b8 5a 6c aa 86 57 71 42 14 4f b1 bb a2 e8 a2 00 51 b4 02 aa 7f 03 2c b9 61 00 71 60 91 41 11 08 97 fd 2c ab 58 1b a2 60 6c 0d 84 23 79 01 27 9f 7b 15 13 e6 97 59 84 bc 96 41 79 91 7d d6 07 90 95 0c 94 45 66 a9 f5 9b 7c d5 3e 64 9c b0 7c a5 1f 86 a7 5e b4 21 3a 39 34 47 b7 1a 5e cc cc 41 ce 36 04 ad 7a 2c 32 eb 18 78 4c a2 9f 67 31 d9 10 92 00 17 71 ec 1a 2c be d0 14 a6 63 04 5f 87 3f 39 b3 0a c2 63 59 b0 34 bf 81 6a 0d 68 43 a0 2e 30 c7 19 62 13 bb ea 09 28 5c c6 5a c0 bf 6d 0c 29 a8 60 aa 2a 9c 6d 84 4a 0a d1 c7 7b c3 16 8d b2 11 37 d0 1b 29 72 38 45 da f4 5e c8 51 b6 46 9b ab ad 28 7f a4 75 a1 98 4b ce 08 7a 90 ba 76 6d 09 49 a5 bf 21 19 ae e2 02 52 36 1f 63 ab 16 2e 2c a3 51 b8 92 66 da 3a 62 54 bb 15 bf 9e c5 92 e1 a4 1c ad 94 21 76 3b af d7 1a 83 c8 47 97 47 72 0e ec 58 1c 1e dc f6 5c 50 59 72 5e 7d 7d ac 37 9f 15 3a 2d e0 51 85 22 69 86 1c e0 4b c4 55 17 09 00 1d 00 20 dc c3 5a 85 ff e0 f3 1f 1f fa bb c7 0a 51 62 9c c0 03 81 94 4e c2 5c f0 1c 50 92 8e 96 4c 1f 6e
INFO:snap7.connection:Disconnected from 172.25.250.129:102
DEBUG:s7.client:S7CommPlus connection failed: Receive error: [WinError 10054] An existing connection was forcibly closed by the remote host
Traceback (most recent call last):
  File "<frozen runpy>", line 203, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "X\s7_comm\__main__.py", line 9, in <module>
    client.connect(
    ~~~~~~~~~~~~~~^
        "172.25.250.129",
        ^^^^^^^^^^^^^^^^^
    ...<4 lines>...
        protocol=Protocol.S7COMMPLUS,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "X\.venv\Lib\site-packages\s7\client.py", line 124, in connect
    raise RuntimeError(
        f"S7CommPlus connection to {address}:{tcp_port} failed and protocol=S7COMMPLUS was explicitly requested"
    )
RuntimeError: S7CommPlus connection to 172.25.250.129:102 failed and protocol=S7COMMPLUS was explicitly requested

in the meanwhile, you can also reach me directly via Teams https://teams.microsoft.com/l/chat/0/0?users=Erik.Tesar@mhc-solutions.de so we can further diagnose the problem.

The PLC is up to date with a TIA V21 Project and Firmware V4.1.2

[Erik1000]

Also note it triggers the warning from
#761 #710

WARNING:s7.connection:PLC did not provide a scalar ServerSessionVersion attribute. This is the V1-initial S7-1200 firmware band (FW < 4.5 predating TLS) which sends a Struct(314) value and requires the proprietary SessionKey handshake — not yet implemented in python-snap7 (tracked in issue #710). Falling back to legacy PUT/GET: db_read/db_write will work, browse() will not.