Connections and Network Setup

Important

Connecting an incorrectly configured device to a data transmission network can disrupt communication between other devices. Ensure all connected devices have compatible settings. Network connections involving more than 2 devices should be performed by qualified network personnel.

Quick Start

For a streamlined connection guide, see the Quick Start Guide.

IP Addressing

The Overvis MC251 uses standard TCP/IPv4 addressing for Ethernet communication. DHCP is enabled by default, allowing the device to automatically obtain network settings from your router. Without DHCP the factory default IP address is 192.168.0.111.

IP Addressing Fundamentals

When devices communicate over an Ethernet network using the TCP/IPv4 protocol, each device uses IP addressing settings to identify the sender and receiver of data. MC251 stores the following in its memory:

• IP Address: A unique address within the subnet (four bytes written as integers 0-255, separated by dots)
• Subnet Mask: Identical for all devices within the subnet (written similar to IP address)
• Gateway Address: Used to communicate with other networks

Requirements for Proper Communication:

Devices within a subnet communicate properly when these conditions are met:

• Common Subnet Mask: All devices in the subnet must use the same mask. Most small LANs use 255.255.255.0.
• Valid Mask Format: The mask starts with consecutive 1 bits, followed by consecutive 0 bits.
• Subnet Address: All IP address bits corresponding to the mask’s 1 bits must be identical across all devices. Common LANs use 192.168 as the address prefix with mask 255.255.255.0. The third byte can serve as a subnet number in complex LANs; in smaller LANs, it’s typically 0.
• Unique Host Address: The IP address bits corresponding to the mask’s 0 bits must be unique to each device within the subnet.
• Gateway Configuration: A router or gateway device that communicates with other networks typically uses an address like 192.168.0.1, 192.168.0.100, or 192.168.0.101. Other devices can use this address as their gateway. The gateway address is not required for intra-subnet communication—only for connecting to external networks (such as the Internet).

Table 1 - Factory addressing settings for MC251

Parameter	Value
Addressing using DHCP	Yes
IP Address	192.168.0.111
Subnet Mask	255.255.255.0
Gateway	192.168.0.1

Ethernet Connection Methods

With factory default settings, MC251 supports two connection methods via Ethernet.

Method 1: Network with DHCP Server

If your network includes a router or DHCP server that assigns IP addresses to new devices:

1. Connect MC251 to the network
2. Wait for the device to obtain an IP address (appears on the display with (E) prefix for Ethernet)
3. If the display shows 0.0.0.0, the address has not been received yet
4. If 192.168.0.111 appears after 20-60 seconds, DHCP acquisition failed and the device switched to its static address

Method 2: Direct Connection or Network Without DHCP

If DHCP is unavailable, or MC251 is connected directly to a computer:

1. MC251 will switch to static addressing after 20-60 seconds
2. Configure the client device with:
   • Subnet mask: 255.255.255.0
   • IP address: 192.168.0.X (where X = 1-254, excluding 111)
   • Ensure the chosen address doesn’t conflict with other devices on the subnet

If your network uses different addressing (different mask or IP range from Table 1), or if 192.168.0.111 is already taken:

1. Temporarily disconnect the conflicting device from the network
2. Establish direct communication between your client device and MC251
3. Configure both devices for proper network communication
4. Reconnect to the network

Configuring Ethernet Connection on Windows PC

In some cases you may need to connect MC251 directly to your computer to access its web interface and change settings. Connect the device with an Ethernet cable to the LAN port on your PC, then configure your network adapter as described below.

The following example shows how to configure a Windows PC (Windows 7/8/10/11) to communicate directly with MC251 using factory settings. For other operating systems, configure your client device’s addressing according to its documentation.

How to access network adapter settings on Windows 7 / 8 / 10

1. Log in as administrator
2. Select Start → Control Panel
3. If items are categorized, select Network and Internet
4. Go to Network and Sharing Center
5. In the left sidebar, select Change adapter settings

How to access network adapter settings on Windows 11

1. Log in as administrator
2. Select Start → Settings
3. Select the Network and Internet category
4. Expand Advanced Network Settings
5. Select More network adapter options

Configuring the Network Adapter

1. In the Connections window, select the desired network adapter. If multiple connections appear, choose the correct one by adapter name or consult your system administrator.

2. Right-click the connection icon and select Properties. The Properties window opens (Fig. 1).

   

   Fig. 1 – Connection properties window in Windows

   

   Fig. 2 – TCP/IPv4 properties window in Windows

3. Select Internet Protocol Version 4 (TCP/IPv4) from the component list. Ensure it’s enabled (checkbox is checked). Click Properties. The TCP/IPv4 properties window opens (Fig. 2).

4. Select Use the following IP address

5. In the IP address field, enter an address in the range 192.168.0.1 to 192.168.0.254 (excluding 192.168.0.111, which MC251 uses)

6. In the Subnet mask field, enter 255.255.255.0

7. Leave Default gateway, Preferred DNS server, and Alternate DNS server fields blank or unchanged

8. Click OK to close the Protocol Settings window

9. Click OK to close the Connection Settings window

10. If prompted to restart the PC, select Yes

Internet Connection via Ethernet

STRONGLY RECOMMENDED

Connect the device to the Internet under the supervision of your LAN system administrator and/or Internet service provider representative.

Basic Internet Setup

To connect MC251 to the Internet via Ethernet:

1. Connect MC251 to a local network router with DHCP addressing enabled
2. Ensure the router is connected to your Internet service provider (ISP)
3. Do not connect MC251 directly to the ISP’s cable

This setup enables outgoing connections (e.g., VPN connection to Overvis cloud server, connections to other servers using hostnames or static IP addresses).

graph LR
    A[MC251] -->|Ethernet| B[Router]
    B -->|WAN| C[Internet/ISP]
    B -->|LAN| D[Local Network]
    C --> E[Overvis Cloud Server / Remote Modbus TCP Devices]
    D --> F[Modbus TCP Devices]

Fig. 3 – MC251 Internet connection topology via Ethernet with DHCP

Incoming Connections Setup

To access the device from the Internet via incoming connections (direct TCP connection or web interface):

1. Acquire a Static IP: Get a dedicated line with a static IP address from your ISP

   • Connect the ISP cable to the router’s uplink port (usually color-coded, see router documentation)
   • Use a straight-through Ethernet cable to connect MC251 to the router

2. Configure Router: Following your ISP’s recommendations, configure the router for Internet access using the router documentation.

3. Set Up Port Forwarding: Configure the router to redirect queries from your static public IP address to MC251’s local IP address (factory default: 192.168.0.111)

   • For web interface access: redirect to port 80 on MC251’s local address
   • For Modbus TCP or tunnel access: redirect to the incoming Ethernet connections port (factory default: 502).

   graph LR
       A[Internet Client] -->|Public IP:Port| B[Router]
       B -->|Port Forward| C[MC251]
       C -->|RS-485| D[Modbus Devices]

   Fig. 4 – MC251 incoming connections via port forwarding

4. Configure DHCP Reservation: Either:

   • Configure the router to always assign the same IP address to MC251 via DHCP, OR
   • Disable DHCP in MC251 settings and use a static IP

   This ensures port forwarding works correctly.

5. Verify Security: Confirm that MC251’s Internet connection is protected by standard security measures (see Connection Security)

6. Access the Device: When accessing MC251 from the Internet, use the static IP address provided by your ISP and the port specified in your port forwarding configuration

GSM Connection

STRONGLY RECOMMENDED

If you are using corporate IoT APN, connect the device to the Internet under the supervision of your mobile service operator representative.

Ensure your tariff plan includes GPRS or LTE service (for Internet connectivity) and/or SMS messaging (for SMS-based control).

Basic GSM Setup

To connect MC251 via GSM:

1. Obtain SIM Card: Get a SIM card from your GSM operator
2. Install Hardware: Insert the SIM card into MC251 and connect the appropriate antenna to ensure proper signal strength at the MC251 location
3. Verify SIM Recognition: After starting MC251, confirm the SIM card is correctly identified
   • After communication initialization, the GSM indicator should blink continuously
   • If the indicator remains off for more than 4 seconds, check the SIM card, antenna, and GSM signal level on the MC251 display
4. Verify Internet Connection (if using GPRS/LTE): Ensure the operator settings are correct
   • When connected to the Internet, the GSM indicator flashes 3 times per second
   • If flashing less frequently, check the APN settings
5. Configure APN: If necessary, manually configure the APN according to your operator’s recommendations (see APN Configuration Examples below)

This setup enables outgoing connections (connecting to Overvis cloud server, or to other servers with static IP addresses on the Internet).

graph LR
    A[MC251] -->|GSM/LTE| B[Cellular Network]
    B --> C[Internet]
    C --> D[Overvis Cloud Server / Remote Modbus TCP Devices]
    A -->|RS-485| E[Modbus Devices]

Fig. 5 – MC251 Internet connection topology via GSM/LTE

APN Configuration Examples

Common APN Settings by Operator

United States:

• T-Mobile: fast.t-mobile.com
• AT&T: broadband or phone
• Verizon: vzwinternet

Europe:

• Vodafone (UK): internet or pp.vodafone.co.uk
• O2 (UK): mobile.o2.co.uk
• Orange (France): orange or orange.fr
• Deutsche Telekom (Germany): internet.t-mobile or internet.telekom

Other Regions:

• Contact your GSM operator for specific APN settings
• Some operators require username and password in addition to APN
• M2M/IoT SIM cards may use different APNs than consumer SIM cards

To configure the APN, use the MC251 web interface or modify register 2200-2263 via Modbus. See Modbus Interface for details.

Incoming Connections via GSM

1. Obtain Static IP Service: Get a static IP SIM card or service from your operator
2. Install Hardware: Insert the SIM card and connect the antenna to ensure proper signal strength at the MC251 location
3. Configure Device:
   • Set the incoming GSM connections port in settings.
   • Configure APN settings according to your operator’s recommendations
   • Restart MC251
4. Verify Connection: Confirm the SIM card is identified correctly
   • After interface initialization, the GSM indicator should continue to flash
   • If the indicator remains off for more than 4 seconds, check the SIM card, antenna, and GSM signal level on the device display

Note

Your operator may provide alternative access methods, such as private IP addresses instead of public IP addresses. Private IPs are used to interlink devices within the operator’s network without providing full Internet access.

Connection Security

MC251 provides several security features to protect against unauthorized access:

Built-in Security Features

MC251 has basic protection against unauthorized access via network. Access for writing and/or reading via Modbus or SMS can be deactivated in settings.

Device settings can be changed remotely by entering a password (minimum 5 characters). Access passwords can be set for restriction of writing and/or reading via Modbus or SMS.

When entering the password, all settings are only available to the specific client using the specific protocol. In case of no requests from the client over a long period, the access returns to locked mode.

SECURITY WARNING

For Modbus connections, passwords are transmitted in unencrypted form. Even with correct password authentication, the HTTP and Modbus connections remain unsecured at all segments except VPN and GSM.

Security Limitations and Recommendations:

• Attack Protection: The device protection system is not designed to counter malicious network attacks, especially denial-of-service attacks aimed at blocking MC251 rather than gaining access
• Network Segmentation: For complex and large networks (especially when providing Internet access to MC251), it is strongly recommended to:
  • Separate MC251 from unprotected networks using standard security equipment
  • Use a properly configured router with traffic filtering
  • Deploy a firewall or similar protective measures

Server Connection

MC251 is designed to operate linked to the Overvis Cloud server for configuration, data collection and management.

About Overvis

Overvis (www.overvis.com) is a system for monitoring and remote control of technological processes that enables you to read data from and control devices including MC251, store data in a database, review the data in various formats, and receive alarm notifications via SMS or email.

After the Internet access is established, MC251 would automatically connect to the Cloud Server VPN.

For a newly connected MC251, all you need then is to link it to your Overvis account.

Connection Methods Overview

To link the MC251 to your Overvis account, use the registration information from your MC251 label:

Method 1: Use PIN/QR code from the device label

Method 2: Manually enter and follow the link from the label

Detailed connection procedure is in Quick Start Guide.

sequenceDiagram
    participant MC251
    participant Overvis
    participant User

    MC251->>Overvis: Connect & send handshake (unique key)
    Overvis->>MC251: Send VPN configuration
    MC251->>Overvis: Connect to VPN & send handshake
    Overvis->>MC251: Confirm handshake
    Note over MC251,Overvis: Connection established, waiting for binding

    User->>Overvis: Scan QR code / Enter PIN URL
    User->>Overvis: Login to account
    User->>Overvis: Submit PIN in "Create Network" page
    Overvis->>Overvis: Link PIN to device key address
    Overvis->>Overvis: Find matching connection IP by device key
    Overvis->>User: Create network under user's account

    loop Data Communication
        User->>Overvis: Request device data
        Overvis->>MC251: Read registers (via established VPN connection)
        MC251->>Overvis: Return data
        Overvis->>User: Display data
    end

Fig. 6 – Connection sequence for PIN/QR code method (VPN connection)

Connection Flow: MC251 initiates outbound connection to Overvis VPN and maintains it. User registers by linking the PIN to this existing connection. No port forwarding required.

Prerequisites:

• MC251 connected to Internet (via Ethernet or GSM)
• QR code label on device (or PIN code from label)
• Overvis Cloud account (or create during setup)

Connection Steps:

1. Verify Internet Connection

   Ensure MC251 is connected to the Internet. Check the device display for a valid IP address—the prefix (E) indicates Ethernet connection, (G) indicates GSM. Address should not be 0.0.0.0.

2. Access Overvis Server

   Scan the QR code on the device label with your phone or tablet, OR manually enter the URL from the label (format: https://c.overvis.com/ABCD1234). The link automatically redirects to Overvis server login page with the PIN embedded in the URL.

3. Login or Create Account

   If you have an account, enter your credentials. New users should register for a free account first.

4. Create Network

   After login, Overvis displays the “Create Network” page. If you came from the QR code/link, the PIN is pre-filled automatically. Otherwise, manually enter the PIN from the device label. Click “Check connection” to verify MC251 is online.

5. Configure Network

   Give your network a descriptive name (a “network” represents your MC251 plus all connected Modbus devices). MC251 itself (Modbus unit ID 111) is added automatically. Add your RS-485 devices by selecting models and entering their Modbus addresses.

6. Verify Operation

   Open a device page in Overvis and read parameters to confirm real-time communication.

Connecting to Other Servers

The only method of connection MC251 to other cloud servers and SCADA systems is the direct connection method via Modbus TCP.

Configure MC251 in the monitoring system as a remote Modbus TCP device. This requires setting up port forwarding on your router to redirect external connections to MC251’s local IP address and Modbus TCP port (default: 502). Your server will initiate connections to MC251 through your router, similar to Method 3 described above. You’ll need a static public IP address from your ISP, or alternatively, you can use a secure WireGuard VPN tunnel to bypass the need for public IP exposure.

Since MC251 uses the standard Modbus TCP protocol for direct connections, no special server software is required—any Modbus TCP client can communicate with the device. See the Modbus Interface documentation for complete register mappings and communication protocols.

Troubleshooting

Problem: MC251 display shows 0.0.0.0

The DHCP server is not responding. Wait up to 60 seconds for MC251 to switch to its static IP 192.168.0.111. If the issue persists, verify the network cable is properly connected and check your router’s DHCP settings.

Problem: Cannot access MC251 web interface

Verify your client device is on the same subnet as MC251. Check firewall settings on your client device and confirm the MC251 IP address shown on the display. You can press the R button briefly to grant temporary password-free access.

Problem: LAN LED is off

Check the Ethernet cable connection and verify it’s not damaged. Try using a different cable to rule out cable faults.

Problem: GSM LED stays off

The SIM card may not be inserted correctly—remove and reinsert it. Check that the SIM card PIN is disabled (disable it using a phone before inserting). Verify the antenna is connected properly. Poor signal strength may require relocating MC251 or using an external antenna.

Problem: GSM LED blinks slowly (every 1.5s) but no Internet

This indicates incorrect APN settings. Verify the APN configuration with your operator. Check that your SIM card has an active data plan and review the APN configuration in MC251 settings.

Problem: Cannot receive SMS commands

Verify the SIM card phone number is correct. Check the SMS format according to the Modbus Interface documentation. Ensure SMS service is enabled on the SIM card and verify any SMS passwords are configured correctly.

Problem: SRV LED stays off

MC251 is not connected to the Internet—check your Ethernet or GSM connection. Verify the Cloud server connection is enabled in the web interface. Check that the server address and port are correct in settings. Your network firewall may be blocking outgoing connections.

Problem: “Device already registered” error

The device is bound to another Overvis account. Use the Restart Activation button in the Cloud settings page to unbind it, or contact the previous owner to remove the device from their account.

Problem: Intermittent connection drops

Check that the power supply voltage is within the required range (9-30V DC) and can provide sufficient current (up to 500mA). Look for electrical noise or interference sources near the device. Update MC251 firmware to the latest version.

Problem: RS-485 devices not responding

Verify the RS-485 wiring is correct (A and B terminals). Check that the RS-485 bus termination is properly configured. Verify Modbus RTU/ASCII settings match the connected devices. See the Modbus Interface documentation for detailed communication settings.

Further Reading

• Web Interface — Guide to MC251’s web-based quick setup interface
• Modbus Interface — Register mappings and communication protocols for Modbus TCP/RTU/ASCII

Need Help?

If you’re experiencing issues not covered in this guide, we’re here to help:

• Technical Support: Contact the manufacturer’s support team
• Documentation: Visit overvis.com/support for additional resources
• Community: Check the user forums for solutions from other MC251 users

For warranty service or hardware issues, please contact your authorized distributor or the manufacturer directly. z