Passthrough Mode

Passthrough Mode allows your CTM unit to forward the IP address assigned by your cellular carrier directly to a device connected through its Ethernet port. This enables the connected device—such as a router, PC, or industrial controller—to appear directly on the cellular network, rather than sitting behind the CTM’s local Network Address Translation (NAT).

Typical Applications

Passthrough Mode is useful in scenarios such as:

• Establishing IPSec VPN tunnels

• Providing cellular network access to a router or firewall

• Supporting network failover

• Enabling industrial controllers to host services on various or dynamic ports

Modes of Operation

Pass-Through Auto

In Auto mode, the CTM automatically passes the following carrier-assigned parameters to the connected device via DHCP:

• IP address

• Gateway IP

• Subnet mask

• DNS

The connected device must be configured as a DHCP client.

Configuration Requirements

• Ethernet0 must be set to pass-through-auto mode.

• Packet forwarding must be enabled.

• NAT (masquerading) must be disabled on the firewall WAN zone.

Pass-Through Static

In Static mode, network parameters are manually configured:

1. IP address: Must match the IP provided by the carrier.

2. Gateway IP: A LAN network IP within the same subnet (can be chosen arbitrarily).

3. Subnet mask: Must cover the carrier-provided IP range.

The connected device can be:

1. Assigned the carrier-provided IP manually, or

2. Assigned the IP via the CTM’s DHCP server.

Additional Notes:

1. The LAN network must include the carrier IP address within its subnet.

2. Mobile-to-mobile connectivity to the network’s gateway IP is possible by selecting an alternate gateway IP.

Configuration Requirements

1. Ethernet0 must be set to pass-through-static mode.

2. Network gateway IP = Ethernet0 IP.

3. Network subnet = Ethernet0 subnet.

4. DHCP server may be enabled or disabled.

5. Packet forwarding must be enabled.

6. NAT (masquerading) must be disabled on the firewall WAN zone.

Example

Cellular network provided network parameters:

Network parameters passed to the connected device:

CTM Configuration

• network → wired → eth0 interface

  • Network settings

    • Mode of operation: Pass through mode static IP

    • Protocol: Use static IP Address

    • IP Address: 10.11.12.1

    • Netmask: /24

  • DHCP server

    • If enabled

      • DHCP range start IP address and DHCP range end IP address: 10.11.12.13

    • Or it can be disabled.

• network → firewall → general

  • Packet forwarding: Enabled

  • Zones → wan → Enable NAT: Unchecked

When to Use Each Mode

Use Auto Mode when:

• Carrier-provided IPs are dynamic or unknown.

• The connected device is set to use DHCP.

• You want a plug-and-play setup with minimal configuration.

• The connected device needs direct public internet access (e.g., router, firewall, industrial controller).

Use Static Mode when:

• Carrier-provided IP subnet is static (IP may still be dynamic).

• Greater control over network settings is required.

• Your network design or security policies require static addressing.

• You want to assign a specific IP via the CTM’s DHCP server, or configure IP settings manually.

• The carrier-provided gateway IP interferes with mobile-to-mobile communication.