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🚀 Update July 2026: New Centro Business 3.0 Firmware "10.04.14" available — fixes the Alcatel/TCL Internet Backup Dongle issue. Details in the Release Note.

IP Passthrough

warning

Expert function​

Swisscom recommends that this function only be configured by experienced IT specialists. Misconfigurations can lead to significant security risks.

Details can be found in the FAQ

IP Passthrough allows all incoming Internet traffic to be forwarded directly to a specific device on the network. The Centro Business receives a public IP address from the Internet and automatically forwards all traffic to the configured client.

Typical use cases​

  • A dedicated hardware firewall (Sophos, FortiGate, pfSense) should receive and manage all incoming Internet traffic
  • A VPN gateway needs to receive all incoming traffic
  • A security appliance should analyse traffic before it reaches the internal network

Configure IP Passthrough​

In the router portal under Network → Passthrough:

  1. Activate IP Passthrough
  2. Connect the device to the dedicated LAN port:
    • Centro Business 2.0: LAN Port 1
    • Centro Business 3.0: LAN Port 5

Configure external gateway/firewall​

Configure the following network settings on the connected device:

ParameterValue
WAN typeEthernet with static IP
IP address172.31.255.6
Subnet mask255.255.255.252
Gateway172.31.255.5
MTU1500

Limitations​

  • Not available with BNS/EC-S contract
  • The Centro Business firewall no longer applies to passthrough traffic
  • Only one device can use IP Passthrough

FAQ - IP Passthrough​

Why does Swisscom declare IP Passthrough as an expert function?

IP Passthrough requires specialised technical knowledge. If downstream devices such as a firewall are not correctly configured, it can lead to attacks on the customer infrastructure. Swisscom recommends using the DMZ function instead to ensure failover protection.

On which Ethernet port is Passthrough activated?
  • Centro Business 2.0: LAN Port 1
  • Centro Business 3.0: LAN Port 5
What is the difference between IP Passthrough and PPP Passthrough?
  • IP Passthrough: The Centro Business establishes the Internet connection and forwards all traffic to the device. Swisscom services (VoIP, TV) remain active on the CB.
  • PPP Passthrough: The connected device establishes the PPPoE connection itself and receives the public IP directly. The Centro Business only acts as a bridge.
What MTU size should be configured?

With IP Passthrough, the standard MTU value of 1500 bytes can be set. This ensures smooth and efficient data transmission.

Are PPP internet connections (with Fixed IP option) regularly interrupted?
n nnYes. Approximately once a week, the PPPoE session is interrupted by the RADIUS server for a few seconds.nn- Time window: approx. every 7–8 days, between 01:00 and 05:00n- Duration: a few seconds (automatic reconnect)nn**Why?**nnSwisscom operates approx. 64,000 PPPoE sessions on 12 ISG servers in Switzerland. Since PPP sessions are static (they remain on the ISG where they initially logged in), an imbalance would occur without periodic disconnects.nnThe so-called "Max-Session-Timer" forces a brief interruption so that:n1. Load balancing: Sessions are evenly distributed across all 12 ISGs, systematically preventing overload on individual servers.n2. Maintenance: Swisscom can cleanly decouple affected sessions when performing maintenance on individual ISG instances (hardware, software, configuration).nn:::tipnThis interruption only affects connections with the "Fixed IP address" option (PPPoE). Standard DHCP connections are not affected.n:::n
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