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Redundant Failsafe Internet Gateway

An Internet Gateway with VPN for a company with several international subsidiaries.


The customer is an Austrian company with several subsidiaries around the globe. This solution implements basic Internet gateway and Intranet functionality, including firewall and VPN, mail server with virus check and IMAP service, internet proxy, time and name server, intranet web server with SMB/CFS access, and an LDAP database with central administration of all permissions.

The standard operational unit consists of four PC's with pair-wise redundant functionality. A similar functional block is deployed in the headquarters and in each subsidiary. The setup is symmetric; administration is possible from any subsidiary, and data is automatically synchronized. This allows administrator-less operation in all subsidiaries.

Each operational unit is autonomous; when one subsidiary loses its internet connections, the rest of the network continues to function normally. Setup and integration of new subsidiaries is comparatively easy.

The installation supercedes an older corporate frame relay, and saves considerable costs while greatly extending the functionality.

A tight firewall, coupled with the use of proxy servers, creates a double security barrier. Virus scanners and continuous monitoring protect the inner corporate network.

Design Requirements

Central administration
All administration is done from the headquarters. No qualified personnal is required in the subsidiaries. All permissions can be adjusted in a central place.
Autonomous operation
When a subsidiary, or the headquarters, experience a loss of power or internet connection, the system will continue to function in the other subsidiaries. All required data is kept local in each subsidiary.
Easy replacement process
Replacement of defective hardware can be done from headquarters. The process is: When the box is hooked up in the subsidiary, it will automatically synchronize with the other server or firewall. There is no time pressure since the system continues operation with only one server/firewall.
Low cost components
All software components except the virus scanner engine are standard free software and can be duplicated without cost. All hardware components are standard PC's.
Low bandwidth usage
Data synchronization is done with bandwidth saving protocols.


The internet gateway is designed as a functional block of four standard PC's. Two of them act as firewalls, two as servers. Both firewall and server come in redundant pairs; should one of them experience a hardware failure, the other one takes over service automatically.

The firewall PC is a multi-line VPN endpoint. It operates dedicated VPN connections to all firewalls of all other subsidiaries. Both firewalls may be hooked up to different Internet providers for redundancy. Firewalls automatically detect dead VPN connections and change the routing accordingly.

The firewall PC also acts as a firewall with NAT (Network Address Translation) for the servers in the block. Firewall logs are sent to the servers for evaluation.

The server PC implements all networking related services, i.e. a secure mail server with virus scanning and IMAP service, an Internet proxy server for HTTP and FTP, time and name services (NTP and DNS), an intranet web server with group-specific protected areas, and an LDAP server.

The intranet service includes a web based administration front-end to administrate users and adjust their access permissions for various services and areas. It also offers a webmail interface to users who prefer that.

All data is automatically synchronized between the servers in a subsidiary and across subsidiaries.

Architectural Overview

Architectural Overview