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How to configure a firewall to communicate with an upstream router

My client is using the same vendor for his routers and switches, but is now trying to incorporate a new firewall product from a different vendor. We are having configuration problems, and the firewall is not communicating with the upstream router. When this occurs, what are the most common causes?

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There's no reason that you should have to purchase your firewalls and other networking equipment from the same vendor. In fact, I've never done this in any of the enterprises where I've worked or consulted in the past. Your firewall should be able to interoperate with any network infrastructure that you put in place. That's the whole point behind using standards such as TCP/IP for network communications.

I suspect that you're experiencing one of many simple networking problems. It could be that the switch/router port that your firewall is connected to is incorrectly configured. Perhaps the network interface in the firewall is defective. Are you certain that you've applied an appropriate IP address to the firewall's interface?

My recommendation is to approach this problem in the same manner as you'd handle any device that you're not able to connect to your network. Check the simple things first (link lights, IP configuration, etc.) and then expand outward to more advanced techniques, such as sniffing the network segment using a tool like Wireshark.

More information:

  • A reader asks Mike Chapple, "Will there be DMZ routing issues if several firewalls serve as the default gateway?"
  • Get the latest news and expert advice on network firewalls.
  • This was first published in January 2009

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