Next, consider the placement of the firewalls. Are they both directly connected to each other with nothing else in between? If that's the case, consider using a different firewall topology that will get the most out of the two firewalls. For more information on arrangements, read my article Placing systems in a firewall topology. If the firewalls aren't directly connected, make sure that they're not already part of a multi-homed topology implementation.
If there's no business case for redundant firewalls, it might be worthwhile to decommission one of them. Rather than emphasizing performance reasons, I'd cite the hassle and management overhead of maintaining two different systems. Rule changes must be made on both devices separately, effectively doubling administration time. If you're interested in achieving redundancy to protect against a hardware failure, however, consider using two of the same device in a high-availability deployment so that if one firewall fails, the other takes over.
This was first published in July 2007