I have an ISP link that goes into a 5 port fast ethernet switch.
Off of that switch are hanging two firewalls. One with IP (fakes)
Firewall A the other Firewall B
Coming across Firewall B is a VPN that supports connections to SERVER1.
SERVER1's default gateway is set to Firewall B.

When Firewall A is plugged into the switch, traffic to SERVER1 becomes
inordinately slow or stops altogher. When Firewallo A is removed from the
switch, traffic returns to normal.