A firewall is a security appliance that blocks unauthorized access to your network while leaving authorized traffic flowing. An IDS system, on the other hand, is a security system that monitors network traffic for signs of malicious activity.
A firewall is typically used to protect a single network from unauthorized access. An IDS system, on the other hand, can be used to protect a network from a variety of threats, including unauthorized access, spyware, and malware.
Firewalls are typically less expensive than IDS systems, and they can be configured to block more types of traffic. IDS systems, on the other hand, can be more accurate in identifying malicious activity, and they can be used to monitor multiple networks.
