The main difference being that firewall performs actions such as blocking and filtering of traffic while an IPS/IDS detects and alert a system administrator or prevent the attack as per configuration.

A firewall allows traffic based on a set of rules configured. It relies on the source, the destination addresses, and the ports. A firewall can deny any traffic that does not meet the specific criteria.

IDS is a passive device which watches packets of data traversing the network, comparing with signature patterns and setting off an alarm on detection on suspicious activity. On the contrary, IPS is an active device working in inline mode and prevent the attacks by blocking it.