Compare an intrusion system with a firewall.

What will be an ideal response?

Although similar in nature to a firewall, an intrusion system differs in that a firewall limits access from external networks by silently filtering packets based on such criteria as the sender's IP address or whether the packet was requested by a device on the protected network. Firewalls do not alert security personnel that a malicious packet has been destroyed. An intrusion system, on the other hand,watches for systematic attacks (instead of just a single malicious packet) and then takes specified action. Intrusion systems can also watch for any attacks that may originate from inside the network as well.