What is the primary difference between the way routers treat packets and the way application proxies handle packets?

Answer 1

A application proxy disassembles each packet as it enters the network. The broken down packet is then examined too see if it meets the criteria set, then the proxy rewrites it, and sends it on its way. The proxy usually will terminate the connection from the source and initiates a new connection from the proxy back to the destination. This can offer greater protection to the machines hosting the applications because there is no direct interaction between the source and the destination.

Plausibly the most commonly used firewall is the router. The router examines the source and destination addresses, as well as the ports. The router uses this data too determine if the packet meets the designated rules to pass through to its intended destination. Keep in mind, there are several different types of routers (aka gateways). Some are simple, only filtering packets by port. Some others filter by IP address and port. The more advanced routers will perform various checks on the credibility of an IP address, thus providing additional protection.