Difference between Proxy Server and Firewall

Just an addition to the above, very good, explanation. Proxy servers also can be setup as a cache for web content. So if you have been surfing a website allo those pages you visited are stored in the proxy server's cache. Now if someone else or also you, visit that site at a later time again, the proxy server just downloads the the changes from the original site and serves the rest of the contents to you directly from it's own cache. This makes access for you much faster and it also releases some of the load from the internet connection.

Just my £2.00 worth

Proxy server protects the clients internal IP address from being 'seen' on the internet as all traffic leaves with the ip address assigned to the proxy server. Proxy servers also often hold caches of the web sites that users have visited recently to speed up the process of getting regularly called pages. Proxies generally work at layer 7

Reverse proxy is exactly the same but is normally used for inbound. For example, if you host a web site that is available to the internet community, the web browser url that put in will get them to the external router/firewall and then 'firewall rules' are used to forward that traffic to the internal web server.  

A firewall opertates ay layer 3. Its function is to interrogate traffic that passes through its interfaces and compare each packet against its 'rules'. If the traffic is allowed the taffic is accepted and passed out of the relevant interface the other side. If the traffic is not allowed it will either be dropped or rejected. Firewalls can also use stateful paket inspection (SPI). This is a process where the firewall will establish a connection with a calling/sending device and create a session state for that communication. In this entry it keeps details of the tcp packet number for example so if some more traffic arrives from that location the firewall can see that a communication was expected, the tcp packet numbers are the ones it anticipated and accepts the traffic etc.

Some devices are either a proxy server or a firewall whilst others can be both.
For example, MS ISA server can be installed as simply a caching proxy server or as both a Proxy and a firewall through the setup program.

Regards

Keith

- 1)=If you disable the firewall (only the router works) all LAN station have direct and full Internet access.
You can imagine the firewall as a set of restrictive rules (all is enabled when these rules are inactive). So you can eliminate/change some rules to create a hole (range) of port by example.
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- 1) = If you disable proxy there is no way to connect from the LAN to the Internet servers

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2==Services which use low-level TCP/IP protocols (ping, traceroute,..) will work behind firewall (if they are not disabled by firewall restrictions).

2==Services which use low-level TCP/IP protocols (ping, traceroute,..) will not work behind proxy.
 
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3---Firewall works on the packet level. It can apply rules on packets (by checking the source/destination IP address, source/destination port,...) to decide whether the packet will be forwarded or denied.
Proxy works on application protocol level. They doesn't work on packet level so they can't forward packets.
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