Proxied versus Filtered

Posted on 2005-04-06
Last Modified: 2010-04-10
I would like to know the difference between proxied services and filtered services, or proxied connections and filtered connections.

Question by:Chuckbuchan

    Author Comment

    if you would also an explanation about dynamic NAT
    LVL 4

    Accepted Solution

    A Proxy works on OSI Layer 7, that means the traffic is interpreted as e.g. eMail, FTP or whatever. So you can create rules based on the corresponding application (e.g. only mails from sender xxx).

    When filtering traffic you work on lower layers (IP in most cases). That means you don't (really) know whether it's an eMail or something else when passing by. You can create rules for source ip address, destination ip address, and some more TCP/IP parameters.


    Author Comment

    do you mean :
    we use proxy services to open ports for applications ,example port 80 [http], port 21[ftp], etc...
    we use packet filtering to allow/deny networks and hosts to get in/out.

    is that what you meant?
    LVL 4

    Expert Comment


    No, udp/tcp ports are part of the ip header. So, you can "filter" them on network layer.

    With proxies you can check for the parameters on APPLICATION level, e.g eMails containing "Viagra", Web-Access to ".ru"-domains or to websites containing java-scripts.


    Author Comment

    on your comment above it sounds like web blockers they use proxies , because you can block any website  related to a certain topic. like you said eMails containing "Viagra", Web-Access to ".ru"-domains or to websites containing java-scripts.

    I was just wondering if this is the case, why would they have both options on the fire box [ Proxied services and web blocker] since both they have the same functionnality. I don't know If I am correct though.

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