Kamatchi Sundaram wrote:
> Hi,
>
> I have some set of doubts in Firewall Implementation.
>
> 1) What it's meant by IN filter and Out filter?
>
An IN filter, filters packets when they first reach the Firewall, usually before the
kernel sees the packet. An OUT filter, filters packets as they leave the Firewall,
after going through the kernel and routing mechanisms.
>
> , 2) Where exactly the firewall come into picture, when filtering the packets? (Is
>it correct that, for incoming packets the filtering will be done before the
>forwarding decision is taken and for outgoing packet the decision will be taken after
>the forwarding . If it's correct, please give the detail about the implementation.)
>
See #1
>
> 3) Some firewall products supports to configure like : rule1 on circuit 2 reject in
>(incoming traffic) (if) rule2 & filter1 & filter2 (true).
>
> What exactly the above statement means. ( is the symbol "&" means if the packet
>satisfies all the three (i.e. filter1 and filter2 and rule2), or any rule, be allowed
>or rejected.
> ------ I want clear explanation for this.
>
The '&' symbol represents an 'AND' operation. All criteria must be tru, for an 'AND'
statement to be true.
>
> 4) Can i say, a set of rules combined to form a filter? ( The absolute meaning of
>the filter.)
>
> 5) What are the basic criterias to form a set of filters. ( Is it based on the
>services or protocols or interfaces etc.)
>
Yes.
>
> thanks in advance,
> G.kamatchi soundaram,
> Software engineer,
> Future software,
> 480, Mount road,
> Nandanam,
> chennai -- 600 017.
Jack Dingler
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