40 lines
1.5 KiB
Plaintext
40 lines
1.5 KiB
Plaintext
Configuring IP Filter for firewall usage.
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=========================================
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Step 1 - Block out "bad" IP packets.
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------------------------------------
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Run the perl script "mkfilters". This will generate a list of blocking
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rules which:
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a) blocks all packets which might belong to an IP Spoofing attack;
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b) blocks all packets with IP options;
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c) blocks all packets which have a length which is too short for
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any legal packet;
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Step 2 - Convert Network Security Policy to filter rules.
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---------------------------------------------------------
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Draw up a list of which services you want to allow users to use on the
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Internet (e.g. WWW, ftp, etc). Draw up a separate list for what you
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want each host that is part of your firewall to be allowed to do, including
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communication with internal hosts.
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Step 3 - Create TCP "keep state" rules.
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---------------------------------------
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For each service that uses TCP, create a rule as follows:
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pass in on <int-a> proto tcp from <int-net> to any port <ext-service> flags S/SA keep state
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where
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* "int-a" is the internal interface of the firewall. That is, it is the
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closest to your internal network in terms of network hops.
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* "int-net" is the internal network IP# subnet address range. This might
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be something like 10.1.0.0/16, or 128.33.1.0/24
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* "ext-service" is the service to which you wish to connect or if it doesn't
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have a proper name, a number can be used. The translation of "ext-service"
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as a name to a number is controlled with the /etc/services file.
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