100 lines
3.9 KiB
Plaintext
100 lines
3.9 KiB
Plaintext
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#!/sbin/ipf -f -
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#
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# SAMPLE: RESTRICTIVE FILTER RULES
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#
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# THIS EXAMPLE IS WRITTEN FOR IP FILTER 3.3
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#
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# ppp0 - (external) PPP connection to ISP, address a.b.c.d/32
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#
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# ed0 - (internal) network interface, address w.x.y.z/32
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#
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# This file contains the basic rules needed to construct a firewall for the
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# above situation.
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#
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#-------------------------------------------------------
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# *Nasty* packets we don't want to allow near us at all!
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# short packets which are packets fragmented too short to be real.
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block in log quick all with short
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#-------------------------------------------------------
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# Group setup.
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# ============
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# By default, block and log everything. This maybe too much logging
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# (especially for ed0) and needs to be further refined.
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#
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block in log on ppp0 all head 100
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block in log proto tcp all flags S/SA head 101 group 100
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block out log on ppp0 all head 150
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block in log on ed0 from w.x.y.z/24 to any head 200
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block in log proto tcp all flags S/SA head 201 group 200
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block in log proto udp all head 202 group 200
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block out log on ed0 all head 250
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#-------------------------------------------------------
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# Localhost packets.
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# ==================
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# packets going in/out of network interfaces that aren't on the loopback
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# interface should *NOT* exist.
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block in log quick from 127.0.0.0/8 to any group 100
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block in log quick from any to 127.0.0.0/8 group 100
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block in log quick from 127.0.0.0/8 to any group 200
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block in log quick from any to 127.0.0.0/8 group 200
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# And of course, make sure the loopback allows packets to traverse it.
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pass in quick on lo0 all
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pass out quick on lo0 all
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#-------------------------------------------------------
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# Invalid Internet packets.
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# =========================
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#
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# Deny reserved addresses.
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#
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block in log quick from 10.0.0.0/8 to any group 100
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block in log quick from 192.168.0.0/16 to any group 100
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block in log quick from 172.16.0.0/12 to any group 100
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#
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# Prevent IP spoofing.
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#
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block in log quick from a.b.c.d/24 to any group 100
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#
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#-------------------------------------------------------
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# Allow outgoing DNS requests (no named on firewall)
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#
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pass in quick proto udp from any to any port = 53 keep state group 202
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#
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# If we were running named on the firewall and all internal hosts talked to
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# it, we'd use the following:
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#
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#pass in quick proto udp from any to w.x.y.z/32 port = 53 keep state group 202
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#pass out quick on ppp0 proto udp from a.b.c.d/32 to any port = 53 keep state
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#
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# Allow outgoing FTP from any internal host to any external FTP server.
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#
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pass in quick proto tcp from any to any port = ftp keep state group 201
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pass in quick proto tcp from any to any port = ftp-data keep state group 201
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pass in quick proto tcp from any port = ftp-data to any port > 1023 keep state group 101
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#
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# Allow NTP from any internal host to any external NTP server.
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#
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pass in quick proto udp from any to any port = ntp keep state group 202
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#
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# Allow outgoing connections: SSH, TELNET, WWW
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#
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pass in quick proto tcp from any to any port = 22 keep state group 201
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pass in quick proto tcp from any to any port = telnet keep state group 201
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pass in quick proto tcp from any to any port = www keep state group 201
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#
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#-------------------------------------------------------
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block in log proto tcp from any to a.b.c.d/32 flags S/SA head 110 group 100
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#
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# Allow incoming to the external firewall interface: mail, WWW, DNS
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#
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pass in log quick proto tcp from any to any port = smtp keep state group 110
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pass in log quick proto tcp from any to any port = www keep state group 110
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pass in log quick proto tcp from any to any port = 53 keep state group 110
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pass in log quick proto udp from any to any port = 53 keep state group 100
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#-------------------------------------------------------
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# Log these:
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# ==========
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# * return RST packets for invalid SYN packets to help the other end close
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block return-rst in log proto tcp from any to any flags S/SA group 100
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# * return ICMP error packets for invalid UDP packets
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block return-icmp(net-unr) in proto udp all group 100
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