次の例に、単一のホスト、サーバー、ルーターに適用するパケットフィルタリング規則を示します。
構成ファイルは、次のような標準的な UNIX 構文規則に従っています。
シャープ記号 (#) は、コメントを含む行を示します。
規則とコメントは、同一の行に共存できます。
規則を読みやすくするために、不要な空白を使用できます。
複数行に渡って規則を記述できます。行の最後のバックスラッシュ (\) は、ルールが次の行に続いていることを示します。
構文についての詳細については、パケットのフィルタリング規則の構成を参照してください。
使用例 5-20 IP フィルタのホスト構成この例は、net0 ネットワークインタフェースを備えるホストシステム上の構成を示しています。
# pass and log everything by default pass in log on net0 all pass out log on net0 all # block, but don't log, incoming packets from other reserved addresses block in quick on net0 from 10.0.0.0/8 to any block in quick on net0 from 172.16.0.0/12 to any # block and log untrusted internal IPs. 0/32 is notation that replaces # address of the machine running IP Filter. block in log quick from 192.168.1.15 to <thishost> block in log quick from 192.168.1.43 to <thishost> # block and log X11 (port 6000) and remote procedure call # and portmapper (port 111) attempts block in log quick on net0 proto tcp from any to net0/32 port = 6000 keep state block in log quick on net0 proto tcp/udp from any to net0/32 port = 111 keep state
このルールセットは、すべてのデータが net0 インタフェースを出入りできる 2 つの制限なしのルールで開始します。2 番目のルールセットは、プライベートアドレス空間 10.0.0.0 および 172.16.0.0 からの受信パケットがファイアウォールの中に入るのをブロックします。次のルールセットは、ホストシステムからの特定の内部アドレスをブロックします。そして、最後の規則セットは、ポート 6000 およびポート 111 から受信されるパケットをブロックします。
使用例 5-21 IP フィルタのサーバー構成この例は、Web サーバーとして機能するホストシステムの構成を示しています。このシステムは net0 ネットワークインタフェースを備えています。
# web server with an net0 interface # block and log everything by default; # then allow specific services # group 100 - inbound rules # group 200 - outbound rules # (0/32) resolves to our IP address) *** FTP proxy *** # block short packets which are packets # fragmented too short to be real. block in log quick all with short # block and log inbound and outbound by default, # group by destination block in log on net0 from any to any head 100 block out log on net0 from any to any head 200 # web rules that get hit most often pass in quick on net0 proto tcp from any \ to net0/32 port = http flags S keep state group 100 pass in quick on net0 proto tcp from any \ to net0/32 port = https flags S keep state group 100 # inbound traffic - ssh, auth pass in quick on net0 proto tcp from any \ to net0/32 port = 22 flags S keep state group 100 pass in log quick on net0 proto tcp from any \ to net0/32 port = 113 flags S keep state group 100 pass in log quick on net0 proto tcp from any port = 113 \ to net0/32 flags S keep state group 100 # outbound traffic - DNS, auth, NTP, ssh, WWW, smtp pass out quick on net0 proto tcp/udp from net0/32 \ to any port = domain flags S keep state group 200 pass in quick on net0 proto udp from any \ port = domain to net0/32 group 100 pass out quick on net0 proto tcp from net0/32 \ to any port = 113 flags S keep state group 200 pass out quick on net0 proto tcp from net0/32 port = 113 \ to any flags S keep state group 200 pass out quick on net0 proto udp from net0/32 to any \ port = ntp group 200 pass in quick on net0 proto udp from any \ port = ntp to net0/32 port = ntp group 100 pass out quick on net0 proto tcp from net0/32 \ to any port = ssh flags S keep state group 200 pass out quick on net0 proto tcp from net0/32 \ to any port = http flags S keep state group 200 pass out quick on net0 proto tcp from net0/32 \ to any port = https flags S keep state group 200 pass out quick on net0 proto tcp from net0/32 \ to any port = smtp flags S keep state group 200 # pass icmp packets in and out pass in quick on net0 proto icmp from any to net0/32 keep state group 100 pass out quick on net0 proto icmp from net0/32 to any keep state group 200 # block and ignore NETBIOS packets block in quick on net0 proto tcp from any \ to any port = 135 flags S keep state group 100 block in quick on net0 proto tcp from any port = 137 \ to any flags S keep state group 100 block in quick on net0 proto udp from any to any port = 137 group 100 block in quick on net0 proto udp from any port = 137 to any group 100 block in quick on net0 proto tcp from any port = 138 \ to any flags S keep state group 100 block in quick on net0 proto udp from any port = 138 to any group 100 block in quick on net0 proto tcp from any port = 139 to any flags S keep state group 100 block in quick on net0 proto udp from any port = 139 to any group 100使用例 5-22 IP フィルタのルーター構成
この例は内部インタフェース net0、および外部インタフェース net1 を備えるルーターの構成を示しています。
# internal interface is net0 at 192.168.1.1 # external interface is net1 IP obtained via DHCP # block all packets and allow specific services *** NAT *** *** POOLS *** # Short packets which are fragmented too short to be real. block in log quick all with short # By default, block and log everything. block in log on net0 all block in log on net1 all block out log on net0 all block out log on net1 all # Packets going in/out of network interfaces that are not on the # loopback interface should not exist. block in log quick on net0 from 127.0.0.0/8 to any block in log quick on net0 from any to 127.0.0.0/8 block in log quick on net1 from 127.0.0.0/8 to any block in log quick on net1 from any to 127.0.0.0/8 # Deny reserved addresses. block in quick on net1 from 10.0.0.0/8 to any block in quick on net1 from 172.16.0.0/12 to any block in log quick on net1 from 192.168.1.0/24 to any block in quick on net1 from 192.168.0.0/16 to any # Allow internal traffic pass in quick on net0 from 192.168.1.0/24 to 192.168.1.0/24 pass out quick on net0 from 192.168.1.0/24 to 192.168.1.0/24 # Allow outgoing DNS requests from our servers on .1, .2, and .3 pass out quick on net1 proto tcp/udp from net1/32 to any port = domain keep state pass in quick on net0 proto tcp/udp from 192.168.1.2 to any port = domain keep state pass in quick on net0 proto tcp/udp from 192.168.1.3 to any port = domain keep state # Allow NTP from any internal hosts to any external NTP server. pass in quick on net0 proto udp from 192.168.1.0/24 to any port = 123 keep state pass out quick on net1 proto udp from any to any port = 123 keep state # Allow incoming mail pass in quick on net1 proto tcp from any to net1/32 port = smtp keep state pass in quick on net1 proto tcp from any to net1/32 port = smtp keep state pass out quick on net1 proto tcp from 192.168.1.0/24 to any port = smtp keep state # Allow outgoing connections: SSH, WWW, NNTP, mail, whois pass in quick on net0 proto tcp from 192.168.1.0/24 to any port = 22 keep state pass out quick on net1 proto tcp from 192.168.1.0/24 to any port = 22 keep state pass in quick on net0 proto tcp from 192.168.1.0/24 to any port = 80 keep state pass out quick on net1 proto tcp from 192.168.1.0/24 to any port = 80 keep state pass in quick on net0 proto tcp from 192.168.1.0/24 to any port = 443 keep state pass out quick on net1 proto tcp from 192.168.1.0/24 to any port = 443 keep state pass in quick on net0 proto tcp from 192.168.1.0/24 to any port = nntp keep state block in quick on net1 proto tcp from any to any port = nntp keep state pass out quick on net1 proto tcp from 192.168.1.0/24 to any port = nntp keep state pass in quick on net0 proto tcp from 192.168.1.0/24 to any port = smtp keep state pass in quick on net0 proto tcp from 192.168.1.0/24 to any port = whois keep state pass out quick on net1 proto tcp from any to any port = whois keep state # Allow ssh from offsite pass in quick on net1 proto tcp from any to net1/32 port = 22 keep state # Allow ping out pass in quick on net0 proto icmp all keep state pass out quick on net1 proto icmp all keep state # allow auth out pass out quick on net1 proto tcp from net1/32 to any port = 113 keep state pass out quick on net1 proto tcp from net1/32 port = 113 to any keep state # return rst for incoming auth block return-rst in quick on net1 proto tcp from any to any port = 113 flags S/SA # log and return reset for any TCP packets with S/SA block return-rst in log on net1 proto tcp from any to any flags S/SA # return ICMP error packets for invalid UDP packets block return-icmp(net-unr) in proto udp all