#!/bin/sh################ Start of IPFW rules file ####################### Flush out the list before we begin.ipfw -q -f flush# Set rules command prefixcmd="ipfw -q add"skip="skipto 800"pif="rl0"     # public interface name of NIC              # facing the public Internet################################################################## No restrictions on Inside LAN Interface for private network# Change xl0 to your LAN NIC interface name#################################################################$cmd 005 allow all from any to any via xl0################################################################## No restrictions on Loopback Interface#################################################################$cmd 010 allow all from any to any via lo0################################################################## check if packet is inbound and nat address if it is#################################################################$cmd 014 divert natd ip from any to any in via $pif################################################################## Allow the packet through if it has previous been added to the# the "dynamic" rules table by a allow keep-state statement.#################################################################$cmd 015 check-state################################################################## Interface facing Public Internet (Outbound Section)# Check session start requests originating from behind the# firewall on the private network or from this gateway server# destined for the public Internet.################################################################## Allow out access to my ISP's Domain name server.# x.x.x.x must be the IP address of your ISP's DNS# Dup these lines if your ISP has more than one DNS server# Get the IP addresses from /etc/resolv.conf file$cmd 020 $skip tcp from any to x.x.x.x 53 out via $pif setup keep-state# Allow out access to my ISP's DHCP server for cable/DSL configurations.$cmd 030 $skip udp from any to x.x.x.x 67 out via $pif keep-state# Allow out non-secure standard www function$cmd 040 $skip tcp from any to any 80 out via $pif setup keep-state# Allow out secure www function https over TLS SSL$cmd 050 $skip tcp from any to any 443 out via $pif setup keep-state# Allow out send & get email function$cmd 060 $skip tcp from any to any 25 out via $pif setup keep-state$cmd 061 $skip tcp from any to any 110 out via $pif setup keep-state# Allow out FreeBSD (make install & CVSUP) functions# Basically give user root "GOD" privileges.$cmd 070 $skip tcp from me to any out via $pif setup keep-state uid root# Allow out ping$cmd 080 $skip icmp from any to any out via $pif keep-state# Allow out Time$cmd 090 $skip tcp from any to any 37 out via $pif setup keep-state# Allow out nntp news (i.e. news groups)$cmd 100 $skip tcp from any to any 119 out via $pif setup keep-state# Allow out secure FTP, Telnet, and SCP# This function is using SSH (secure shell)$cmd 110 $skip tcp from any to any 22 out via $pif setup keep-state# Allow out whois$cmd 120 $skip tcp from any to any 43 out via $pif setup keep-state# Allow ntp time server$cmd 130 $skip udp from any to any 123 out via $pif keep-state################################################################## Interface facing Public Internet (Inbound Section)# Check packets originating from the public Internet# destined for this gateway server or the private network.################################################################## Deny all inbound traffic from non-routable reserved address spaces#$cmd 300 deny all from 192.168.0.0/16  to any in via $pif  #RFC 1918 private IP$cmd 301 deny all from 172.16.0.0/12   to any in via $pif  #RFC 1918 private IP$cmd 302 deny all from 10.0.0.0/8      to any in via $pif  #RFC 1918 private IP$cmd 303 deny all from 127.0.0.0/8     to any in via $pif  #loopback$cmd 304 deny all from 0.0.0.0/8       to any in via $pif  #loopback$cmd 305 deny all from 169.254.0.0/16  to any in via $pif  #DHCP auto-config$cmd 306 deny all from 192.0.2.0/24    to any in via $pif  #reserved for docs$cmd 307 deny all from 204.152.64.0/23 to any in via $pif  #Sun cluster$cmd 308 deny all from 224.0.0.0/3     to any in via $pif  #Class D & E multicast# Deny ident$cmd 315 deny tcp from any to any 113 in via $pif# Deny all Netbios service. 137=name, 138=datagram, 139=session# Netbios is MS/Windows sharing services.# Block MS/Windows hosts2 name server requests 81$cmd 320 deny tcp from any to any 137 in via $pif$cmd 321 deny tcp from any to any 138 in via $pif$cmd 322 deny tcp from any to any 139 in via $pif$cmd 323 deny tcp from any to any 81  in via $pif# Deny any late arriving packets$cmd 330 deny all from any to any frag in via $pif# Deny ACK packets that did not match the dynamic rule table$cmd 332 deny tcp from any to any established in via $pif# Allow traffic in from ISP's DHCP server. This rule must contain# the IP address of your ISP's DHCP server as it's the only# authorized source to send this packet type.# Only necessary for cable or DSL configurations.# This rule is not needed for 'user ppp' type connection to# the public Internet. This is the same IP address you captured# and used in the outbound section.$cmd 360 allow udp from x.x.x.x to any 68 in via $pif keep-state# Allow in standard www function because I have Apache server$cmd 370 allow tcp from any to me 80 in via $pif setup limit src-addr 2# Allow in secure FTP, Telnet, and SCP from public Internet$cmd 380 allow tcp from any to me 22 in via $pif setup limit src-addr 2# Allow in non-secure Telnet session from public Internet# labeled non-secure because ID & PW are passed over public# Internet as clear text.# Delete this sample group if you do not have telnet server enabled.$cmd 390 allow tcp from any to me 23 in via $pif setup limit src-addr 2# Reject & Log all unauthorized incoming connections from the public Internet$cmd 400 deny log all from any to any in via $pif# Reject & Log all unauthorized out going connections to the public Internet$cmd 450 deny log all from any to any out via $pif# This is skipto location for outbound stateful rules$cmd 800 divert natd ip from any to any out via $pif$cmd 801 allow ip from any to any# Everything else is denied by default# deny and log all packets that fell through to see what they are$cmd 999 deny log all from any to any################ End of IPFW rules file ###############################  

備注：參數說明：
#$cmd 300 deny all from 192.168.0.0/16  to any in via $pif  #RFC 1918 private IP
我的IP地址是192.168.21.173，是屬于192.168.0.0/16 IP段，所以這里要注釋掉這一行，允許連接外網，否則主機無法聯網。
$cmd 380 allow tcp from any to me 22 in via $pif setup limit src-addr 2
是開啟SSH默認端口22
3、重啟網絡服務，使防火墻規則生效

/etc/netstart  #重啟網絡
/etc/rc.d/ipfw start     #開啟防火墻
ipfw disable firewall    #關閉防火墻
ipfw enable firewall   #開啟防火墻
/etc/rc.d/ipfw  restart   #重啟防火墻
sh /etc/ipfw.rules     #使防火墻規則生效
4、開啟SSH服務
（1）ee  /etc/inetd.conf  #編輯，去掉sshd前面的#
ssh     stream  tcp     nowait  root    /usr/sbin/sshd          sshd -i -4
（2）ee  /etc/rc.conf   #編輯，在最后添加
sshd_enable="yes"  
（3）ee  /etc/ssh/sshd_config  #編輯配置文件
PermitRootLogin yes   #允許root登錄
PasswordAuthentication yes    #使用密碼驗證
PermitEmptyPasswords no   #不允許空密碼登錄
/etc/rc.d/sshd start  #啟動ssh服務
/etc/rc.d/sshd restart    #重啟ssh
配置完成，現在已經可以使用Putty等遠程連接工具連接服務器了。
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擴展閱讀：
有兩種加載自定義 ipfw 防火墻規則的方法。
其一是將變量 firewall_type 設為包含不帶 ipfw(8) 命令行選項的 防火墻規則 文件的完整路徑。
例如：
add allow in
add allow out
firewall_type="open"參數說明
open ── 允許所有流量通過。
client ── 只保護本機。
simple ── 保護整個網絡。
closed ── 完全禁止除回環設備之外的全部 IP 流量。
UNKNOWN ── 禁止加載防火墻規則。
filename ── 到防火墻規則文件的絕對路徑。
IPFW防火墻規則集樣例在這兩個文件中
/etc/rc.firewall
/etc/rc.firewall6
除此之外， 也可以將 firewall_script 變量設為包含 ipfw 命令的可執行腳本， 這樣這個腳本會在啟動時自動執行。
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