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1、配置freebsd 防火墙
#!/bin/sh ################ start of ipfw rules file ###################### # flush out the list before we begin. ipfw -q -f flush # set rules command prefix cmd="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 $cmd 999 deny log all from any to any ################ end of ipfw rules file ###############################
备注：参数说明：
#$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，是属于192.168.0.0/16 ip段，所以这里要注释掉这一行，允许连接外网，否则主机无法联网。
$cmd 380 allow tcp from any to me 22 in via $pif setup limit src-addr 2
是开启ssh默认端口22
3、重启网络服务，使防火墙规则生效
/etc/netstart #重启网络
/etc/rc.d/ipfw start #开启防火墙
ipfw disable firewall #关闭防火墙
ipfw enable firewall #开启防火墙
/etc/rc.d/ipfw restart #重启防火墙
sh /etc/ipfw.rules #使防火墙规则生效
4、开启ssh服务
（1）ee /etc/inetd.conf #编辑，去掉sshd前面的#
ssh stream tcp nowait root /usr/sbin/sshd sshd -i -4
（2）ee /etc/rc.conf #编辑，在最后添加
sshd_enable="yes"
（3）ee /etc/ssh/sshd_config #编辑配置文件
permitrootlogin yes #允许root登录
passwordauthentication yes #使用密码验证
permitemptypasswords no #不允许空密码登录
/etc/rc.d/sshd start #启动ssh服务
/etc/rc.d/sshd restart #重启ssh
配置完成，现在已经可以使用putty等远程连接工具连接服务器了。
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扩展阅读：
有两种加载自定义 ipfw 防火墙规则的方法。
其一是将变量 firewall_type 设为包含不带 ipfw(8) 命令行选项的 防火墙规则 文件的完整路径。
例如：
add allow in
add allow out
firewall_type="open"参数说明
open ── 允许所有流量通过。
client ── 只保护本机。
simple ── 保护整个网络。
closed ── 完全禁止除回环设备之外的全部 ip 流量。
unknown ── 禁止加载防火墙规则。
filename ── 到防火墙规则文件的绝对路径。
ipfw防火墙规则集样例在这两个文件中
/etc/rc.firewall
/etc/rc.firewall6
除此之外， 也可以将 firewall_script 变量设为包含 ipfw 命令的可执行脚本， 这样这个脚本会在启动时自动执行。
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