FreeBSD配置防火墙开启SSH服务的方法

1、配置freebsd 防火墙
ee /etc/rc.conf   #编辑，在最后添加
firewall_enable="yes"  #开启防火墙
net.inet.ip.fw.verbose=1   #启用防火墙日志功能
net.inet.ip.fw.verbose_limit=5  #启用防火墙日志功能
natd_enable="yes"  # 开启防火墙nat功能
natd_interface="rl0"     
natd_flags="-dynamic -m"
firewall_script="/etc/ipfw.rules"      #自定义防火墙规则路径
按esc，回车，再按a保存配置
2、添加防火墙规则

ee /etc/ipfw.rules    #编辑防火墙规则，添加以下代码

#!/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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