FreeBSD配置防火墻開啟SSH服務的方法是什么
防火墻主要由服務訪問規(guī)則、驗證工具、包過濾和應用網(wǎng)關4個部分組成，防火墻就是一個位于計算機和它所連接的網(wǎng)絡之間的軟件或硬件。這篇文章主要介紹下如何下freebsd下配置防火墻開啟SSH服務的方法，需要的朋友可以參考下
方法步驟
1、配置FreeBSD 防火墻
ee /etc/rc.conf #編輯，在最后添加
firewall_enable="yes" #開啟防火墻
net.inet.ip.fw.verbose=1 #啟用防火墻日志功能
net.inet.ip.fw.verbose_limit=5 #啟用防火墻日志功能
natd_enable="YES" # 開啟防火墻NAT功能
natd_interface="rl0"
natd_flags="-dynamic -m"
firewall_script="/etc/ipfw.rules" #自定義防火墻規(guī)則路徑
按esc，回車，再按a保存配置
2、添加防火墻規(guī)則
ee /etc/ipfw.rules #編輯防火墻規(guī)則，添加以下代碼
#!/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
$cmd 999 deny log all from any to any
################ End of IPFW rules file ###############################
備注：參數(shù)說明：
#$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(wǎng)，否則主機無法聯(lián)網(wǎng)。
$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(wǎng)絡服務，使防火墻規(guī)則生效
/etc/netstart #重啟網(wǎng)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(guī)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(xiàn)在已經(jīng)可以使用Putty等遠程連接工具連接服務器了。
#####################################################
擴展閱讀：
有兩種加載自定義 ipfw 防火墻規(guī)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(guī)則 文件的完整路徑。
例如：
add allow in
add allow out
firewall_type="open"參數(shù)說明
open ── 允許所有流量通過。
client ── 只保護本機。
simple ── 保護整個網(wǎng)絡。
closed ── 完全禁止除回環(huán)設備之外的全部 IP 流量。
UNKNOWN ── 禁止加載防火墻規(guī)則。
filename ── 到防火墻規(guī)則文件的絕對路徑。
IPFW防火墻規(guī)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(zhí)行腳本， 這樣這個腳本會在啟動時自動執(zhí)行。
補充閱讀：防火墻主要使用技巧
一、所有的防火墻文件規(guī)則必須更改。
盡管這種方法聽起來很容易，但是由于防火墻沒有內置的變動管理流程，因此文件更改對于許多企業(yè)來說都不是最佳的實踐方法。如果防火墻管理員因為突發(fā)情況或者一些其他形式的業(yè)務中斷做出更改，那么他撞到槍口上的可能性就會比較大。但是如果這種更改抵消了之前的協(xié)議更改，會導致宕機嗎?這是一個相當高發(fā)的狀況。
防火墻管理產(chǎn)品的中央控制臺能全面可視所有的防火墻規(guī)則基礎，因此團隊的所有成員都必須達成共識，觀察誰進行了何種更改。這樣就能及時發(fā)現(xiàn)并修理故障，讓整個協(xié)議管理更加簡單和高效。
二、以最小的權限安裝所有的訪問規(guī)則。
另一個常見的安全問題是權限過度的規(guī)則設置。防火墻規(guī)則是由三個域構成的：即源(IP地址)，目的地(網(wǎng)絡/子網(wǎng)絡)和服務(應用軟件或者其他目的地)。為了確保每個用戶都有足夠的端口來訪問他們所需的系統(tǒng)，常用方法是在一個或者更多域內指定打來那個的目標對象。當你出于業(yè)務持續(xù)性的需要允許大范圍的IP地址來訪問大型企業(yè)的網(wǎng)絡，這些規(guī)則就會變得權限過度釋放，因此就會增加不安全因素。服務域的規(guī)則是開放65535個TCP端口的ANY。防火墻管理員真的就意味著為黑客開放了65535個攻擊矢量?
三、根據(jù)法規(guī)協(xié)議和更改需求來校驗每項防火墻的更改。
在防火墻操作中，日常工作都是以尋找問題，修正問題和安裝新系統(tǒng)為中心的。在安裝最新防火墻規(guī)則來解決問題，應用新產(chǎn)品和業(yè)務部門的過程中，我們經(jīng)常會遺忘防火墻也是企業(yè)安全協(xié)議的物理執(zhí)行者。每項規(guī)則都應該重新審核來確保它能符合安全協(xié)議和任何法規(guī)協(xié)議的內容和精神，而不僅是一篇法律條文。
四、當服務過期后從防火墻規(guī)則中刪除無用的規(guī)則。
規(guī)則膨脹是防火墻經(jīng)常會出現(xiàn)的安全問題，因為多數(shù)運作團隊都沒有刪除規(guī)則的流程。業(yè)務部門擅長讓你知道他們了解這些新規(guī)則，卻從來不會讓防火墻團隊知道他們不再使用某些服務了。了解退役的服務器和網(wǎng)絡以及應用軟件更新周期對于達成規(guī)則共識是個好的開始。運行無用規(guī)則的報表是另外一步。黑客喜歡從來不刪除規(guī)則的防火墻團隊。
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