編譯自： https://www.cyberciti.biz/faq/how-to-set-up-a-firewall-with-pf-on-freebsd-to-protect-a-web-server/
How To Set Up a Firewall with PF on FreeBSD to Protect a Web Server
我是從 Linux 遷移過來的 FreeBSD 新用戶，Linux 中使用的是 netfilter 防火牆框架（LCTT 譯註：netfilter 是由 Rusty Russell 提出的 Linux 2.4 內核防火牆框架）。那麼在 FreeBSD 上，我該如何設置 PF 防火牆，來保護只有一個公共 IP 地址和端口的 web 服務器呢？
PF 是 包過濾器(packet filter)的簡稱。它是為 OpenBSD 開發的，但是已經被移植到了 FreeBSD 以及其它操作系統上。PF 是一個包狀態過濾引擎。在這篇教程中，我將向你展示如何在 FreeBSD 10.x 以及 11.x 中設置 PF 防火牆，從而來保護 web 服務器。
第一步：開啟 PF 防火牆
你需要把下面這幾行內容添加到文件 /etc/rc.conf 文件中：
# echo 'pf_enable="YES"' >> /etc/rc.conf
# echo 'pf_rules="/usr/local/etc/pf.conf"' >> /etc/rc.conf
# echo 'pflog_enable="YES"' >> /etc/rc.conf
# echo 'pflog_logfile="/var/log/pflog"' >> /etc/rc.conf
在這裡：
- pf_enable="YES" - 開啟 PF 服務
- pf_rules="/usr/local/etc/pf.conf" - 從文件 /usr/local/etc/pf.conf 中讀取 PF 規則
- pflog_enable="YES" - 為 PF 服務打開日誌支持
- pflog_logfile="/var/log/pflog" - 存儲日誌的文件，即日誌存於文件 /var/log/pflog 中
第二步：在 /usr/local/etc/pf.conf 文件中創建防火牆規則
輸入下面這個命令打開文件（超級用戶模式下）：
# vi /usr/local/etc/pf.conf
在文件中添加下面這些 PF 規則集：
# vim: set ft=pf
# /usr/local/etc/pf.conf
## 設置公共端口 ##
ext_if="vtnet0"
## 設置服務器公共 IP 地址 ##
ext_if_ip="172.xxx.yyy.zzz"
## 設置並刪除下面這些公共端口上的 IP 範圍 ##
martians = "{ 127.0.0.0/8, 192.168.0.0/16, 172.16.0.0/12, \
10.0.0.0/8, 169.254.0.0/16, 192.0.2.0/24, \
0.0.0.0/8, 240.0.0.0/4 }"
## 設置 http(80)/https (443) 端口 ##
webports = "{http, https}"
## 啟用下面這些服務 ##
int_tcp_services = "{domain, ntp, smtp, www, https, ftp, ssh}"
int_udp_services = "{domain, ntp}"
## 跳過迴環端口 - 跳過端口上的所有 PF 處理 ##
set skip on lo
## 設置 PF 應該統計的端口信息，如發送/接收字節數，通過/禁止的包的數目 ##
set loginterface $ext_if
## 設置默認策略 ##
block return in log all
block out all
# 基於 IP 分片的錯誤處理來防禦攻擊
scrub in all
# 刪除所有不可達路由地址
block drop in quick on $ext_if from $martians to any
block drop out quick on $ext_if from any to $martians
## 禁止欺騙包
antispoof quick for $ext_if
# 打開 SSH 端口，SSH 服務僅從 VPN IP 139.xx.yy.zz 監聽 22 號端口
# 出於安全原因，我不允許/接收 SSH 流量
pass in quick on $ext_if inet proto tcp from 139.xxx.yyy.zzz to $ext_if_ip port = ssh flags S/SA keep state label "USER_RULE: Allow SSH from 139.xxx.yyy.zzz"
## 使用下面這些規則來為所有來自任何 IP 地址的用戶開啟 SSH 服務 #
## pass in inet proto tcp to $ext_if port ssh
### [ OR ] ###
## pass in inet proto tcp to $ext_if port 22
# Allow Ping-Pong stuff. Be a good sysadmin
pass inet proto icmp icmp-type echoreq
# All access to our Nginx/Apache/Lighttpd Webserver ports
pass proto tcp from any to $ext_if port $webports
# 允許重要的發送流量
pass out quick on $ext_if proto tcp to any port $int_tcp_services
pass out quick on $ext_if proto udp to any port $int_udp_services
# 在下面添加自定義規則
保存並關閉文件。歡迎來參考我的 規則集 。如果要檢查語法錯誤，可以運行：
# service pf check
或
/etc/rc.d/pf check
或
# pfctl -n -f /usr/local/etc/pf.conf
第三步：開始運行 PF 防火牆
命令如下。請小心，如果是基於 SSH 的會話，你可能會和服務器斷開連接。
開啟 PF 防火牆：
# service pf start
停用 PF 防火牆：
# service pf stop
檢查語法錯誤：
# service pf check
重啟服務：
# service pf restart
查看 PF 狀態：
# service pf status
示例輸出：
Status: Enabled for 0 days 00:02:18 Debug: Urgent
Interface Stats for vtnet0 IPv4 IPv6
Bytes In 19463 0
Bytes Out 18541 0
Packets In
Passed 244 0
Blocked 3 0
Packets Out
Passed 136 0
Blocked 12 0
State Table Total Rate
current entries 1
searches 395 2.9/s
inserts 4 0.0/s
removals 3 0.0/s
Counters
match 19 0.1/s
bad-offset 0 0.0/s
fragment 0 0.0/s
short 0 0.0/s
normalize 0 0.0/s
memory 0 0.0/s
bad-timestamp 0 0.0/s
congestion 0 0.0/s
ip-option 0 0.0/s
proto-cksum 0 0.0/s
state-mismatch 0 0.0/s
state-insert 0 0.0/s
state-limit 0 0.0/s
src-limit 0 0.0/s
synproxy 0 0.0/s
map-failed 0 0.0/s
開啟/關閉/重啟 pflog 服務的命令
輸入下面這些命令：
# service pflog start
# service pflog stop
# service pflog restart
第四步：pfctl 命令的簡單介紹
你需要使用 pfctl 命令來查看 PF 規則集和參數配置，包括來自 包過濾器(packet filter)的狀態信息。讓我們來看一下所有常見命令：
顯示 PF 規則信息
# pfctl -s rules
示例輸出：
block return in log all
block drop out all
block drop in quick on ! vtnet0 inet from 172.xxx.yyy.zzz/24 to any
block drop in quick inet from 172.xxx.yyy.zzz/24 to any
pass in quick on vtnet0 inet proto tcp from 139.aaa.ccc.ddd to 172.xxx.yyy.zzz/24 port = ssh flags S/SA keep state label "USER_RULE: Allow SSH from 139.aaa.ccc.ddd"
pass inet proto icmp all icmp-type echoreq keep state
pass out quick on vtnet0 proto tcp from any to any port = domain flags S/SA keep state
pass out quick on vtnet0 proto tcp from any to any port = ntp flags S/SA keep state
pass out quick on vtnet0 proto tcp from any to any port = smtp flags S/SA keep state
pass out quick on vtnet0 proto tcp from any to any port = http flags S/SA keep state
pass out quick on vtnet0 proto tcp from any to any port = https flags S/SA keep state
pass out quick on vtnet0 proto tcp from any to any port = ftp flags S/SA keep state
pass out quick on vtnet0 proto tcp from any to any port = ssh flags S/SA keep state
pass out quick on vtnet0 proto udp from any to any port = domain keep state
pass out quick on vtnet0 proto udp from any to any port = ntp keep state
顯示每條規則的詳細內容
# pfctl -v -s rules
在每條規則的詳細輸出中添加規則編號：
# pfctl -vvsr show
顯示狀態信息
# pfctl -s state
# pfctl -s state | more
# pfctl -s state | grep 'something'
如何在命令行中禁止 PF 服務
# pfctl -d
如何在命令行中啟用 PF 服務
# pfctl -e
如何在命令行中刷新 PF 規則/NAT/路由表
# pfctl -F all
示例輸出：
rules cleared
nat cleared
0 tables deleted.
2 states cleared
source tracking entries cleared
pf: statistics cleared
pf: interface flags reset
如何在命令行中僅刷新 PF 規則
# pfctl -F rules
如何在命令行中僅刷新隊列
# pfctl -F queue
如何在命令行中刷新統計信息（它不是任何規則的一部分）
# pfctl -F info
如何在命令行中清除所有計數器
# pfctl -z clear
第五步：查看 PF 日誌
PF 日誌是二進制格式的。使用下面這一命令來查看：
# tcpdump -n -e -ttt -r /var/log/pflog
示例輸出：
Aug 29 15:41:11.757829 rule 0/(match) block in on vio0: 86.47.225.151.55806 > 45.FOO.BAR.IP.23: S 757158343:757158343(0) win 52206 [tos 0x28]
Aug 29 15:41:44.193309 rule 0/(match) block in on vio0: 5.196.83.88.25461 > 45.FOO.BAR.IP.26941: S 2224505792:2224505792(0) ack 4252565505 win 17520 (DF) [tos 0x24]
Aug 29 15:41:54.628027 rule 0/(match) block in on vio0: 45.55.13.94.50217 > 45.FOO.BAR.IP.465: S 3941123632:3941123632(0) win 65535
Aug 29 15:42:11.126427 rule 0/(match) block in on vio0: 87.250.224.127.59862 > 45.FOO.BAR.IP.80: S 248176545:248176545(0) win 28200
(DF) Aug 29 15:43:04.953537 rule 0/(match) block in on vio0: 77.72.82.22.47218 > 45.FOO.BAR.IP.7475: S 1164335542:1164335542(0) win 1024
Aug 29 15:43:05.122156 rule 0/(match) block in on vio0: 77.72.82.22.47218 > 45.FOO.BAR.IP.7475: R 1164335543:1164335543(0) win 1200
Aug 29 15:43:37.302410 rule 0/(match) block in on vio0: 94.130.12.27.18080 > 45.FOO.BAR.IP.64857: S 683904905:683904905(0) ack 4000841729 win 16384
Aug 29 15:44:46.574863 rule 0/(match) block in on vio0: 77.72.82.22.47218 > 45.FOO.BAR.IP.7677: S 3451987887:3451987887(0) win 1024
Aug 29 15:44:46.819754 rule 0/(match) block in on vio0: 77.72.82.22.47218 > 45.FOO.BAR.IP.7677: R 3451987888:3451987888(0) win 1200
Aug 29 15:45:21.194752 rule 0/(match) block in on vio0: 185.40.4.130.55910 > 45.FOO.BAR.IP.80: S 3106068642:3106068642(0) win 1024
Aug 29 15:45:32.999219 rule 0/(match) block in on vio0: 185.40.4.130.55910 > 45.FOO.BAR.IP.808: S 322591763:322591763(0) win 1024
Aug 29 15:46:30.157884 rule 0/(match) block in on vio0: 77.72.82.22.47218 > 45.FOO.BAR.IP.6511: S 2412580953:2412580953(0) win 1024 [tos 0x28]
Aug 29 15:46:30.252023 rule 0/(match) block in on vio0: 77.72.82.22.47218 > 45.FOO.BAR.IP.6511: R 2412580954:2412580954(0) win 1200 [tos 0x28]
Aug 29 15:49:44.337015 rule 0/(match) block in on vio0: 189.219.226.213.22640 > 45.FOO.BAR.IP.23: S 14807:14807(0) win 14600 [tos 0x28]
Aug 29 15:49:55.161572 rule 0/(match) block in on vio0: 5.196.83.88.25461 > 45.FOO.BAR.IP.40321: S 1297217585:1297217585(0) ack 1051525121 win 17520 (DF) [tos 0x24]
Aug 29 15:49:59.735391 rule 0/(match) block in on vio0: 36.7.147.209.2545 > 45.FOO.BAR.IP.3389: SWE 3577047469:3577047469(0) win 8192
(DF) [tos 0x2 (E)] Aug 29 15:50:00.703229 rule 0/(match) block in on vio0: 36.7.147.209.2546 > 45.FOO.BAR.IP.3389: SWE 1539382950:1539382950(0) win 8192
(DF) [tos 0x2 (E)] Aug 29 15:51:33.880334 rule 0/(match) block in on vio0: 45.55.22.21.53510 > 45.FOO.BAR.IP.2362: udp 14
Aug 29 15:51:34.006656 rule 0/(match) block in on vio0: 77.72.82.22.47218 > 45.FOO.BAR.IP.6491: S 151489102:151489102(0) win 1024 [tos 0x28]
Aug 29 15:51:34.274654 rule 0/(match) block in on vio0: 77.72.82.22.47218 > 45.FOO.BAR.IP.6491: R 151489103:151489103(0) win 1200 [tos 0x28]
Aug 29 15:51:36.393019 rule 0/(match) block in on vio0: 60.191.38.78.4249 > 45.FOO.BAR.IP.8000: S 3746478095:3746478095(0) win 29200 (DF)
Aug 29 15:51:57.213051 rule 0/(match) block in on vio0: 24.137.245.138.7343 > 45.FOO.BAR.IP.5358: S 14134:14134(0) win 14600
Aug 29 15:52:37.852219 rule 0/(match) block in on vio0: 122.226.185.125.51128 > 45.FOO.BAR.IP.23: S 1715745381:1715745381(0) win 5840
(DF) Aug 29 15:53:31.309325 rule 0/(match) block in on vio0: 189.218.148.69.377 > 45.FOO.BAR.IP5358: S 65340:65340(0) win 14600 [tos 0x28]
Aug 29 15:53:31.809570 rule 0/(match) block in on vio0: 13.93.104.140.53184 > 45.FOO.BAR.IP.1433: S 39854048:39854048(0) win 1024
Aug 29 15:53:32.138231 rule 0/(match) block in on vio0: 13.93.104.140.53184 > 45.FOO.BAR.IP.1433: R 39854049:39854049(0) win 1200
Aug 29 15:53:41.459088 rule 0/(match) block in on vio0: 77.72.82.22.47218 > 45.FOO.BAR.IP.6028: S 168338703:168338703(0) win 1024
Aug 29 15:53:41.789732 rule 0/(match) block in on vio0: 77.72.82.22.47218 > 45.FOO.BAR.IP.6028: R 168338704:168338704(0) win 1200
Aug 29 15:54:34.993594 rule 0/(match) block in on vio0: 212.47.234.50.5102 > 45.FOO.BAR.IP.5060: udp 408 (DF) [tos 0x28]
Aug 29 15:54:57.987449 rule 0/(match) block in on vio0: 51.15.69.145.5100 > 45.FOO.BAR.IP.5060: udp 406 (DF) [tos 0x28]
Aug 29 15:55:07.001743 rule 0/(match) block in on vio0: 190.83.174.214.58863 > 45.FOO.BAR.IP.23: S 757158343:757158343(0) win 27420
Aug 29 15:55:51.269549 rule 0/(match) block in on vio0: 142.217.201.69.26112 > 45.FOO.BAR.IP.22: S 757158343:757158343(0) win 22840
Aug 29 15:58:41.346028 rule 0/(match) block in on vio0: 169.1.29.111.29765 > 45.FOO.BAR.IP.23: S 757158343:757158343(0) win 28509
Aug 29 15:59:11.575927 rule 0/(match) block in on vio0: 187.160.235.162.32427 > 45.FOO.BAR.IP.5358: S 22445:22445(0) win 14600 [tos 0x28]
Aug 29 15:59:37.826598 rule 0/(match) block in on vio0: 94.74.81.97.54656 > 45.FOO.BAR.IP.3128: S 2720157526:2720157526(0) win 1024 [tos 0x28]stateful
Aug 29 15:59:37.991171 rule 0/(match) block in on vio0: 94.74.81.97.54656 > 45.FOO.BAR.IP.3128: R 2720157527:2720157527(0) win 1200 [tos 0x28]
Aug 29 16:01:36.990050 rule 0/(match) block in on vio0: 182.18.8.28.23299 > 45.FOO.BAR.IP.445: S 1510146048:1510146048(0) win 16384
如果要查看實時日誌，可以運行：
# tcpdump -n -e -ttt -i pflog0
如果你想了解更多信息，可以訪問 PF FAQ 和 FreeBSD HANDBOOK 以及下面這些 man 頁面：
# man tcpdump
# man pfctl
# man pf
關於作者
我是 nixCraft 的創立者，一個經驗豐富的系統管理員，同時也是一位 Linux 操作系統/Unix shell 腳本培訓師。我在不同的行業與全球客戶工作過，包括 IT、教育、國防和空間研究、以及非營利組織。你可以在 Twitter 、 Facebook 或 Google+ 上面關注我。
via: https://www.cyberciti.biz/faq/how-to-set-up-a-firewall-with-pf-on-freebsd-to-protect-a-web-server/
本文由 LCTT 原創編譯， Linux中國 榮譽推出
閱讀更多 Linux中國 的文章
