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网络过滤 - 透明防火墙架设的完全攻略(bridge+iptables+squid)

透明防火墙架设的完全攻略(bridge+iptables+squid)
2004-04-23 15:18 pm
来自:Linux文档
现载:Www.8s8s.coM
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架设透明代理和防火墙是linux平台上很热的话题,在水木上也有相关文章,但完全的攻略在公网上也很少,最近架了一台,前后花去一个多星期(我这人手脚慢,别笑,中间笑话也颇多)觉得还是把过程写下来的好,可以让人依葫芦画瓢。

先把网络环境说一下,一个200人左右的局域网,一个C class,一台路由器做NAT(一个公网ip)。网络环境还是很简单的,目的就是在路由器和局域网间加一台透明防火墙进去,同时完成cache server的功能。我不想让防火墙做nat,一是因为已经有了一台路由器,要物尽其用。二是 nat其实也是很耗资源的事(尤其当下面的clients特别多时,对router cpu的要求还是很高的,我就碰到过一台cisco 75XX 路由器拖1000个用户5分钟死一次机的事,后来不得已架了一台PIX做NAT)还是分分开的好。三是万一cache server 趴下了,只要把链路重新旁接一下,网络照样用(顶多性能不好),不会影响用户。

防火墙的平台为一P4 2.4G server, 512M内存,2×80GHD,两块NIC。安装的是RH8.0 kernel 2.4.20(原来想装gentoo的,但要命的1.4到现在才刚到RC3,等不及了,偷了一把懒~_~)

先下载bridge做桥接,bridge的作用就是让两块网卡变成一个桥设备,让两端的网络端口完全透明地转发packets,而让 iptables起到blocking的作用。下载地址为http://bridge.sourceforge.net(什么?sourceforge?不知道上不去啊!没办法,因为众所周知的原因,大伙找https proxy绕上去吧!)需下载bridge-utils-0.9.6.tar.gz和 bridge-nf-0.0.7-against-2.4.19.diff。(这个很重要,否则iptables无法拦截转发过来的packets)

再到http://netfilter.samba.org下载iptables,并到www.linuxhq.xom下载最新的kernel及patch。

在/usr/src下释放kernel,进入/usr/src/linux,并把bridge的patch打上,patch –p1 < bridge-nf-0.0.7-against-2.4.19.diff.

最后还有个问题,此时用ifconfig看到的流量,在过了4G之后就会被置0,然后从头开始,很不爽。这是因为 'RX bytes' and 'TX bytes'等变量的数据类型为 unsigned long,即2^32,到了4G就重置,其实把它们改成 unsigned long long(2^64)就可以了。更改
/usr/src/linux/include/linux/netdevice.h 和../linux/net/core/dev.c,以下是打patch时的记录,找到文件改掉相应代码即可。

diff -urN linux-orig/include/linux/netdevice.h linux/include/linux/netdevice.h
--- linux-orig/include/linux/netdevice.h
+++ linux/include/linux/netdevice.h
@@ -96,10 +96,10 @@


struct net_device_stats
{
- unsigned long rx_packets; /* total packets received */
- unsigned long tx_packets; /* total packets transmitted */
- unsigned long rx_bytes; /* total bytes received */
- unsigned long tx_bytes; /* total bytes transmitted */
+ unsigned long long rx_packets; /* total packets received */
+ unsigned long long tx_packets; /* total packets transmitted */
+ unsigned long long rx_bytes; /* total bytes received */
+ unsigned long long tx_bytes; /* total bytes transmitted */
unsigned long rx_errors; /* bad packets received */
unsigned long tx_errors; /* packet transmit problems */
unsigned long rx_dropped; /* no space in linux buffers */

diff -urN linux-orig/net/core/dev.c linux/net/core/dev.c
--- linux-orig/net/core/dev.c
+++ linux/net/core/dev.c
@@ -1689,7 +1689,7 @@
int size;


if (stats)
- size = sprintf(buffer, "%6s:%8lu %7lu %4lu %4lu %4lu %5lu %10lu %9lu %8lu %7lu %4lu %4lu %4lu %5lu %7lu %10lu ",
+ size = sprintf(buffer, "%6s:%8llu %7llu %4lu %4lu %4lu %5lu %10lu %9lu %8llu %7llu %4lu %4lu %4lu %5lu %7lu %10lu ",
dev->name,
stats->rx_bytes,
stats->rx_packets, stats->rx_errors,

这样编译后,ifconfig的4G重置问题就被消除了。

下面就是重新编译kernel了,make menuconfig.....
注意,除了要把该编译进去的驱动编进去(象NIC什么的,我第一次编时就漏了一块网卡,汗ing)还要把最重要的iptables给enable 起来,进入Network Options,选中Network Packet filtering (replaces ipchains),这样就会打开IP: Netfilter Configuration --> 子菜单,进入,选中里面所有的选项,然后回到 Network Options菜单,选中“802.1d Ethernet Bridging” 和 “netfilter (firewalling) support”两个选项(一看就知道很重要。)
退出,开编。
make dep
make modules
make modules_install
make bzImage
完成后cp /usr/src/linux/arch/i386/bzImage /boot/bzImage.bridge
然后把System.map拷至/boot下再在lilo或grub中更改相应配置即可(这就不细说了,重编kernel的文章到处都有。)

重起,如果正常,开始下一步,tar –xzvf bridge-utils-0.9.6.tar.gz.
cd ./bridge-utils-0.9.3
make
make install(编译bridge并安装,具体的安装目录可在make文件生成时指定。)
完毕后可以先试试bridge的基本命令。如brctl addbr mybridge (创建bridge mybridge,然后用ifconfig查看会发现多了一个mybridge端口)
brctl addif mybridge eth0
brctl addif mybridge eth1 (把eth0和eth1包含到mybridge中)
然后需要对各端口做以下动作
ifconfig eth0 0.0.0.0 promisc
ifconfig eth1 0.0.0.0 promisc(打开混杂模式)
这时桥接即已成功,从router和局域网转发过来的消息开始通过机器,这时你会发觉满屏的tcp/ip转发消息让你无法下手,硬盘也狂转,这是 syslogd和klogd做的怪,log的priviledge设得太低,改掉它。telnet 进入机器(这时你只能telnet,console上已经泛滥成灾。)kill 掉syslogd和klogd,在/etc/syslog.conf中屏蔽掉*.info至 /var/log/messages的rules(一开始我不知道这个,结果第一天下午连到网络上去,第二天上午一看,/var/log下的 messages居然有2.7G,My God),并修改/etc/init.d/syslog,在daemon klogd 一项后加上-2 -c 4 (提高klogd的消息转发级别),重起syslogd,哈哈,整个世界清净了!!!

其实我们也可以写个启动脚本放在/etc/init.d中,如下:
#!/bin/bash

. /etc/init.d/functions


return=$rc_done


start() {
echo "Starting service bridge tranfw"
brctl addbr tranfw || return=$rc_failed
brctl addif tranfw eth0 || return=$rc_failed
brctl addif tranfw eth1 || return=$rc_failed
ifconfig eth0 0.0.0.0 promisc || return=$rc_failed
ifconfig eth1 0.0.0.0 promisc || return=$rc_failed
brctl sethello tranfw 1 || return=$rc_failed
brctl setmaxage tranfw 4 || return=$rc_failed
brctl setfd tranfw 4 || return=$rc_failed
ifconfig tranfw 192.168.9.11 broadcast 192.168.9.255 promisc up || return=$rc_failed
/sbin/route add default gw 192.168.9.1 netmask 0.0.0.0 metric 1
echo -e "$return"
}

stop() {
echo "Shutting down service bridge tranfw"
brctl delif tranfw eth0 || return=$rc_failed
brctl delif tranfw eth1 || return=$rc_failed
brctl delbr tranfw || return=$rc_failed
echo -e "$return"
}

status(){
ifconfig tranfw
brctl show tranfw
}

restart(){
$0 stop && $0 start || return=$rc_failed
}

case "$1" in
start)
start
;;
stop)
stop
;;
restart)
restart
;;
status)
status tranfw
RETVAL=$?
;;
*)
echo $"Usage: $0 {start|stop|status|restart}"
RETVAL=1

esac

exit $RETVAL

这样启动时就自己起来了。

下一步,我们可以开始配iptables了
tar –xjvf iptables-1.2.7.tar.bz2
cd ./iptables-1.2.7
make
make install
安装很简单。关键是如何用,我懒,抄了个脚本就开用了,如下:
#!/bin/bash
#Flush all rules from the chains
iptables -F
#Delete all user created chains (mainly KEEP_STATE chain)
iptables -X

#############################################################
##Create special chain KEEP_STATE
iptables -N KEEP_STATE
iptables -F KEEP_STATE
##Drop bad states
iptables -A KEEP_STATE -m state --state INVALID -j DROP
iptables -A KEEP_STATE -m state --state RELATED,ESTABLISHED -j ACCEPT
#############################################################

#Drop RST/ACKs to limit OS detection through pinging
iptables -A FORWARD -p tcp --tcp-flags RST RST,ACK -m limit --limit 5/minute -j LOG --log-level notice --log-prefix "RST/ACK: "
iptables -A FORWARD -p tcp --tcp-flags RST RST,ACK -j DROP

#Deny pings from outside
iptables -A FORWARD -p icmp --icmp-type 0/0 -d 192.168.9.0/24 -j ACCEPT
iptables -A FORWARD -p icmp --icmp-type 0/0 -m limit --limit 5/minute -j LOG --log-level notice --log-prefix "Drop Echo Reply: "
iptables -A FORWARD -p icmp --icmp-type 0/0 -j DROP

#Drop potential SQL Worm
iptables -A FORWARD -p tcp -s 192.168.9.0/24 --dport 1433 -j ACCEPT
iptables -A FORWARD -p tcp --dport 1433 -m limit --limit 5/minute -j LOG --log-level notice --log-prefix "Possible SQL Worm: "
iptables -A FORWARD -p tcp --dport 1433 -j DROP

#Pass all boxes to the keep_state chain
iptables -A FORWARD -j KEEP_STATE

######################################################################
##Set up UDP
#Outgoing Traceroute
iptables -A FORWARD -p udp -s 192.168.9.0/24 --sport 32769:65535 --dport 33434:33523 -j ACCEPT

#Incoming Traceroute
iptables -A FORWARD -p udp -s 192.168.9.0/24 --dport 32769:65535 --sport 33434:33523 -j ACCEPT

#Time exceeded
iptables -A FORWARD -p udp -s 192.168.9.0/24 --dport 11 -j ACCEPT

#Port not found
iptables -A FORWARD -p udp -s 192.168.9.0/24 --dport 3 -j ACCEPT

#DNS
iptables -A FORWARD -p udp -s 192.168.9.0/24 --dport 53 -j ACCEPT

#SNMP
iptables -A FORWARD -p udp -s 192.168.9.0/24 --dport 161 -j ACCEPT

#DHCP
iptables -A FORWARD -p udp -s 192.168.9.0/24 --sport 68 --dport 67 -j ACCEPT

#Time Server
iptables -A FORWARD -p udp -s 192.168.9.0/24 --sport 1024:65535 --dport 123 -j ACCEPT

######################################################################
##Allow outward browsing
iptables -A FORWARD -p tcp -s 192.168.9.0/24 --dport 80 -j ACCEPT

##Allow outward ssh
iptables -A FORWARD -p tcp -s 192.168.9.0/24 --dport 22 -j ACCEPT

##Allow outward ftp
iptables -A FORWARD -p tcp -s 192.168.9.0/24 --dport 21 -j ACCEPT

##Allow outward telnet
iptables -A FORWARD -p tcp -s 192.168.9.0/24 --dport 23 -j ACCEPT

##Allow outward smtp
iptables -A FORWARD -p tcp -s 192.168.9.0/24 --dport 25 -j ACCEPT

##Allow outward pop
iptables -A FORWARD -p tcp -s 192.168.9.0/24 --dport 110 -j ACCEPT

###Block HTTP Request from outside that are not authorized
iptables -A FORWARD -p tcp --dport 80 -j DROP
iptables -A FORWARD -p tcp --dport 80 -m limit --limit 5/minute -j LOG --log-level notice --log-prefix "Dropped HTTP: "

#Allow Telnet out
iptables -A FORWARD -p tcp -s 192.168.9.0/24 --dport 23 -j ACCEPT

#Deny ports
##telnet
iptables -A FORWARD -p tcp --dport 23 -m limit --limit 5/minute -j LOG --log-level notice --log-prefix "Denied Telnet: "

#Deny ports
##telnet
iptables -A FORWARD -p tcp --dport 23 -m limit --limit 5/minute -j LOG --log-level notice --log-prefix "Denied Telnet: "
iptables -A FORWARD -p tcp --dport 23 -j DROP

##Deny BO
iptables -A FORWARD -p udp --dport 31337 -m limit --limit 5/minute -j LOG --log-level notice --log-prefix "Denied BO: "
iptables -A FORWARD -p udp --dport 31337 -j DROP

#Deny and log ftp on all others
#iptables -A FORWARD -p tcp -s 192.168.9.0/24 --dport 21 -j DROP
#iptables -A FORWARD -p tcp --dport 21 -m limit --limit 5/minute -j LOG --log-level notice --log-prefix "Denied FTP: "

#Deny suspicious traffic
iptables -A FORWARD -p tcp --destination-port 1080 -j DROP
iptables -A FORWARD -p tcp --destination-port 8080 -j DROP
iptables -A FORWARD -p tcp --destination-port 8000 -j DROP
iptables -A FORWARD -p tcp --destination-port 8081 -j DROP

##Allow all outgoing traffic
iptables -t nat -A PREROUTING -p tcp --dport 80 -j REDIRECT --to-ports 3128 (转发至squid)
iptables -A FORWARD -s 192.168.9.0/24 -j ACCEPT

#Set to drop all packets not accepted by rules above
iptables -A FORWARD -j DROP

也把它放到/etc/init.d中,这样就可以随着xinet.d一起启动了。iptables的语法这里就不详细说了,网上很多。

最后就是squid的配置,这需要仔细说一下,随RH发布的squid的配置有问题,性能受限。建议先卸除,到www.squid-cache.org下载最新的2.5stable1。然后重新编译,编译前需做以下准备工作:
1。编辑/usr/include/bits/types.h中__FD_SETSIZE值至32768
2。ulimit -HSn 32768
然后到squid src包目录编译squid ,./configure, make all, make install.....
squid会安装在缺省的/usr/local/squid下,squid的可执行文件在安装目录的bin子目录下,配置文件在etc子目录下

Squid配置文件为:/usr/local/squid/etc/squid.conf,以下为我的配置:
http_port 8080
cache_mem 32 MB
cache_swap_low 90
cache_swap_high 95
maximum_object_size 4096 KB
cache_dir ufs /usr/local/squid/cache 10000 16 256
cache_access_log /usr/local/squid/logs/access.log
cache_log /usr/local/squid/logs/cache.log
dns_nameservers 202.96.209.5
unlinkd_program /usr/local/squid/bin/unlinkd
acl acllist src 192.168.9.0/255.255.255.0
acl regular_days time MTWHF 8:00-19:00
acl movie urlpath_regex "/etc/squid/banned.list"(把过滤关键字写到文件中去)
acl banned url_regex iij4u.or.jp(做些控制)
acl cache_prevent1 url_regex cgi-bin /?
acl cache_prevent2 url_regex Servlet
acl all src 0.0.0.0/0.0.0.0
acl manager proto cache_object
acl localhost src 127.0.0.1/255.255.255.255
acl SSL_ports port 443 563
acl Safe_ports port 80 # http
acl Safe_ports port 21 # ftp
acl Safe_ports port 443 563 # https, snews
acl Safe_ports port 70 # gopher
acl Safe_ports port 210 # wais
acl Safe_ports port 1025-65535 # unregistered ports
acl Safe_ports port 280 # http-mgmt
acl Safe_ports port 488 # gss-http
acl Safe_ports port 591 # filemaker
acl Safe_ports port 777 # multiling http
http_access deny movie regular_days
no_cache deny cache_prevent1
no_cache deny cache_prevent2
http_access deny banned
http_access allow all
http_access deny !Safe_ports
http_access deny CONNECT !SSL_ports
icp_access allow all
http_access allow manager localhost
http_access deny manager
http_access allow localhost
http_access deny all
client_lifetime 2 hours
half_closed_clients off
cache_effective_user squid
cache_effective_group squid(请注意squid对cache及log目录有读写权)
httpd_accel_host virtual
httpd_accel_port 80
httpd_accel_with_proxy on
httpd_accel_uses_host_header on

同时在/etc/init.d中的启动脚本里加上这句ulimit -HSn 32768
这样squid启动时在cache.log中就可以看到如此语句:
2003/03/05 09:30:53| Starting Squid Cache version 2.5.STABLE1-20030303 for i686-pc-linux-gnu...
2003/03/05 09:30:53| Process ID 12939
2003/03/05 09:30:53| With 32768 file descriptors available

此时的squid拥有32768个file descriptors(缺省为1024),如果用户很多,缺省值会成为瓶颈,极度影响squid的速度(它会报错说running out of file descriptors),我曾经在板上发问,结果没人理我(,还是自力更生,丰衣足食。

启动squid:/usr/local/squid/bin/squid -D

大功告成!整个出internet的http流量就全朝squid走了,用户不知道,同时又可完成封锁的功能。

好辛苦啊!