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发信人: ykwch.bbs@bbs.cqupt.edu.cn (心蓝--雨下), 信区: Linux
标 题: 防火墙技术分析讲义--一
发信站: 幽幽黄桷兰 (Sat Apr 5 15:01:59 2003)
转信站: SZU!news.tiaozhan.com!news.happynet.org!CQUPT
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防火墙技术分析讲义
防火墙技术分析讲义
yawl@docshow.net
一 基本概念
1.1 防火墙分类:
包过滤
代理(应用层网关)
1.2 代理:
两个连接(browser与proxy之间,proxy与web server之间)。
工作在应用层。
直接发往服务器的包:
GET / HTTP/1.1
Accept: */*
Accept-Language: zh-cn
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)
Host: www.lisoleg.net
Connection: Keep-Alive
往代理发出的包:
GET http://www.lisoleg.net/ HTTP/1.1
Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, applica
tion/vnd.ms-powerpoint, application/msword, */*
Accept-Language: zh-cn
Accept-Encoding: gzip, deflate
If-Modified-Since: Thu, 14 Dec 2000 07:24:52 GMT
If-None-Match: "8026-185-3a3875c4"
User-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)
Host: www.lisoleg.net
Proxy-Connection: Keep-Alive
增强:
cache
1.3 包过滤
单IP包检测
缺陷:无状态
1.4 增强1-状态检测(Stateful Inspection),又称动态包过滤(dynamic packet fi
ltering)
1.4.1 规则表和动态状态表
1.4.2 ftp的例子:
A 4847->B 21 PORT 192,168,7,60,18,241
B 21->A 4847 PORT command successful.
B 20->A 4849 syn
> A classic example is transferring files using FTP. The firewall re
members the details of the
> incoming request to get a file from an FTP server. The firewall th
en tracks the back-channel
> request (the FTP Port command) by the server for transferring info
rmation back to the client.
> As long as the information agrees (same IP addresses, no changes i
n port numbers, and no
> non-FTP requests), the firewall allows the traffic. After the tran
sfer is complete, the
> firewall closes the ports involved.
1.4.3 两种实现方法:
1.4.3.1 checkpoint FW1,netfilter
1.4.3.2 动态添加规则(ipchains patch)
> I believe it does exactly what I want: Installing a temporary
> "backward"-rule to let packets in as a response to an
> outgoing request.
1.5 增强2-地址转换:
1.5.1 静态NAT
1.5.2 动态NAT
1.5.3 地址伪装
1.6 增强3-VPN:
位置的优越性
--
也许轮回里早已经注定
今生就该我还给你
一颗心在风雨里飘来飘去
只是为你
※ 来源:·幽幽黄桷兰 bbs.cqupt.edu.cn·[FROM: BlueCrystal]
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