原文链接
CC攻击很容易发起，并且几乎不需要成本，导致现在的CC攻击越来越多。
大部分搞CC攻击的人，都是用在网上下载的工具，这些工具很少去伪造特征，所以会留下一些痕迹。
使用下面的命令，可以分析下是否在被CC攻击。
第一条命令：
tcpdump-s0 -A -n -i any | grep -o -E '(GET|POST|HEAD) .*'
正常的输出结果类似于这样
POST /ajax/validator.PHPHTTP/1.1
POST /api_redirect.phpHTTP/1.1
GET /team/57085.html HTTP/1.1
POST /order/pay.php HTTP/1.1
GET /static/goodsimg/20140324/1_47.jpg HTTP/1.1
GET /static/theme/qq/css/index.css HTTP/1.1
GET /static/js/index.js HTTP/1.1
GET /static/js/customize.js HTTP/1.1
GET /ajax/loginjs.php?type=topbar& HTTP/1.1
GET /static/js/jQuery.js HTTP/1.1
GET /ajax/load_team_time.php?team_id=57085 HTTP/1.1
GET /static/theme/qq/css/index.css HTTP/1.1
GET /static/js/lazyload/jquery.lazyload.min.js HTTP/1.1
GET /static/js/MSIE.PNG.js HTTP/1.1
GET /static/js/index.js HTTP/1.1
GET /static/js/customize.js HTTP/1.1
GET /ajax/loginjs.php?type=topbar& HTTP/1.1
GET /static/theme/qq/css/i/logo.jpg HTTP/1.1
GET /static/theme/qq/css/i/logos.png HTTP/1.1
GET /static/theme/qq/css/i/hot.gif HTTP/1.1
GET /static/theme/qq/css/i/brand.gif HTTP/1.1
GET /static/theme/qq/css/i/new.gif HTTP/1.1
GET /static/js/jquery.js HTTP/1.1
GET /static/theme/qq/css/i/logo.jpg HTTP/1.1
正常命令结果以静态文件为主，比如css,js,各种图片。
如果是被攻击，会出现大量固定的地址，比如攻击的是首页，会有大量的“GET / HTTP/1.1”，或者有一定特征的地址，比如攻击的如何是Discuz论坛，那么可能会出现大量的“/thread-随机数字-1-1.html”这样的地址。
第二条命令：
tcpdump -s0 -A -n -i any | grep ^User-Agent
输出结果类似于下面：
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)
User-Agent: Mozilla/5.0 (Windows NT 5.1) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/21.0.1180.89 Safari/537.1
User-Agent: Mozilla/5.0 (Windows NT 5.1) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/21.0.1180.89 Safari/537.1
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)
User-Agent: Mozilla/5.0 (Windows NT 5.1) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/21.0.1180.89 Safari/537.1
User-Agent: Mozilla/5.0 (Windows NT 5.1) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/21.0.1180.89 Safari/537.1
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727; 360space)
User-Agent: Mozilla/5.0 (Windows NT 5.1) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/21.0.1180.89 Safari/537.1
User-Agent: Mozilla/5.0 (Windows NT 5.1) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/21.0.1180.89 Safari/537.1
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727; 360space)
User-Agent: Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)
User-Agent: Mozilla/5.0 (Windows NT 5.1) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/21.0.1180.89 Safari/537.1
User-Agent: Mozilla/5.0 (Windows NT 5.1) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/21.0.1180.89 Safari/537.1
User-Agent: Mozilla/5.0 (Windows NT 5.1) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/21.0.1180.89 Safari/537.1
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)
User-Agent: Mozilla/5.0 (Windows NT 5.1) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/21.0.1180.89 Safari/537.1
User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0)
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)
User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727; InfoPath.2)
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)
这个是查看客户端的useragent，正常的结果中，是各种各样的useragent。
大多数攻击使用的是固定的useragent，也就是会看到同一个useragent在刷屏。随机的useragent只见过一次，但是给搞成了类似于这样“axd5m8usy”，还是可以分辨出来。
第三条命令：
tcpdump -s0 -A -n -i any | grep ^Host
如果机器上的网站太多，可以用上面的命令找出是哪个网站在被大量请求
输出结果类似于下面这样
Host:www.server110.com
Host:www.server110.com
Host:www.server110.com
Host: upload.server110.com
Host: upload.server110.com
Host: upload.server110.com
Host: upload.server110.com
Host: upload.server110.com
Host: upload.server110.com
Host: upload.server110.com
Host: upload.server110.com
Host: upload.server110.com
Host:www.server110.com
Host: upload.server110.com
Host: upload.server110.com
Host: upload.server110.com
Host:www.server110.com
Host:www.server110.com
Host: upload.server110.com
Host: upload.server110.com
Host: upload.server110.com
Host:www.server110.com
Host: upload.server110.com
Host: upload.server110.com
Host:www.server110.com
一般系统不会默认安装tcpdump命令
centos安装方法：yum install -y tcpdump
debian/ubuntu安装方法：apt-get install -y tcpdump
很多小白用户不懂得如何设置日志，查看日志，使用上面的命令则简单的多，复制到命令行上运行即可。
原文链接
