How to better defend against CC attacks under Linux

1. Install dependent packages:

yum install perl-libwww-perl perl iptables

2. Download and install CSF:

wget https://download.configserver.com/csf.tgz
tar -xzf csf.tgz
cd csf
sh install.sh

3. Test whether CSF is Can work normally:

root@localhost csf]# perl /etc/csf/csftest.pl
Testing ip_tables/iptable_filter...OK
Testing ipt_LOG...OK
Testing ipt_multiport/xt_multiport...OK
Testing ipt_REJECT...OK
Testing ipt_state/xt_state...OK
Testing ipt_limit/xt_limit...OK
Testing ipt_recent...OK
Testing xt_connlimit...OK
Testing ipt_owner/xt_owner...OK
Testing iptable_nat/ipt_REDIRECT...OK
Testing iptable_nat/ipt_DNAT...OK
RESULT: csf should function on this server

4. csf configuration:
The configuration file of CSF is

vim /etc/csf/csf.conf
# Allow incoming TCP ports
# 推荐您更改 SSH 的默认端口（22）为其他端口，但请注意一定要把新的端口加到下一行中
TCP_IN = “20,21,47,81,1723,25,53,80,110,143,443,465,587,993,995〃
# Allow outgoing TCP ports同上，把 SSH 的登录端口加到下一行。
# 在某些程序要求打开一定范围的端口的情况下，例如Pureftpd的passive mode，可使用类似 30000:35000 的方式打开30000-35000范围的端口。
TCP_OUT = “20,21,47,81,1723,25,53,80,110,113,443〃
# Allow incoming UDP ports
UDP_IN = “20,21,53〃
# Allow outgoing UDP ports
# To allow outgoing traceroute add 33434:33523 to this list
UDP_OUT = “20,21,53,113,123〃
# Allow incoming PING 是否允许别人ping你的服务器，默认为1，允许。0为不允许。
ICMP_IN = “1〃
以上这些配置大家一看就懂了，下面再介绍几个比较常用的：
免疫某些类型的小规模 DDos 攻击：
# Connection Tracking. This option enables tracking of all connections from IP
# addresses to the server. If the total number of connections is greater than
# this value then the offending IP address is blocked. This can be used to help
# prevent some types of DOS attack.
#
# Care should be taken with this option. It’s entirely possible that you will
# see false-positives. Some protocols can be connection hungry, e.g. FTP, IMAPD
# and HTTP so it could be quite easy to trigger, especially with a lot of
# closed connections in TIME_WAIT. However, for a server that is prone to DOS
# attacks this may be very useful. A reasonable setting for this option might
# be arround 200.
#
# To disable this feature, set this to 0
CT_LIMIT = "200"##固定时间内同一个IP请求的此数
# Connection Tracking interval. Set this to the the number of seconds between
# connection tracking scans
CT_INTERVAL = "30" ##指上面的固定时间，单位为秒
# Send an email alert if an IP address is blocked due to connection tracking
CT_EMAIL_ALERT = "1" ##是否发送邮件
# If you want to make IP blocks permanent then set this to 1, otherwise blocks
# will be temporary and will be cleared after CT_BLOCK_TIME seconds
# 是否对可疑IP采取永久屏蔽，默认为0，即临时性屏蔽。
CT_PERMANENT = "0"
# If you opt for temporary IP blocks for CT, then the following is the interval
# in seconds that the IP will remained blocked for (e.g. 1800 = 30 mins)
# 临时性屏蔽时间
CT_BLOCK_TIME = "1800"
# If you don’t want to count the TIME_WAIT state against the connection count
# then set the following to “1〃
CT_SKIP_TIME_WAIT = "0" ##是否统计TIME_WAIT链接状态
# If you only want to count specific states (e.g. SYN_RECV) then add the states
# to the following as a comma separated list. E.g. “SYN_RECV,TIME_WAIT”
# Leave this option empty to count all states against CT_LIMIT
CT_STATES = "" ##是否分国家来统计，填写的是国家名
# If you only want to count specific ports (e.g. 80,443) then add the ports
# to the following as a comma separated list. E.g. “80,443〃
#
# Leave this option empty to count all ports against CT_LIMIT
# 对什么端口进行检测，为空则检测所有，防止ssh的话可以为空，统计所有的。
CT_PORTS = ""
做了以上设置之后，可以先测试一下。如果没有问题的话，就更改为正式模式，刚才只是测试模式。
# 把默认的1修改为0。
TESTING = "0"
在/etc/csf/下有csf.allow和csf.deny两个文件，
allow是信任的IP，可以把自己的IP写到这里面防止误封。
deny就是被封的IP。

If there is any adjustment Need to restart the cfs service

#If there is an error in downloading the csf installation package in the second step, please move Step

https://www.configserver.com/ Officially download the latest installation package;

About csf(); More specific instructions on usage and functional methods are more detailed on the official website. This article mainly understands How to better defend against CC attacks under Linux;

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