Snmpd Listen to Specific IP Address - CentOS

 

vi /etc/sysconfig/snmpd.options

OPTIONS="-Lsd -Lf /dev/null -p /var/run/snmpd.pid -a -x 127.0.0.1 192.168.1.254"

service snmpd reload

 

 

Enable Service in centos 9 firewall (firewalld)

 

1. 1. Add a profile for SNMP to firewalld.

      nano /etc/firewalld/services/snmp.xml

      Contents of the file is as following (Please mind the using of udp port 161)

      <?xml version="1.0" encoding="utf-8"?>
      <service>
      <short>SNMP</short>
      <description>SNMP protocol</description>
      <port protocol="udp" port="161"/>
      </service>

   2. Reload your firewall for checking any error

      firewall-cmd --reload

   3. Add the service to your public zone

      firewall-cmd --zone=public --add-service snmp --permanent

   4. Reload your firewall again

      firewall-cmd --reload

Now Test Snmp Status from another server

snmpwalk -v 2c -c public IP.of.target.server

Block scraper bots nginx

 

For those not using wordpress at all and just want to block annoying scraper bots:

location ~* /wp- {
    deny all;
}

or better yet:

location ~* /wp- {
    return 302 https://www.youtube.com/watch?v=dQw4w9WgXcQ;
} 

source:https://gist.github.com/nfsarmento/57db5abba08b315b67f174cd178bea88

Blocking access by user agent in Nginx

 

How to block access by user agent in Nginx. In this configuration, i will use ngx_http_map_module.

Inside http section:

include /etc/nginx/blacklist;

Inside server section (virtual host). We will return 444 status code.

if ($block_ua) {
        return 444;
}

The blacklist file (example)

map $http_user_agent $block_ua {
        default           0;
        ~*profound        1;
        ~*scrapyproject   1;
        ~*netcrawler      1;
        ~*nmap            1;
	~*sqlmap	  1;
	~*slowhttptest	  1;
	~*nikto		  1;
	~*jersey	  1;
	~*brandwatch	  1;
	~*magpie-crawler  1;
	~*mechanize	  1;
	~*python-requests 1;
	~*redback	  1;
}

For testing:

aelius@macbook:~$ curl --head -A "profound" https://www.unixteacher.org/
curl: (52) Empty reply from server

What is http status 444 ?

A non-standard status code used to instruct nginx to close the connection without sending a response to the client, most commonly used to deny malicious or malformed requests.