My Linux

Packet sniffing/capturing is a troubleshooting tool that many system and network engineers use for troubleshooting. If you're like me who uses Linux a lot, tcpdump is a useful tool that you can use. In this tutorial, I'm listing a couple of frequently used tcpdump commands  that I use. I'll keep adding additional interesting commands that I stumble upon over time. Installing tcpdump CentOS/RHEL # yum install tcpdump Ubuntu/Debian # apt-get install tcpdump Examples tcpdump requires root privileges. Please use a privileged user, or use sudo  where applicable. Running tcpdump and listening on all network interfaces # tcpdump Listening on a specific network interface # tcpdump -i eth0 All my examples have  ' -i eth0' parameter because I'm used to it. You could choose not to use this parameter depending on your use case, for example if you have only one NIC in the server. Write packet capture to Wireshark compatible...

DNS-based Blackhole List (DNSBL) or Real-time Blackhole List (RBL) is an effort to fight spam emails. It is a blacklist of source IP addresses that have a reputation of sending spam emails. Most email systems can be configured to check these lists and block or flag emails that were sent from domains/IPs listed there. The ‘Blackhole List’ is sometimes called ‘blacklist’ by email admins. In this tutorial, we’ll see how we can configure RBL with Zimbra using both GUI and CLI. Method 1 - GUI: Login to the Zimbra admin console – https://mail.example.com:7071 , and then go to Configure . Configure Then, go to Global Settings . Global Settings Next, go to MTA . I’ve enabled some parameters to harden the server, and added the RBLs that Zimbra supports. You could add the RBLs of your choice here. MTA Changes   Save your settings. There no need to do any service restarts. Zimbra...