Articles tagged with #Linux




You need no MX record to get mails

That one is funny. One client of ours that is actually themselves provide ISP services in a far-far-away land asked to add PTR record for their mail server . But that was dull, the interesting part was that their domain had absolutely NO MX record ! Only A record for the mail …



Skynet got blacklisted - Google mail servers entered RBL of Sorbs.net

When yesterday my client sent me the headers of blocked by eSafe (Aladdin) mails I was quite surprised - the message said " Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this …



Query non-standard port of SNMP with snmpwalk

Sometimes the simple things are the ones to perplex us the most . Today I needed to add an SNMP monitoring of the Radware Linkproof load balancer listening on the port 7777 . Not a big deal, I thought. But before doing it in the monitoring system I wanted to be sure …



MAC finder script

While I don't like going down to Layer 2 , recently I had to do it - I didn't know IP address of the Cisco router I wanted to connect to but I had access to the Cisco router sitting in the same network. That would be pretty easy to do #show …



How to choose the password that noone can guess and you cant remember

Of course you know what the good password should be - random letters including capitals, peppered with numbers and enhanced with printable control characters. The only problem with these recommendations is that there are very few people in the world that can memorize such incomprehensible sequence of chars. So if someone …



Top 10 usernames used in SSH brute force

As a follow up to yesterday's post I thought it would be interesting to know statistics of the usernames used in those brute force probes. Find below awk/sed script to get usernames for failed ssh login attempts from OpenSSH daemon and sort it for statistics. Also I attach the …



SSH brute force is on the rise, awk script to count failed SSH attempts

SSH brute forcing is still in high demand. I have , for my own testing and pleasure, virtual servers scattered around the world. All of them being of the Linux/BSD family I manage by SSH. Also I have on purpose no static IP at home for various reasons (saving me …



Alert on change of SOA in domain

This comes from unpleasant experience of mine. One of my clients’ domain records (MX for the case involved) was mistakenly changed. While it was a human error and trying to fix humans is rolling the rock of Sisyphus,damage would be much lesser had I known about the change immediately …



SSH login alert by mail Linux or Unix based systems

You can get mail lerts on SSH login to any Linux server using the script below. This script sends mail to predefined email address each time someone successfully logs in by SSH to the machine. I take advantage here of the built-in feature of the OpenSSH daemon – if you create …



Ping – setting don't fragment bit in Linux/FreeBSD/Solaris/Cisco/Juniper

Ping. Many times while debugging network problems of various kinds you need to send some packets of desirable size and don’t fragment bit being set. I list below how to do it for the different equipment/OSes. Let’s start with the most popular operating system among network folks …