Configure Remotely Triggered Black Hole (RTBH) using Blackhole Community to mitigate DDoS

This post is dedicated to Phúc Toàn, a friendly and joyful guy from Ho Chi Minh City, Vietnam. He was  one of the participants in IPv4/IPv6 Routing Workshop at APRICOT 2017. He created his own lab to test RTBH using blackhole community but for some reason it wasn’t working and he showed it to me after the class. We could find the problem, and finally it worked as expected. Later, he took me to a cafe and we had some seasonal fresh... Read more

Generate Cisco IOURC license on GNS3 VM using Python 3

I was trying to add IOU L2 Switch image on GNS3 VM but an wired license error didn’t permit me to start the L2 Switch image. It says: error while starting IOU1: License section not found in iourc file /tmp/tmpkrjoe5hx/iourc Here’s how I solved it. Section 1: Download and add IOU Image on GNS3 VM i) Download Cisco L2/L3 IOU image. Some of them can be found here. You can also Google it to download any specific image. I’m using i86bi-linux-l2-adventerprisek9-15.2d.bin... Read more

Prepare Virtual Lab on Ubuntu Using Dynamips and Dynagen

Dedicated to This post might not be written without the inspiration of Farid Mohammad Rashed Amin aka Biddut-bhai, for whom I have my deepest respect. A tech lover with such an enthusiastic mind at this level just blown my mind. Introduction Routing trainers across the globe wouldn’t be that happier if Christophe Fillot didn’t create an wonderful emulator in 2005 called Dynamips. This application just made our life easier than ever. It’s basically written to simulate some selected Cisco IOS. “Of course, this... Read more

Run Cisco Transport Planner (CTP) on MacOS

Unlike setting up Cisco Transport Controller (CTC) on my MacBook Air, Cisco Transport Planner (CTP) seems much easier to me to run on MacOS. There are actually two ways to do that. One is setting up the CTP installer which I couldn’t run as the installer provided by CISCO was corrupted during the time I was trying it. The other way (and of course the easier one that worked for me) is to run ctp.jar file (a Java based file).... Read more

Install ntopng on CentOS 7 to Monitor Network Traffic

Ntopng, is one of the most popular and powerful open-source network traffic monitoring tools that shows real-time traffic flow and its behaviour in a user friendly and intuitive web interface. The interface has some awesome features like viewing of network traffic, including top hosts data, top flow talkers, application protocols in use, top flow senders data in live mode. I would like to show you how to install ntopng on CentOS 7. Here are the steps: Step 1: Prepare and... Read more

Install and Manage Multiple Versions of Java on OS X

After getting my new job roles of managing the transmission and data network in BdREN, I have run couple of Java based applications like Cisco Transport Controller (CTC), Adaptive Security Device Manager (ASDM), LAN Management System (LMS) etc. It’s wired that most of those applications performs best with different individual Java versions and mostly with older versions like CTC works better on Java 6, ASDM works better on Java 7 and the latest Java version is now 8. After taking... Read more

Fix WordPress ‘Error 406’ or ‘Not Acceptable’

How to fix ‘Error 406 – Not Acceptable’ in WordPress. I have been getting the following error while writing a new blog post. I kept on getting the error message when trying to save a post. Similar problem can appear with different message like: “Error 406, Not Acceptable. An appropriate representation of the requested resource /wp-admin/post.php could not be found on this server” Reason: Error 406 is caused by your webhost and has got nothing to do with you. Most of the... Read more

Setup BGP Looking Glass on CentOS

The organisation where I’m working didn’t have a BGP looking glass (LG). We, network professionals, know how helpful a looking glass is while troubleshooting any network related issues. Hence, I setup my mind to spare a server so that we can run LG there. I installed CentOS 6.5 there. I followed the steps below to setup LG on my CentOS server. Step 1: Download lg-1.9 from GitHub. [root@bdren ~] git clone git://github.com/Cougar/lg.git [root@bdren ~] cd lg [root@bdren lg] ll -rw-r–r–... Read more

Cisco Transport Controller (CTC) installation on MacOS

Installation of Cisco Transport Controller (CTC) was quite easier on my previous Windows 10 laptop than my MacOS Sierra (10.12+). Since, I started using MacOS very recently, it was tricky for me to find a solution to install CTC. Hence, I’d like to write about it here. CTC is a complex java applet ran through a browser that requires access to the $HOME directory of the user. It creates a .ctc directory in the $HOME directory and stores various .jar... Read more

Revoking a PGP key

Using the command line: I use PGP with my emails mostly to sign with digital signature. For some reasons I had to create a new PGP key and revoke my last key (0x43687201) from public key servers like pgp.mit.edu. Key revocation might be necessary for many reasons. Someone might lost his laptop for example. Hence, it’s wise to create a revocation certificate just after the key is generated. I generated it with the following command: $ gpg –gen-revoke 43687201 A revocation key... Read more