Studying packet captures is one of the best methods to learn the operation of protocols in any of the 7 network layers. It doesn’t matter if they were made in wireshark, tshark, tcpdump or any other program.
Thanks to the work of very good people we do not need to create the conditions ourselves and make these captures. There are several “capture banks” available for us to enjoy and learn from:
Some people asked me (… well, only one person) how was it possible to add latency between hosts in one of my previous articles about the effects of latency on throughput. When I decided to write the article, my searches led me to tc: Adding Simulated Network Latency To Your Linux Server. Of the different options available, this looked like the best one since there was no need to use a middlebox between the hosts.
How does it work? Continue reading
This weekend I found an interesting RFC (Request For Comments). “RFC 8900 – IP Fragmentation Considered Fragile“. It was one of the few RFCs I read from start to finish without a professional interests or a certification in mind.
I still remember 2009 when I was assigned the task to validate a satellite internet link with 16Mbps bandwidth. At that time that was a looooot in my country.
My biggest surprise was that no matter how many speedtests and download tests I did, I simply couldn’t reach the full 16Mbps and saturate the link. And there I went to complain with the service provider.
All this happened until a very patient young engineer explained it to me:
Mário, it is a satellite link. Latency is too high, you have to make many simultaneous downloads or use a download accelerator.
And it was there that, for the first time, I learned that high latency links like those satellite links (ping latencies of ~500-600ms) influence not only voice/video real-time communication but it also influences throughput… the “speed”.
Let’s verify that…
Continue readingWeeks ago while working on the @Covid19AO_Stats bot I ran into a problem related to the way Python processes text.
What helped understand what was happening was the presentation below.
For some time I have been trying to learn Python, a programming language that is easy to use and the preferred one for many network engineers taking the first steps on automation. I read some books, watch some youtube videos and create some dumb scripts. But what really helps is creating a project, however small it is and doing it from start to finish. So, I decided to build a twitter bot.
Continue readingAs I was writing another post I realized it’s been a while since a 2 year old could count he number of CCIEs in my country.
Jeriel Atienza and André Malungo were for a long time the only Angolan CCIEs, but today the numbers are quite different.
I do not plan to make this the Angolan version of the CCIE Hall of Fame page but you can find below the current list of Angolan CCIEs that I could find: Continue reading
I recently had a small change in my life which required me to spend more time on the road. It is not the best of places to be and it “eats” a lot of time of our days which could be much more productive.
I am leaving some tips here for app which help not to throw that time away and learn a few things while you are driving.
Have you read the news? No?
Cisco just updated their certification program. The CCNA, CCNP and CCIE certifications. All tracks!
This is the first in a series of posts where I will be doing a brief summary of these changes and try and guide everyone in the middle of their journey to become Cisco certified.
Continue readingIn March 2014 I was a team lead for a small networking team in an Angolan ISP. After 5 years contributing the best I could to get the company of it’s feet, the time was coming for the progression many wished in their professional careers. I was invited to be the head of IT. Niiice!!! Continue reading