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…
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During one of my training sessions someone asked me:
Why is it that none of our providers can give us a ping shorter than 150ms to the “internet”?
And the simple answer is: We can’t beat the physics!!
Let me explain:
From very early in my networking career I have been fascinated by protocol details, packet captures and the features of my top 3 application troubleshooting tool: Wireshark.
Getting the captures on the endpoints (clients/servers) is relatively easy but things can get difficult when you want to capture traffic somewhere in between and is hard to do port mirroring (SPAN) on some remote switch.
Packet Capture Capabilities of Cisco Routers and Switches is an old video (4 years is old right?) posted on the Cisco Support Forums that highlights different methods to get on box packet captures in Wireshark .pcap format or in text output.
The video is an hour long but if you’re in a rush I made it easy for you by summarizing the video in an “easy to read” mind map. grouped by IOS, NX-OS and IOS XR. Continue reading
KRACK is the short name for an attack to the WPA (Wi-Fi Protected Access) security protocol, both WPA1 and WPA2. The vulnerability allows Wi-Fi traffic to be decrypted withouth knowledge of any keys even when using “secure” encryption like WPA2 (personal or enterprise).
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Ever since I was a young man my father always told me:
“The best way for you to learn something is to accept the challenge to teach someone”
Teaching was never on my list of strenghts. I ran away from it the best I could until years ago, where I learned that the above statement was in fact true and I started to lose the fear of public speaking. It is only when you try to teach someone you find out the little details we are still missing.
Recently I started a similar challenge, not because I was asked to, but because I offered myself to strengthen the knowledge on both sides, the one who teaches and the one who learns. Its a “win-win situation”. A “customized training” to a small group of employees about the fundamentals of routing and the OSPF protocol up to CCNP level.
So… It’s now time to find out a bit about what I still know and refresh whatever has already run away.
Back to the basics!
And remember:
“Knowledge is nothing unless shared and put into practice”
I recently came across a podcast called Network Collective which is know into its 6th episode. Of course these days there are millions of podcasts but this one in particular is interesting because it touches on a few points with which I agree.
The topic for this 6th episode was “What I Wish I Had Known” and the conversation is around what guests, with many years of work experience, know now but they wish they would know in the beginning of their careers. Continue reading
My studies of Cisco Data Center technologies have led me to Cisco UCS (Unified Computing Systems). To manage a UCS domain Cisco provides us with the UCS Manager software. This software runs on switch-like devices called Fabric Interconnects acting as the “doorways” between the UCS domain and “the world”.
For all of us studying and needing to understand it without access to a bunch of expensive servers, Cisco was kind enough to create the UCSPE (UCS Platform Emulator) as a free downloadable virtual machine.
Since I’m not a good friend of VMWare and can’t have a bare metal hypervisor, my “playing” focuses mostly on Virtualbox but there is a small detail that must be taken care of:
Problem: After importing the UCSPE appliance you can’t access the GUI even after changing adapter 1 to Host-only or Bridge. Continue reading