The Effects of Latency on Throughput

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 reading

Packet Capture Capabilities of Cisco Routers and Switches (Mind Map)

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

The best way to learn…

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!

Books + Books

And remember:

“Knowledge is nothing unless shared and put into practice”

Network Collective #6 – What I Wish I Had Known

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

Running Cisco UCS Platform Emulator on VirtualBox

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

BGP Large Communities: RFC 8092

Well… seems I have been sleeping for a while. Draft BGP Large Communities about which I wrote a little while ago here already go to it’s final stage about a month ago. RFC 8092 was published mid February/2017.

Looking at the differences between draft 06 (published October/2016) and RFC 8092 little was changed except for small language corrections and the “Reserved Large BGP Community values” section.

Will you be able to play with Cisco routers? Not yet! The “big ones” like Cisco and Juniper have not implemented any draft or the RFC. But if you want to stay updated please keep looking at the implementations page. IXPs (Internet Exchange Point) thatfrequently use servers running opensource routing software can already upgrade their code and start testing and defining policies and community values. This Internet Draft is a good start.

To better understand what this new BGP attribute is, have a look at my post from 2016: Large BGP Communities (Internet Draft).

The end of “classic” IOS

If you’ve been in IT and networking in the last 5 years, you definitely know the 1st family of Cisco ISR (Integrated Service Routers) 1800, 2800 and 3800. If that’s true, you also seen the transition to ISR G2 (1900, 2900 and 3900) and felt the frustration of the new licensing model.

Well, last month, the end of ISR G2 was also announced and the recommended platform to migrate to in this range are the 4000 ISR.

7600 routers, the old school warriors also had their End-of-Sale announcement and the replacement should be the ASR 9000.

What does this have to do with the title?

Lately (15 years?) Cisco has been introducing new routers working with new operating systems:

  • ASR 1000 running IOS XE in the enterprise edge and aggregation
  • ASR 9000 running IOS XR in the Service Provider core and edge
  • Nexus switches running NX-OS in the Data Center

All of these new OS’s are modular and bring only advantages when compared to the old IOS (Internetwork Operating System).

ISR 4000’s are no longer running IOS but IOS XE. ASR 9000 – recommended for the replacement of 7600’s – runs IOS XR. 2960 and 4500 switches have left IOS and have been running IOS XR for some years now.

This trend clearly shows us that the well known “classic” and monolithic IOS we came to love and hate since the 90’s is coming to an end. After these announcements, there are very few that still run “pure” IOS.

Is there a reason to worry?

No. Fortunately, NX-OS and especially IOS XE is keeping syntax and CLI (Command Line Interface) similarities with the original IOS. The notable differences are underneath in software architecture (Linux Kernel), modularity, memory protection and high availability. Only IOS XR has big differences but you can get the hang of it quickly with a few month’s practice (have a look at XRv)

You want to know a bit more?

Difference between IOS, IOS XE and IOS XR

Cisco NX-OS

Cisco ASR 1000 Series Aggregation Services Routers Software Configuration Guide: Software Packaging and Architecture

2900 End-of-Sale Announcement

3900 End-of-Sale Announcement