Back to GIT! Just to have a quick recap of the things we’ve seen in the first part of our GIT deep dive, I am going to create a brand new repo, some files and commit everything:
$ mkdir myrepo2
$ cd myrepo2
$ git init
Initialized empty Git repository in /Users/huidesa/myrepo2/.git/
$ touch file1
$ touch license_agreement
$ touch installer.exe
$ touch hello.lib
$ git status
On branch master
(use “git add <file>…” to include in what will be committed)
nothing added to commit but untracked files present (use “git add” to track)
$ git add *
$ git status
On branch master
Changes to be committed:
(use “git rm –cached <file>…” to unstage)
new file: file1
new file: hello.lib
new file: installer.exe
new file: license_agreement
$ git commit -m “Creating my project”
[master (root-commit) ac129d8] Creating my project
Committer: Alexandra <[email protected]>
Your name and email address were configured automatically based
on your username and hostname. Please check that they are accurate.
You can suppress this message by setting them explicitly. Run the
GIT is a distributed VCS (Version Control System). In a few words, this means that is a system that allows you to keep track of changes made to a file. The files are stored on a server and each contributor has a local copy of them. Most of the times it’s used when dealing with software development environments, because there is usually a team that works on the same set of files. If it weren’t for GIT (or any other similar tool) everyone would probably overwrite changes that everyone else did to the code and madness would break loose. Still, if you’re not a code developer, you can use GIT to help you keep track of your own files, changes, etc. and keep your head clean!
First time I ran into GIT I had absolutely no idea what it was. For some time, until I had the time to ding into it, I had a note with commands and “what does it do” for each command. This is a “don’t do it like this”-like story. Most definitely, it’s a mistake to take this path because you’ll get to the point where you’ll screw things up so badly Continue reading
IS-IS Subnetwork Independent Operation
Continuing our journey through the land of IS-IS and hoping to reach the point where we get to understand how it actually works and the differences between it and OSPF, let’s focus today on how IS-IS is configured and why it uses both Levels and Areas.
So far, we’ve got some things cleared, as to where that odd node addressing scheme for the routers comes from, what is CLNS and CLNP and a few words on the hierarchy that IS-IS employs. To further things out, let’s go a bit deeper into the structure of the protocol itself.
The thing with IS-IS is that is Network layer independent, though the first thing we tend to do when configuring it is jump to the IP addressing. Consequently, today we’ll see how the OSI IS-IS works without configuring a single IP address, and then if we get to understand this, we can move on to the Integrated IS-IS operation
From a really high level, IS-IS operates as follows:
After getting familiar with the FA, when it’s set and when not, we’re ready to cook the recipe for chaos: NSSAs, Default Route injection and Forwarding Address.
Probably a good disclaimer for this article is – I agree, usually there are other, more simple and straightforward solutions to doing what I did, but in cases where you know 3 solutions to a problem, and none can be applied, it’s good to have the 4th one a click away.
To begin with, the network design we’re going to be experimenting on today is not extremely common, but has a practical application though.
I will start by not sharing the configuration files for this design, with a simple reason – Please lab it yourselves! You will have all sorts of things to gain from this, from typing rapidity, thinking the addressing scheme to troubleshooting your own mistakes. It’s not that big of a deal and it should not take you more than half an hour.
On a high level overview, everything you need to know is on the scheme. Nevertheless, here are the configuration principles:
Everything old is new again. That applies to most industries, trends and businesses, so why wouldn’t it apply to how we use resources and where they are placed.
A history lesson
In the 1970’s, IBM developed the first time sharing service implementation via virtual machines and the VM OS.
A few years back, everyone was building data centers.
Then, computing power and data storage were moved to a place everyone called “Cloud” but no one actually knew what it was and that in fact represented a new name for an old dream Douglas Parkhill was writing about it in 1966 in “The Challenge of Computer Utility”. The term became popular starting 2006, when Amazon launched its EC2 (Elastic Cloud Compute) service. In 2008, Microsoft followed the footsteps and launched Azure, their own Cloud service and in 2013 IBM announced the acquisition of SoftLayer, forming the IBM Cloud Services Division.
IoT is the new hit
Now, there’s the mighty Internet of Things, which promises to connect everything, but brings us back at least to the partial decentralization of resources and leads the way for the so called “Fog”. IoT is estimated to connect approximately 50 billion devices by 2020, according to Continue reading
The theme question is actually quite a good one, because it may seem like the fight has already been won by IS-IS in the Service Provider segment, and by OSPF on the enterprise market. So why ask it then? Well, because I got the following answer one too many times: “IS-IS is awesome, OSPF not so much. I have no idea how IS-IS works but it’s great. OSPF is so complicated and offers so little flexibility…”.
Well, that’s really wrong from my point of view. No protocol can be neither awesome nor despicable. They both offer you advantages and disadvantages, and knowing how they both work will help you make the best decision based on the needs of the network, not just because people say one is “great” and the other is not.
So, I am going to follow the steps I took to come to terms with IS-IS, and then we’ll see together, even though you’ll probably figure it out for yourselves by then, the comparative analysis of the two IGPs.
Step 1: Understanding CLNS & CLNP
Often network engineers freak out when they hear about the OSI stack, CLNP (Connectionless Network Protocol) and CLNS (Connectionless Network Service). Continue reading
Getting to the point where big is never big enough, one may think “What’s cooking?” Well, BGP in the DC is a subject that’s been under my radar for some time, so the purpose of this article is to get things a bit more straight-forward regarding the WHYs and HOWs.
A look in the past
First of all, we should ask ourselves who was Clos. Charles Clos started his work at Bell Labs, mainly focusing on finding a way to switch telephone calls in a scalable and cost-effective way. In 1953, he published the paper “A Study of Non-Blocking Switching Networks”, where he described how to use equipment having multiple stages of interconnections to switch calls.
The crossbar switches (you may think of them as common use switches with a defined number of ports) connected in a three-stage network (ingress, middle, egress) form the so called Clos network.
This had a pretty big use back in the 1950’s but once the level of circuit integration got to the point where interconnections would no longer be a problem, it was no longer of interest, at least for some time. Until huge scale data centers came to be needed (and Continue reading
Hoping you all enjoyed the first part of the OSPF forwarding address saga, I’m back with the promise to make things clear regarding a nicely built redistribution case. I’m not sure if you’ve ever come across it, or ever will, but it’s interesting because it explains why we need the rules to set the forward address (if you don’t remember them, you can take a look at Part I).
Let’s see what I’m talking about. Remember the second topology from Part I? Long story short, I tried to break it. Managed to partially do it, though I am still thinking of a way to make things worse, if possible :). The following setup consists in the starting point of Part II:
Initially, R2’s and R3’s interfaces towards R0 are included in area 0, in order for them to fulfill all the conditions to set the forwarding address in their T5 LSA. The snippets below show the initial state:
R1#show ip ospf interface brief
Interface PID Area IP Address/Mask Cost State Nbrs F/C
Fa1/0 1 0 10.10.13.1/24 1 DR 1/1
Fa0/0 1 0 10.10.12.1/24 1 DR 1/1
R2#show ip ospf Continue reading
OSPF (Open Shortest Path First) is mostly seen as a pretty nasty routing protocol, with a load of subtleties and corner cases. I’ve decided to talk about a subject which usually gives a lot of troubles to most network professionals – the Forwarding Address (FA).
So, we’re going to clear things on why does OSPF set or doesn’t set the FA, what is it used for, how is the best path selection is influenced by the setting of the FA and we’ll also see some examples that may throw some light on this subject. But first, let’s clarify what the forward address is. As per the RFC, the forward address is defined as:
Forwarding address Data traffic for the advertised destination will be forwarded to this address. If the Forwarding address is set to 0.0.0.0, data traffic will be forwarded instead to the LSA's originator (i.e., the responsible AS boundary router).
Probably the most important thing when you start the deep dive into this subject is having the right topology to work with, which allows you to see the less usual cases regarding how redistribution into OSPF works.
Considering the network topology below, I have Continue reading
About 4 years ago, Harald Haas, a physicist and professor of mobile communications at the University of Edinburgh, was the first to coin the term Li-Fi, at a TED Talk during TEDGlobal 2011. Since then, millions of bits about this technology roamed the Internet, and many companies already started implementing it.
Who’s doing this already?
The history begins with a company named Velmenni, which has produced a light bulb that works with Li-Fi technology on a small scale. They are not the first to prove the technology works, nor the first to conduct a real-world experiment, but here’s their Jugnu Lighbulb demo.
Philips has developed a VLC (Visible Light Communication) system for shoppers at stores. People have to download an app on their smartphone and then it will interact with the LEDs in the store. The LEDs can pinpoint their location in the store and give them corresponding coupons and information based on which aisle they are on and what they are looking at.ByteLight has developed a system similar to Philips’ lighting network, making LEDs “talk” to any smartphone and tablet with a camera and/or Bluetooth Smart technology that is “opened to listen”.
The first VLC smartphone prototype was Continue reading
After a pretty long time no write, the big day came, when I decided to revive a project most dear to me.
For those of you who remember n3topedia, and for those of you who’ve never heard of it, a purpose statement may be worthy at this point. From a strictly educational blog, n3topedia will be transformed in a tech blog.
I am pretty certain that networking posts will be an important part of this, but my focus will also be on letting you know whatever feels interesting and useful. Both the format and the approach will be slightly different, more lively and interactive.
I am hoping you will all enjoy reading it as much as I enjoy writing it.