AlexJ's Computer Science Journal

Category Archives: Tech Stuff

LinuxCon Europe 2015 – On stage (part 2)

[Article is part of the series on LinuxCon Europe 2015] The evening of the first days contained another set of keynotes. They started with the Kernel Developer Panel. Aside from the chat with Linus, this is the most interesting part of the LinuxCon, in my opinion. The panel is formed of a couple of kernel […]

State of Mobile Operating Systems

… and thoughts about their future. When we think of Mobile Operating Systems we mostly think of Android and iOS which have the vast majority of the market share. I am a big (openly) Android fan for many reasons. Though it’s not perfect (for example, I would like the development model to be a little […]

K, kilo, kibi, bytes, bits and the rest

While writing the previous article, I had again to deal with the confusion caused by the question “What is a KB?”. Let’s start with some well known facts. First, unless you live in the US (and Myanmar and Liberia), you use the metric system. This means that you have some basic units, like meter, second, […]

DevConf 2015 – Part 1: Introduction

This weekend I attended DevConf 2015. It was probably the first time I went to a conference that I didn’t plan on joining (or didn’t even know about) a month earlier. But since I was in town and I had a free weekend, I went and can’t say that I regret going, because there were […]

Tribute to my Chromebook

Today, something that doesn’t usually happen to me, happened: I broke an electronic. More specifically, my Chromebook fell from a high surface and the screen was damaged beyond repair. So I thought that, as I say farewell to this great piece for hardware, I would publish the reasons why I think the it is awesome. […]

VPS Security

I recently decided to migrate this site from an older server to a VPS. I went with IntoVPS because I got some positive feedback from people I know and use their services. Although I am a big user of Ubuntu Server(LTS), I went with a CentOS install. My first Linux interactions were with RedHat based […]

Online Education: YouTube Education (again)

I imagined I was going to end this series a while back, but it seems that I keep finding related topics. I already discussed this particular topic before and I am just going to make some amendments. Recently, I keep running into some amazing science channels on YouTube. And what’s interesting is that these channels […]

LinuxCon Europe 2013 – part 3

The third day of LinuxCon Europe was, probably, the most awaited because of the star guest: Linus Torvalds. The father of Linux sat down for the morning keynote answering questions from the moderator and the public. Video online. First question was about what makes a good Linux kernel maintainer. And he answered very nice and […]

LinuxCon Europe 2013 – part 1

A couple of weeks ago, I was in Edinburgh, Scotland (UK) for the 2013 European edition of LinuxCon. It was my first time at LinuxCon and it was the biggest conference I attended (it’s bigger and nicer than FOSDEM). And I got to visit a very nice city: Edinburgh. If you ever get the chance […]

Open Source Software on Windows

I use Windows 7 on my laptop. But that doesn’t mean that in the Windows world you can’t find OSS. So I would like to make a list of the programs that I install on my machine when I do a fresh install of the operating system. And for those who didn’t know that there […]

[Techblog] Grub2 and ISO boot

[Originally posted on ROSEdu Techblog]   Grub2 is the next generation Linux bootloader that is trying to replace the “Legacy” Grub version. It is a complete rewrite of Grub 1 and only lately becoming fully featured compared to the old version and even comes with some new interesting features. The old Grub’s configuration was rather […]

[TechBlog] Exploiting environment variables

[Part 1 from ROSEdu Techblog] Environment variables are sometimes very important when creating new processes. For example, the PATH variable, that decides what executable to run. The easiest example to exploit PATH is to add the current directory . to the list and overwrite common shell commands with something else. $ cat ./ls echo P0wn3d […]

[TechBlog] ifconfig vs iproute2

[Originally posted on] On modern Linux distributions, the users have two main possibilities of configuring the network: ifconfig and ip. The ifconfig tool is part of the net-tools package along side other tools like route, arp and netstat. These are the traditional userspace tools for network configuration, made for older Linux kernels. The iproute2 […]

[CCIELab] IOS + Linux = Quagga

[Originally posted on] Cisco IOS’s shell is a popular interface for devices in the networking world. But also in the network world, there are a lot of Linux/Open Source fans. The Quagga open source project tries to bring together IOS and Linux, by providing an IOS-like interface for configuring Linux’s interfaces, routing table and […]

[TechBlog] Stack Allocation

[Originally posted on] Stack space is the part of each process’ virtual memory where function arguments and return addresses are stored, along with local variables declared within a function. Usually, the stack begins at the high address space of the virtual memory and grows down. At every function call, a new stack frame is […]

[CCIELab] Output manipulation in Cisco IOS

[Originally posted on] Unlike Linux’s iptables, Cisco’s filtering via Access Control Lists sometimes has hidden behavior. Let us test how ACL filtering works using the following topology. We assume that we have Layer 3 connectivity via static routes. We will apply ACLs on the outbound direction of F1/0 on R2 (we want it to […]

ROSEdu Tech Blog

This fall, ROSEdu[1] introduced a new project: TechBlog [2]. Since we managed to gather a lot of technical-oriented in our  community, each having things to say about different technologies, we built a place where to share such knowledge in the form of a blog. Here is my first contribution. Rescuing executable code from a process […]

RIP lab: Send RIP routes to remote neighbours

[Originally posted on] Scenario: You have two routers running RIP, but the two routers aren’t directly connected because there is a third router between them. See topology below. How do you get routes across because RIP only communicates with routers that are directly connected? The simple answer is to create a GRE tunnel between […]

Private Networks – Introduction and Legacy Solutions

META: This article is a draft for a chapter of my Research Paper for this semester. Introduction An Enterprise Network is usually a network of a medium-to-large company that has multiple branches in different geographical locations, each branch with its own local data networks. The branches need to communicate in order to access each other’s […]

[CCIELab] Frame Relay Switching

[Originally posted on] Frame Relay is still very much a popular subject in exams, labs and in the real networks. Any lab with topologies that run different protocols over FR must start with the layer 2 configuration of the Frame Relay switched network. FR Topologies like full mesh or hub and spoke require a […]

[CCIELab] Back-to-back Frame Relay

[Originally posted on] This is the simplest use of a Frame Relay encapsulation and it’s between two routers, without a Frame Relay Switch. PPP or HDLC would make more sense to use in these types of links, but it is useful in labs. In a back-to-back scenario is important to remember what the FR […]

[CCIELab] Output manipulation in Cisco IOS

[Originally posted on] One of the things that make Command Line Interfaces, like Bash, very efficient for administration is the output manipulation with piping and redirecting. Cisco IOS has most of the Bash equivalent modifiers, and administrators that know how to work with them can do things much more faster… this can make the […]

Academy War Games. ROSEdu Tech Talks

Astăzi, 10 octombrie, au avut loc două evinimente în facultate. La ora 14 a fost prima prezentare din cadru ROSEdu Tech Talks. Prezentarea a fost ținută de Răzvan Deaconescu, care a prezentat Preprocesorul C. La acestă primă sesiune au participat apoximativ 20 de studenți. Prezentarea este publicată pe pagina proiectului [1] și înregistrarea video urmează […]

Juniper Certified Associate in Enterprise Routing

Am reușit vineri să iau examenul JN0-342, ceea e mă face un Juniper Networks Certified Internet Associate in Enterprise Routing. Deci concluzia experimentului [1], este că se poate trece un examen de certificare de nivel entry level fără să ai experiență practică cu echipamentele firmei respective, lucru care este destul de trist pentru că înseamnă […]

IPv6 Part III: Linux Routing

[Part I] [Part II] Clientul este un Linux box. Legătura la Internet este prin eth1, interfață peste care se face tunelul 6to4. După ce am creat tunelul, am aflat că pot cere o clasă de IPv6 să fie routată prin IP-ul meu v6. Astfel, mi-a fost alocată rețeaua 2001:470:9f00::/48 ( 1208925819614629174706178 adrese adică adică aproximativ […]

IPv6 Part II: Linux Configuration

[Part I] De la provider-ul tunelului [1] am primit următoarele: Server IPv4 address: Server IPv6 address:     2001:470:1f0a:68d::1/64 Client IPv4 address: Client IPv6 address:     2001:470:1f0a:68d::2/64 Între cele două adrese IPv4 este creat un tunel ce are alocată rețeaua IPv6 2001:470:1f0a:68d::/64 ( deci aproximativ 18 milidarde de miliarde de adrese pierdute pentru 2 adrese…dar nu […]

IPv6 Part I: TunnelBroker & IPv6 Certification

Deși mai configurasem o adresăIPv6 și cu alte ocazii [1], nu intrasem adânc în subiect decât la clasa de BSCI de la Cisco pe care am terminat-o recent. După clasă, pentru că mi-a plăcut subiectul, am încercat să văd IPv6 în viața reală, ceea ce era puțin problematic pentru că legăturile mele la Internet vin […]

Security boost in Wireless with VPN

Când ai un laptop, ești foarte fericit când găsești o conexiune Wireless pentru a te conecta la Internet. Problema este că, de obicei, rețele publice sunt Open, adică nu au nici o securitate în transferul de date. Majoritatea software-ului  nu trimite encriptate datele și este foarte ușor ca cineva să captureze parole sau conversații. O […]

Diacritice(UTF-8) & JDBC/mySQL/HTML

Ce am dorit să fac: un program în Java ce capturează conversații de pe IRC și le stochează într-o bază de date mySQL; din acea bază de date se ia prin PHP și se afișează pe o pagină HTML. Deși pare destul de mult de făcut, necesită puțin cod, dar multă atenție la interconectarea elementlor: […]

Cisco VoIP quick HOWTO

Una din direcţiile majore de dezvoltare a Cisco este Voice over IP. Cisco oferă un număr mare de echipamente, software şi soluţii pentru VoIP. Soluţiile VoIP se conectrează în jurul a Cisco Call Manager care este un Call Agent. Este un software ce face administrarea reţelei de VoIP. Acest software vine în două variante: Cisco […]

OpenVZ Full HOWTO – Part I: Basic Install

Am mai discutat despre OpenVZ [1] iar în continuare voi prezenta un deployment simplu. Pornim de la o maşină VMware (în cazut unei instalări reale, în locul mașinii VMware am avea o stație fizică) în care avem instalat un Debian Lenny (basic install). Acesta va fi serverul OpenVZ cu numele de hostname Cronus. Instalăm pe […]

Cisco Switching Case Study: VLANs & VTP

Iată o problemă ce nu prea este documentată dar cu care, dacă lucraţi cu switch-uri cu management, foarte probabil o veţi întâlni. Topologie: Trei switch-uri Catalyst legate între ele în linie şi două hosturi ataşate la capete. Situaţie: În primul rând avem între switch-uri legături trunk şi, important, nu rulează VTP (switchurile sunt în transparent […]

Home Routers: GNS3 & IPv6

Termenul de care aud mult prea des in ultimul timp este IPv6. Don’t get me wrong, sunt pro IPv6, doar ca nu imi place ca se vorbeste prea mult si se implementeaza prea putin. In curiculumul nou de CCNA4 exista o buna bucata de IPv6 (desi calitatea lui lasa de dorit, precum si lipsa laboratoarelor […]

Cisco Expo 2008 – day 2

Day two… am venit direct la prezentari. In ziua 2, in orice moment al zilei aveai de ales intre 5 prezentari (cate una pe sala). Prima data am mers la prezentarea despre Istoria IP Telephony tinuta de Kernel Control (mi-am adus aminte ca ei au avut o prezentare frumoasa la Cisco’s NetReady 2007). Continutul prezentarii […]

Cisco Expo 2008 – day 1

Prezent de la prima ora acolo, cum am ajuns in sala am avut de rezolvat problema IP-urilor de la standuri (daca cu o zi inainte echipa de networking rezolvase Layer1, azi am finalizat si Layer3) All ok in the end si am incercat sa prind ceva din expozitie ca participant. Prima zi a inceput de […]

Guide to Remote Admin Tools

Multe din taskurile unui sysadmin nu se fac de pe tastatura conectata la masina respectiva. Deci administrarea de la distanta a sistemelor este un skill important. Am sa trec in revista cateva tool-uri pe care eu le folosesc. Primul protocol la care ma gandesc cand vine vorba de subiectul acesta, este telnet, dar practic asaceva […]

Firefox Add-ons

Firefox… no introduction required (si daca nu ai auzit de el, probabil ai gresit site-ul 😛 ). Dupa lungi asteptari, Firefox3 a fost scos acum ceva luni. Ziua in care a fost scos a fost numita Download Day 2008, zi in care s-a stabilit recordul mondial pentru cele mai multe download-uri a unui soft in […]

Linux-Windows Dual boot: worst case scenario

Problema de dual boot este ceva destul de intalnit in ultima vreme. Vrei sa tii si Linux si Windows (sau orice alt sistem de operare) pe aceeasi masina. Se rezova foarte usor prin instalarea mai intai a Windows-ului si apoi a distributiei de Linux care vine cu GRUB (care se instaleaza frumos si automat in […]

LHC:power on

Dupa asteptari lungi, azi, 10 septembrie 2008, a fost pornit LHC (the Large Hadron Collider ). Este considerat cel mai mare experiment stiitific din istoria umana. Este un complex construit sub pamant, la granita intre Franta si Elvetia, ce consta intr-un tunel circular de 27km lungime avand ca scop accelerarea particulelor pana la 99.999999% din […]

XMPP Howto

Partea a doua a discutiei despre XMMP este un tutorial despre cum putem pune in practica sistemul. La fel ca o infrastuctura de VoIP avem nevoie de unul sau mai multe servere interconectate si mai multi clienti care se conecteaza la unul din servere (dupa o autentificare). Pagina de la care am pornit a fost […]

Instant Messaging: XMPP

Comunicarea pe Internet si-a schimbat multe forme de-a lungul lungul timpului. Pornind de la email si newsgroups, la forumuri si IRC si ajungand la metode cat mai apropiate de real-time si cu cat mai multe facilitati: instant messanging (tendinta fiind spre comunicarea in lumi virtuale, gen SeccondLife). Cea mai cunoscuta forma este acum Yahoo Messenger […]

Home Routers: Dynagen tips & tricks

Continuare la introul despre Dynagen si Dynamips, as vrea sa prezint niste feature-uri din acestea. Accesul la routerele emulate se face prin telnet. By default, clinetul este telnet-ul din Windows sau Linux (care in cazul Windows sucks…parerea mea…si asta daca el este instalat, a se vedea Vista). Eu prefer sa folosesc Putty in loc de […]

VMware tips: network interfaces

VMware este un soft foarte util pentru un student la calculatoare si in general pentru cineva care vrea sa descopere lumea sistemelor de operare. Ca pasionat de retelistica, mi-a placut in mod special optiunile de interactiune cu reteaua. By default, VMware (Workstation) ofera doua conexiuni cu sistemul de operare gazda: bridged sau NAT (aceste conexiuni […]