Καταγγελία χρηστών για Traffic Shaping απο την Otenet

Μειωμένη απόδοση σε Peer to Peer εφαρμογές έχει παρατηρηθεί το τελευταίο διάστημα σε μερίδα χρήστων οι οποίοι χρησιμοποιούν ADSL συνδέσεις του ΟΤΕ. Το πρόβλημα δείχνει να έχει χαρακτηριστικά Traffic Shaping μέσω Deep Packet Inspection. Αυτό σημαίνει ότι ο ΟΤΕ, πιθανότατα ελέγχει με ειδικό εξοπλισμό τη δικτυακή κίνηση των χρηστών και στη συνέχεια προτεραιοποιεί την κίνηση. Η κίνηση P2P φαίνεται να επιβαρύνεται ιδιαίτερα και άρα συνάγεται ότι λαμβάνει αρκετά χαμηλή προτεραιότητα.

Το πρόβλημα φαίνεται να επηρεάζει διάφορα P2P πρωτόκολλα (Torrents, DC++ κτλ) ενώ εμφανίζεται και σε διάφορες γεωγραφικές περιοχές της Ελλάδας. Το Packet Inspection που χρησιμοποιεταί φαίνεται να είναι ιδιαίτερα αποτελεσματικό αφού πιάνει ακόμα και encrypted κίνηση - η οποία συνήθως "ξεγελάει" το Traffic Shaping. Εξαίρεση αποτελούν μερικοί εξελιγμένοι Torrent Clients των οποίων τo encryption ακόμα δεν είναι ευδιάκριτο από τον έλεγχο των πακέτων. Πιθανότατα αυτό θα αλλάξει στο μέλλον με ανανέωση του λογισμικού Packet Inspection.

Η μειωμένη απόδοση δεν δείχνει να είναι χαρακτηριστική των ADSL συνδέσεων (ΑΡΥΣ) αλλά σχετίζεται με τον λογαριασμό πρόσβασης του παρόχου (ΟΤΕ/ΟΤΕΝΕΤ) αφού με την αλλαγή παρόχου, σε ίδια γραμμή, η απόδοση σε P2P διακίνηση διεξάγεται ομαλά.

Αυτή τη στιγμή διενεργείται συλλογή στοιχείων από όσους αντιμετωπίζουν πρόβλημα, προκειμένου να διερευνηθεί το ζήτημα από την ΕΕΤΤ.


Παρακάτω ακολουθεί video ντοκουμέντο.

Introduction To Network Security

Παρακάτω ακολουθεί ενας συνοπτικός οδηγός για την ασφαλεια του δικτύου μας και πως μπορούμε να προφυλάξουμε τα αρχεία μας από κακόβουλους χρήστες.(σε ατομικό επίπεδο και σε ετερικό επιπεδο).Eπισης ακολουθεί και επεξήγηση στους ορους (penetration-testing,intrusion detection systems, firewall topologies and more)
Αυτά για την ώρα,θα ακολουθήσουν και αλλοι οδηγοί για (ΝΑΤ,PROTOCOLS,DENIAL OF SERVICE ATTACK)read it.....

Introduction

As more and more people and businesses have begun to use computer networks and the Internet, the need for a secure computing environment has never been greater. Right now, information security professionals are in great demand and the importance of the field is growing every day. All the industry leaders have been placing their bets on security in the last few years.

Just recently Bill Gates and Steve Ballmer of Microsoft have been quoted as saying that secure computing is no longer an optional component, it is something that should be integrated into every system rather than being thrown in as an afterthought. Usually programmers would concentrate on getting a program working, and then (if there was time) try and weed out possible security holes.

Now, applications must be coded from the ground up with security in mind, as these applications will be used by people who expect the security and privacy of their data to be maintained.

This article intends to serve as a very brief introduction to information security with an emphasis on networking.

The reasons for this are twofold:

Firstly, in case you did not notice.. this is a networking website,

Secondly, the time a system is most vulnerable is when it is connected to the Internet.

For an understanding of what lies in the following pages, you should have decent knowledge of how the Internet works. You don't need to know the ins and outs of every protocol under the sun, but a basic understanding of network (and obviously computer) fundamentals is essential.

If you're a complete newbie however, do not despair. We would recommend you look under the Networking menu at the top of the site.. there you will find our accolade winning material on pretty much everything in networking.

Hacker or Cracker?

There is a very well worn out arguement against using the incorrect use of the word 'hacker' to denote a computer criminal -- the correct term is a 'cracker' or when referring to people who have automated tools and very little real knowledge, 'script kiddie'. Hackers are actually just very adept programmers (the term came from 'hacking the code' where a programmer would quickly program fixes to problems he faced).

While many feel that this distinction has been lost due to the media portraying hackers as computer criminals, we will stick to the original definitions through these articles more than anything to avoid the inevitable flame mail we will get if we don't !

The Threat to Home Users

Many people underestimate the threat they face when they use the Internet. The prevalent mindset is "who would bother to attack me or my computer?", while this is true -- it may be unlikely that an attacker would individually target you, as to him, you are just one more system on the Internet.

Many script kiddies simply unleash an automated tool that will scan large ranges of IP addresses looking for vulnerable systems, when it finds one, this tool will automatically exploit the vulnerability and take control of this machine.

The script kiddie can later use this vast collection of 'owned' systems to launch a denial of service (DoS) attacks, or just cover his tracks by hopping from one system to another in order to hide his real IP address.

This technique of proxying attacks through many systems is quite common, as it makes it very difficult for law enforcement to back trace the route of the attack, especially if the attacker relays it through systems in different geographic locations.

It is very feasible -- in fact quite likely -- that your machine will be in the target range of such a scan, and if you haven't taken adequate precautions, it will be owned.

The other threat comes from computer worms that have recently been the subject of a lot of media attention. Essentially a worm is just an exploit with a propagation mechanism. It works in a manner similar to how the script kiddie's automated tool works -- it scans ranges of IP addresses, infects vulnerable machines, and then uses those to scan further.

Thus the rate of infection increases geometrically as each infected system starts looking for new victims. In theory a worm could be written with such a refined scanning algorithm, that it could infect 100% of all vulnerable machines within ten minutes. This leaves hardly any time for response.

Another threat comes in the form of viruses, most often these may be propagated by email and use some crude form of social engineering (such as using the subject line "I love you" or "Re: The documents you asked for") to trick people into opening them. No form of network level protection can guard against these attacks.

The effects of the virus may be mundane (simply spreading to people in your address book) to devastating (deleting critical system files). A couple of years ago there was an email virus that emailed confidential documents from the popular Windows "My Documents" folder to everyone in the victims address book.

So while you per se may not be high profile enough to warrant a systematic attack, you are what I like to call a bystander victim.. someone who got attacked simply because you could be attacked, and you were there to be attacked.

As broadband and always-on Internet connections become commonplace, even hackers are targetting the IP ranges where they know they will find cable modem customers. They do this because they know they will find unprotected always-on systems here that can be used as a base for launching other attacks.

The Threat to the Enterprise

Most businesses have conceded that having an Internet presence is critical to keep up with the competition, and most of them have realised the need to secure that online presence.

Gone are the days when firewalls were an option and employees were given unrestricted Internet access. These days most medium sized corporations implement firewalls, content monitoring and intrusion detection systems as part of the basic network infrastructure.

For the enterprise, security is very important -- the threats include:

• Corporate espionage by competitors,
• Attacks from disgruntled ex-employees
• Attacks from outsiders who are looking to obtain private data and steal the company's crown jewels (be it a database of credit cards, information on a new product, financial data, source code to programs, etc.)
• Attacks from outsiders who just want to use your company's resources to store pornography, illegal pirated software, movies and music, so that others can download and your company ends up paying the bandwidth bill and in some countries can be held liable for the copyright violations on movies and music.

As far as securing the enterprise goes, it is not enough to merely install a firewall or intrustion detection system and assume that you are covered against all threats. The company must have a complete security policy and basic training must be imparted to all employees telling them things they should and should not do, as well as who to contact in the event of an incident. Larger companies may even have an incident response or security team to deal specifically with these issues.

One has to understand that security in the enterprise is a 24/7 problem. There is a famous saying, "A chain is only as strong as its weakest link", the same rule applies to security.

After the security measures are put in place, someone has to take the trouble to read the logs, occasionally test the security, follow mailing-lists of the latest vulnerabilities to make sure software and hardware is up-to-date etc. In other words, if your organisation is serious about security, there should be someone who handles security issues.

This person is often a network administrator, but invariably in the chaotic throes of day-to-day administration (yes we all dread user support calls ! :) the security of the organisation gets compromised -- for example, an admin who needs to deliver 10 machines to a new department may not password protect the administrator account, just because it saves him some time and lets him meet a deadline. In short, an organisation is either serious about security issues or does not bother with them at all.

While the notion of 24/7 security may seem paranoid to some people, one has to understand that in a lot of cases a company is not specifically targetted by an attacker. The company's network just happen to be one that the attacker knows how to break into and thus they get targetted. This is often the case in attacks where company ftp or webservers have been used to host illegal material.

The attackers don't care what the company does - they just know that this is a system accessible from the Internet where they can store large amounts of warez (pirated software), music, movies, or pornography. This is actually a much larger problem than most people are aware of because in many cases, the attackers are very good at hiding the illegal data. Its only when the bandwidth bill has to be paid that someone realises that something is amiss.

Common Security Measures

Firewalls:

By far the most common security measure these days is a firewall. A lot of confusion surrounds the concept of a firewall, but it can basically be defined as any perimiter device that permits or denies traffic based on a set of rules configured by the administrator. Thus a firewall may be as simple as a router with access-lists, or as complex as a set of modules distributed through the network controlled from one central location.

The firewall protects everything 'behind' it from everything in front of it. Usually the 'front' of the firewall is its Internet facing side, and the 'behind' is the internal network. The way firewalls are designed to suit different types of networks is called the firewall topology.

Here is a detailed explanation of different firewall topologies :

Introduction

In this section we are going to talk about the different ways a firewall can be set up. Depending on your needs, you can have a very simple firewall setup which will provide enough protection for your personal computer or small network, or you can choose a more complicated setup which will provide more protection and security.

Let's have a look starting from the simple solutions, and then move on to the more complicated ones. Just keep in mind we are not talking about a firewall which is only a piece of software which runs on the same computer you use to connect to the internet and do your work, but we are talking about a physical computer which is a dedicated firewall.

A Simple Dual-Homed Firewall

The dual-homed firewall is one of the simplest and possibly most common way to use a firewall. The Internet comes into the firewall directly via a dial-up modem (like me :) ) or through some other type of connection like an ISDN line or cable modem. You can't have a DMZ (See the DMZ page for more info) in this type of a configuration.

The firewall takes care of passing packets that pass its filtering rules between the internal network and the Internet, and vice versa. It may use IP masquerading and that's all it does. This is known as a dual-homed host. The two "homes" refer to the two networks that the firewall machine is part of - one interface connected to the outside home, and the other connected to the inside home.

This particular setup has the advantage of simplicity and if your Internet connection is via a modem and you have only one IP address, it's what you're probably going to have to live with unless you create a more complex network like the one we are going to talk about.

A Two-Legged Network with a full exposed DMZ

In this more advanced configuration, shown in the picture below, the router that connects to the outside work is connected to a hub (or switch).

Machines that want direct access to the outside world, unfiltered by the firewall, connect to this hub. One of the firewall's network adapters also connects to this hub. The other network adapter connects to the internal hub. Machines that need to be protected by the firewall need to connect to this hub. Any of these hubs could be replaced with switches for added security and speed, and it would be more effective to use a switch for the internal hub.

There are good things about the exposed DMZ configuration. The firewall needs only two network cards. This simplifies the configuration of the firewall. Additionally, if you control the router you have access to a second set of packet-filtering capabilities. Using these, you can give your DMZ some limited protection completely separate from your firewall.

On the other hand, if you don't control the router, your DMZ is totally exposed to the Internet. Hardening a machine enough to live in the DMZ without getting regularly compromised can be tricky.

The exposed DMZ configuration depends on two things: 1) an external router, and 2) multiple IP addresses.

If you connect via PPP (modem dial-up), or you don't control your external router, or you want to masquerade your DMZ, or you have only 1 IP address, you'll need to do something else.There are two straightforward solutions to this, depending on your particular problem.

One solution is to build a second router/firewall. This is useful if you're connecting via PPP. One machine is the exterior router/ firewall (Firewall No.1). This machine is responsible for creating the PPP connection and controls the access to our DMZ zone. The other firewall (Firewall No.2) is a standard dual-homed host just like the one we spoke about at the beginning of the page, and its job is to protect the internal network. This is identical to the situation of a dual homed firewall where your PPP machine is the local exterior router.

The other solution is to create a three-legged firewall, which is what we are going to talk about next.

The Three-legged firewall

This means you need an additional network adapter in your firewall box for your DMZ. The firewall is then configured to route packets between the outside world and the DMZ differently than between the outside world and the internal network. This is a useful configuration, and I have seen many of our customers using it.

The three-legged setup can also give you the ability to have a DMZ if you're stuck with the simple topology outlined first (dual homed firewall). Replace "router" with "modem," and you can see how this is similar to the simple topology (dual homed firewall), but with a third leg stuck on the side :)

If you're being forced or have chosen to IP masquerade, you can masquerade the machine or machines in the DMZ too, while keeping them functionally separate from protected internal machines. People who have cable modems or static PPP connections can use this system to run various servers within a DMZ as well as an entire internal network off a single IP address. It's a very economic solution for small businesses or home offices.

The primary disadvantage to the three-legged firewall is the additional complexity. Access to and from the DMZ and to and from the internal network is controlled by one large set of rules. It's pretty easy to get these rules wrong if you're not careful !

On the other hand, if you don't have any control over the Internet router, you can exert a lot more control over traffic to and from the DMZ this way. It's good to prevent access into the DMZ if you can.

And I think that just about completes our discussion of Firewall Topologies !

You also get what are known as 'personal firewalls' such as Zonealarm
(http://www.zonelabs.com), Sygate Personal Firewall (http://www.sygate.com), Tiny Personal Firewall (http://www.tinysoftware.com) etc.

These are packages that are meant for individual desktops and are fairly easy to use. The first thing they do is make the machine invisible to pings and other network probes. Most of them also let you choose what programs are allowed to access the Internet, therefore you can allow your browser and mail client, but if you see some suspicious program trying to access the network, you can disallow it. This is a form of 'egress filtering' or outbound traffic filtering and provides very good protection against trojan horse programs and worms.

However firewalls are no cure all solution to network security woes. A firewall is only as good as its rule set and there are many ways an attacker can find common misconfigurations and errors in the rules. For example, say the firewall blocks all traffic except traffic originating from port 53 (DNS) so that everyone can resolve names, the attacker could then use this rule to his advantage. By changing the source port of his attack or scan to port 53, the firewall will allow all of his traffic through because it assumes it is DNS traffic.

Bypassing firewalls is a whole study in itself and one which is very interesting especially to those with a passion for networking as it normally involves misusing the way TCP and IP are supposed to work. That said, firewalls today are becoming very sophisticated and a well installed firewall can severely thwart a would-be attackers plans.

It is important to remember the firewall does not look into the data section of the packet, thus if you have a webserver that is vulnerable to a CGI exploit and the firewall is set to allow traffic to it, there is no way the firewall can stop an attacker from attacking the webserver because it does not look at the data inside the packet. This would be the job of an intrusion detection system (covered further on).

Anti-Virus systems:

Everyone is familiar with the desktop version of anti virus packages like Norton Antivirus and Mcafee. The way these operate is fairly simple -- when researchers find a new virus, they figure out some unique characteristic it has (maybe a registry key it creates or a file it replaces) and out of this they write the virus 'signature'.

The whole load of signatures that your antivirus scans for what is known as the virus 'definitions'. This is the reason why keeping your virus definitions up-to-date is very important. Many anti-virus packages have an auto-update feature for you to download the latest definitions. The scanning ability of your software is only as good as the date of your definitions. In the enterprise, it is very common for admins to install anti-virus software on all machines, but there is no policy for regular update of the definitions. This is meaningless protection and serves only to provide a false sense of security.

With the recent spread of email viruses, anti-virus software at the MTA (Mail Transfer Agent , also known as the 'mail server') is becoming increasingly popular. The mail server will automatically scan any email it recieves for viruses and quarantine the infections. The idea is that since all mail passes through the MTA, this is the logical point to scan for viruses. Given that most mail servers have a permanent connection to the Internet, they can regularly download the latest definitions. On the downside, these can be evaded quite simply. If you zip up the infected file or trojan, or encrypt it, the anti-virus system may not be able to scan it.

End users must be taught how to respond to anti virus alerts. This is especially true in the enterprise -- an attacker doesn't need to try and bypass your fortress like firewall if all he has to do is email trojans to a lot of people in the company. It just takes one uninformed user to open the infected package and he will have a backdoor to the internal network.

It is advisable that the IT department gives a brief seminar on how to handle email from untrusted sources and how to deal with attachments. These are very common attack vectors simply because you may harden a computer system as much as you like, but the weak point still remains the user who operates it. As crackers say 'The human is the path of least resistance into the network'.

Intrusion Detection Systems

IDS's have become the 'next big thing' the way firewalls were some time ago. There are bascially two types of Intrusion Detection Systems :

• Host based IDS
• Network based IDS

Host based IDS - These are installed on a particular important machine (usually a server or some important target) and are tasked with making sure that the system state matches a particular set baseline. For example, the popular file-integrity checker Tripwire -- this program is run on the target machine just after it has been installed. It creates a database of file signatures for the system and regularly checks the current system files against their known 'safe' signatures. If a file has been changed, the administrator is alerted. This works very well as most attackers will replace a common system file with a trojaned version to give them backdoor access.

Network based IDS - These are more popular and quite easy to install. Basically they consist of a normal network sniffer running in promiscuous mode (in this mode the network card picks up all traffic even if its not meant for it). The sniffer is attached to a database of known attack signatures and the IDS analyses each packet that it picks up to check for known attacks. For example a common web attack might contain the string '/system32/cmd.exe?' in the URL. The IDS will have a match for this in the database and will alert the administrator.

Newer IDS' support active prevention of attacks - instead of just alerting an administrator, the IDS can dynamically update the firewall rules to disallow traffic from the attacking IP address for some amount of time. Or the IDS can use 'session sniping' to fool both sides of the connection into closing down so that the attack cannot be completed.

Unfortunately IDS systems generate a lot of false positives (a false positive is basically a false alarm, where the IDS sees legitimate traffic and for some reason matches it against an attack pattern) this tempts a lot of administrators into turning them off or even worse -- not bothering to read the logs. This may result in an actual attack being missed.

IDS evasion is also not all that difficult for an experienced attacker. The signature is based on some unique feature of the attack, and so the attacker can modify the attack so that the signature is not matched. For example, the above attack string '/system32/cmd.exe?' could be rewritten in hexadecimal to look something like

'2f%73%79%73%74%65%6d%33%32%2f%63%6d%64%2e%65%78%65%3f'

Which might be totally missed by the IDS. Furthermore, an attacker could split the attack into many packets by fragmenting the packets. This means that each packet would only contain a small part of the attack and the signature would not match. Even if the IDS is able to reassemble fragmented packets, this creates a time overhead and since IDS' have to run at near real-time status, they tend to drop packets while they are processing. IDS evasion is a topic for a paper on its own.

The advantage of a network based IDS is that it is very difficult for an attacker to detect. The IDS itself does not need to generate any traffic, and in fact many of them have a broken TCP/IP stack so they don't have an IP address. Thus the attacker does not know whether the network segment is being monitored or not.

Patching and Updating

It is embarassing and sad that this has to be listed as a security measure. Despite being one of the most effective ways to stop an attack, there is a tremendously laid back attitude to regulary patching systems. There is no excuse for not doing this, and yet the level of patching remains woefully inadequate. Take for example the MSblaster worm that spread havoc recently. The exploit was known almost a month in advance, and a patch had been released, still millions of users and businesses were infected. While admins know that having to patch 500 machines is a laborious task, the way I look at it is I would rather be updating my systems on a regular basis than waiting for disaster to strike and then running around trying to patch and clean up those 500 systems.

For the home user, its a simple matter of running the automatic update software that every worthwhile OS comes with. In the enterprise there is no 'easy' way to patch large numbers of machines, but there are patch deployment mechanisms that take a lot of the burden away. Frankly, it is part of an admin's job to do this, and when a network is horribly fouled up by the latest worm it just means someone, somewhere didn't do his job well enough.

Tools An Attacker Uses

Now that we've concluded a brief introduction to the types of threats faced by both home users and the enterprise, it is time to have a look at some of the tools that attackers use.

Keep in mind that a lot of these tools have legitimate purposes and are very useful to administrators as well. For example I can use a network sniffer to diagnose a low level network problem or I can use it to collect your password. It just depends which shade of hat I choose to wear.

General Network Tools

As surprising as it might sound, some of the most powerful tools especially in the beginning stages of an attack are the regular network tools available with most operating systems. For example and attacker will usually query the 'whois' databases for information on the target. After that he might use 'nslookup' to see if he can transfer the whole contents of their DNS zone (called a zone transfer -- big surprise !!). This will let him identify high profile targets such as webservers, mailservers, dns servers etc. He might also be able to figure what different systems do based on their dns name -- for example sqlserver.victim.com would most likely be a database server. Other important tools include traceroute to map the network and ping to check which hosts are alive. You should make sure your firewall blocks ping requests and traceroute packets.

Exploits

An exploit is a generic term for the code that actually 'exploits' a vulnerability in a system. The exploit can be a script that causes the target machine to crash in a controlled manner (eg: a buffer overflow) or it could be a program that takes advantage of a misconfiguration.

A 0-day exploit is an exploit that is unknown to the security community as a whole. Since most vulnerabilities are patched within 24 hours, 0-day exploits are the ones that the vendor has not yet released a patch for. Attackers keep large collections of exploits for different systems and different services, so when they attack a network, they find a host running a vulnerable version of some service and then use the relevant exploit.

Port Scanners

Most of you will know what portscanners are. Any system that offers TCP or UDP services will have an open port for that service. For example if you're serving up webpages, you'll likely have TCP port 80 open, FTP is TCP port 20/21, Telnet is TCP 23, SNMP is UDP port 161 and so on.

A portscanner scans a host or a range of hosts to determine what ports are open and what service is running on them. This tells the attacker which systems can be attacked.
For example, if I scan a webserver and find that port 80 is running an old webserver -- IIS/4.0, I can target this system with my collection of exploits for IIS 4. Usually the port scanning will be conducted at the start of the attack, to determine which hosts are interesting.

This is when the attacker is still footprinting the network -- feeling his way around to get an idea of what type of services are offered and what Operating Systems are in use etc. One of the best portscanners around is Nmap (http://www.insecure.org/nmap). Nmap runs on just about every operating system is very versatile in how it lets you scan a system and has many features including OS fingerprinting, service version scanning and stealth scanning. Another popular scanner is Superscan (http://www.foundstone.com) which is only for the windows platform.

Network Sniffers

A network sniffer puts the computers NIC (network interface card or LAN card) into 'promiscuous mode'. In this mode, the NIC picks up all the traffic on its subnet regardless of whether it was meant for it or not. Attackers set up sniffers so that they can capture all the network traffic and pull out logins and passwords. The most popular network sniffer is TCPdump as it can be run from the command line -- which is usually the level of access a remote attacker will get. Other popular sniffers are Iris and Ethereal.

When the target network is a switched environment (a network which uses layer 2 switches), a conventional network scanner will not be of any use. For such cases, the switched network sniffer Ettercap (http://ettercap.sourceforge.net) is very popular. It allows the attacker to collect passwords, hijack sessions, modify ongoing connections and kill connections. It can even sniff secured communications like SSL (used for secure webpages) and SSH1 (Secure Shell - a remote access service like telnet, but encrypted).

There are also programs that allow an admin to detect whether any NICs are running in promiscuous mode.

Vulnerability Scanners

A vulnerability scanner is like a portscanner on steroids, once it has identified which services are running, it checks the system against a large database of known vulnerabilities and then prepares a report on what security holes are found. The software can be updated to scan for the latest security holes. These tools are very simple to use unfortunately, so many script kiddies simply point them at a target machine to find out what they can attack. The most popular ones are Retina (http://www.eeye.com), Nessus (http://www.nessus.org) and GFI LanScan (http://www.gfi.com). These are very useful tools for admins as well as they can scan their whole network and get a detailed summary of what holes exist.

Password Crackers

Once an attacker has gained some level of access, he/she usually goes after the password file on the relevant machine. In UNIX like systems this is the /etc/passwd or /etc/shadow file and in Windows it is the SAM database. Once he gets hold of this file, its usually game over, he runs it through a password cracker that will usually guarantee him further access. Running a password cracker against your own password files can be a scary and enlightening experience. L0phtcrack cracked my old password fR7x!5kK after being left on for just one night !

There are essentially two methods of password cracking :

Dictionary Mode - In this mode, the attacker feeds the cracker a word list of common passwords such as 'abc123' or 'password'. The cracker will try each of these passwords and note where it gets a match. This mode is useful when the attacker knows something about the target. Say I know that the passwords for the servers in your business are the names of Greek Gods (yes Chris, that's a shout-out to you ;)) I can find a dictionary list of Greek God names and run it through the password cracker.

Most attackers have a large collection of wordlists. For example when I do penetration testing work, I usually use common password lists, Indian name lists and a couple of customized lists based on what I know about the company (usually data I pick up from their company website). Many people think that adding on a couple of numbers at the start or end of a password (for example 'superman99') makes the password very difficult to crack. This is a myth as most password crackers have the option of adding numbers to the end of words from the wordlist. While it may take the attacker 30 minutes more to crack your password, it does not make it much more secure.

Brute Force Mode - In this mode, the password cracker will try every possible combination for the password. In other words it will try aaaaa, aaaab, aaaac, aaaad etc. this method will crack every possible password -- its just a matter of how long it takes. It can turn up surprising results because of the power of modern computers. A 5-6 character alphanumeric password is crackable within a matter of a few hours or maybe a few days, depending on the speed of the software and machine. Powerful crackers include l0phtcrack for windows passwords and John the Ripper for UNIX style passwords.

For each category, I have listed one or two tools as an example. At the end of this article I will present a more detailed list of tools with descriptions and possible uses.

What is Penetration-Testing ?

Penetration testing is basically when you hire (or perform yourself) security consultants to attack your network the way an attacker would do it, and report the results to you enumerating what holes were found, and how to fix them. It's basically breaking into your own network to see how others would do it.

While many admins like to run quick probes and port scans on their systems, this is not a penetration test -- a penetration tester will use a variety of specialised methods and tools from the underground to attempt to gain access to the network. Depending on what level of testing you have asked for, the tester may even go so far as to call up employees and try to social engineer their passwords out of them (social engineering involves fooling a mark into revealing information they should not reveal).

An example of social engineering could be an attacker pretending to be someone from the IT department and asking a user to reset his password. Penetration testing is probably the only honest way to figure out what security problems your network faces. It can be done by an administrator who is security aware, but it is usually better to pay an outside consultant who will do a more thorough job.

I find there's a lack of worthwhile information online about penetration testing -- nobody really goes about describing a good pen test, and what you should and shouldn't do. So I've hand picked a couple of good papers on the subject and then given you a list of my favourite tools, and the way I like to do things in a pen-test.

This is by no means the only way to do things, it's like subnetting -- everyone has their own method -- this is just a systematic approach that works very well as a set of guidelines. Depending on how much information you are given about the targets as well as what level of testing you're allowed to do, this method can be adapted.

Papers Covering Penetration Testing

I consider the following works essential reading for anyone who is interested in performing pen-tests, whether for yourself or if you're planning a career in security:

'Penetration Testing Methodology - For Fun And Profit' - Efrain Tores and LoNoise, you can google for this paper and find it.

'An Approach To Systematic Network Auditing' - Mixter (http://mixter.void.ru)

'Penetration Testing - The Third Party Hacker' - Jessica Lowery. Boy is this ever a good paper ! (http://www.sans.org/rr/papers/index.php?id=264)

'Penetration Testing - Technical Overview' - Timothy P. Layton Sr. also from the www.sans.org (http://www.sans.org) reading room

Pen-test Setup

I don't like working from laptops unless its absolutely imperative, like when you have to do a test from the inside. For the external tests I use a Windows XP machine with Cygwin (www.cygwin.com) and VMware (www.vmware.com) most linux exploits compile fine under cygwin, if they don't then I shove them into vmware where I have virtual machines of Red Hat, Mandrake and Win2k boxes. In case that doesnt work, the system also dual boots Red Hat 9 and often I'll just work everything out from there.

I feel the advantage of using a microsoft platform often comes from the fact that 90% of your targets may be microsoft systems. However the flexibility under linux is incomparable, it is truely the OS of choice for any serious hacker.. and as a result, for any serious security professional. There is no best O/S for penetration testing -- it depends on what you need to test at a point in time. That's one of the main reasons for having so many different operating systems set up, because you're very likely to be switching between them for different tasks.

If I don't have the option of using my own machine, I like to choose any linux variant.
I keep my pen-tests strictly to the network level, there is no social engineering involved or any real physical access testing other than basic server room security and workstation lockdown (I don't go diving in dumpsters for passwords or scamming employees).

I try as far as possible to determine the Rules Of Engagement with an admin or some other technically adept person with the right authorisation, not a corporate type. This is very important because if you do something that ends up causing trouble on the network, its going to make you look very unprofessional. It's always better to have it done clearly in writing -- this is what you are allowed to do.

I would recommend this even if you're an admin conducting an in-house test. You can get fired just for scanning your own network if its against your corporate policy. If you're an outside tester, offer to allow one of their people to be present for your testing if they want. This is recommended as they will ultimately be fixing most of these problems and being in-house people they will be able to put the results of the test in perspective to the managers.

Tools

I start by visiting the target website, running a whois, DNS zone transfer (if possible) and other regular techniques which are used to gather as much network and generic information about the target. I also like to pick up names and email addresses of important people in the company -- the CEO, technical contacts etc. You can even run a search in the newsgroups for @victim.com to see all the public news postings they have made. This is useful as a lot of admins frequent bulletin boards for help. All this information goes into a textfile. Keeping notes is critically important, it's very easy to forget some minor detail that you should include in your end report.

Now for a part of the arsenal -- not in any order and far from the complete list.

Nmap - Mine (and everyone elses) workhorse port scanner with version scanning, multiple scan types, OS fingerprinting and firewall evasion tricks. When used smartly, Nmap can find any Internet facing host on a network.

Nessus - My favourite free vulnerability scanner, usually finds something on every host. Its not too stealthy though and will show up in logs (this is something I don't have to worry about too much).

Retina - A very good commercial vulnerability scanner, I stopped using this after I started with nessus but its very very quick and good. Plus its vulnerability database is very up-to-date.

Nikto - This is a webserver vulnerability scanner. I use my own hacked up version of this perl program which uses the libwhisker module. It has quite a few IDS evasion modes and is pretty fast. It is not that subtle though, which is why I modified it to be a bit more stealthy.

Cisco Scanner - This is a small little windows util I found that scans IP ranges for routers with the default password of 'cisco'. It has turned up some surprising results in the past and just goes to show how even small little tools can be very useful. I am planning to write a little script that will scan IP ranges looking for different types of equipment with default passwords.

Sophie Script - A little perl script coupled with user2sid and sid2user (two windows programs) which can find all the usernames on a windows box.

Legion - This is a windows file share scanner by the erstwhile Rhino9 security group. It is fast as hell and allows you to map the drive right from in the software.

Pwdump2 - Dumps the content of the windows password sam file for loading into a password cracker.

L0phtcrack 3.0 - Cracks the passwords I get from the above or from its own internal SAM dump. It can also sniff the network for password hashes or obtain them via remote registry. I have not tried the latest version of the software, but it is very highly rated.

Netcat - This is a TCP/UDP connection backend tool, oh boy I am lost without this ! Half my scripts rely on it. There is also an encrypted version called cryptcat which might be useful if you are walking around an IDS. Netcat can do anything with a TCP or UDP connection and it serves as my replacement to telnet as well.

Hping2 - A custom packet creation utility, great for testing firewall rules among other things.

SuperScan - This is a windows based port scanner with a lot of nice options. Its fast, and has a lot of other neat little tools like NetBIOS enumeration and common tools such as whois, zone transfers etc.

Ettercap - When sniffing a switched network, a conventional network sniffer will not work. Ettercap poisons the ARP cache of the hosts you want to sniff so that they send packets to you and you can sniff them. It also allows you to inject data into connections and kill connections among other things.

Brutus - This is a fairly generic protocol brute forcing tool. It can bruteforce HTTP, FTP, Telnet and many other login authentication systems. This is a windows tool, however I prefer Hydra for linux.

Bunch of common exploits effeciently sorted

This is my collection of exploits in source and binary form. I sort them in subdirectories by operating system, then depending on how they attack - Remote / Local and then according to what they attack - BIND / SMTP / HTTP / FTP / SSH etc etc. The binary filenames are arbitrary but the source filenames instantly tell me the name of the exploit and the version of the software vulnerable.

This is essential when you're short on time and you need to 'pick one'. I don't include DoS or DDoS exploits, there is nobody I know who would authorise you to take down a production system. Don't do it -- and tell them you arent doing it.. and only if they plead with you should you do it.

Presenting Reports

This is the critical part -- it's about presenting what you found to people who probably don't understand a word of what your job is about other than you're costing them money. You have to show them that there are some security problems in your network, and this is how serious they might be.

A lot of people end the pen-test after the scanning stage. Unless someone specifically tells me to do this, I believe it is important you exploit the system to at least level 1. This is important because there is a very big difference in saying something is vulnerable and actually seeing that the vulnerability is executable. Not to mention when dealing with a corporate type, seeing 'I gained access to the server' usually gets more attention than 'the server is vulnerable to blah blah'.

After you're done, make a VERY detailed chronological report of everything you did, including which tools you used, what version they are, and anything else you did without using tools (eg. SQL injection). Give gory technical details in annexes -- make sure the main document has an executive summary and lots of pie charts that they can understand. Try and include figures and statistics for whatever you can.

To cater to the admins, provide a report for each host you tested and make sure that for every security hole you point out, you provide a link to a site with a patch or fix, . Try to provide a link to a site with detailed information about the hole preferably bugtraq or some well known source -- many admins are very interested in these things and appreciate it.

A Brief Walk-through of an Attack

This is an account of how an attacker in the real world might go about trying to exploit your system. There is no fixed way to attack a system, but a large number will follow the similar methodology or at least the chain of events.

This section assumes that the attacker is moderately skilled and moderately motivated to breaking into your network. He/She has targeted you due to a specific motive -- perhaps you sacked them, or didn't provide adequate customer support (D-link India are you listening ? ;)). Hopefully this will help you figure out where your network might be attacked, and what an attacker might do once they are on the inside.

Remember that attackers will usually choose the simplest way to get into the network. The path of least resistance principle always applies.

Reconnaissance & Footprinting

Here the attacker will try to gather as much information about your company and network as they can without making a noise. They will first use legitimate channels, such as google and your company webpage to find out as much about you as they can. They will look for the following information:

• Technical information is a goldmine, things like a webpage to help your employees log in from home will be priceless information to them. So also will newsgroup postings by your IT department asking how to set up particular software, as they now know that you use this software and perhaps they know of a vulnerability in it.

• Personal information about the company and its corporate structure. They will want information on the heads of IT departments, the CEO and other people who have a lot of power. They can use this information to forge email, or social engineer information out of subordinates.

• Information about your partners. This might be useful information for them if they know you have some sort of network connection to a supplier or partner. They can then include the supplier's systems in their attack, and find a way in to your network from there.

• General news. This can be useful information to an attacker as well. If your website says that it is going down for maintenance for some days because you are changing your web server, it might be a clue that the new setup will be in its teething stages and the admins may not have secured it fully yet.

They will also query the whois databases to find out what block of IP addresses you own. This will give them a general idea of where to start their network level scans.
After this they will start a series of network probes. The most basic of which will be to determine if you have a firewall, and what it protects. They will try and identify any systems you have that are accessible from the Internet.

The most important targets will be the ones that provide public services. These will be :

• Webservers - usually the front door into the network. All webserver software has some bugs in it, and if you're running home made CGI scripts such as login pages etc, they might be vulnerable to techniques such as SQL injection.

• Mail servers - Sendmail is very popular and most versions have at least one serious vulnerability in them. Many IT heads don't like to take down the mail server for maintenance as doing without it is very frustrating for the rest of the company (especially when the CEO doesn't get his mail).

• DNS servers - Many implementations of BIND are vulnerable to serious attacks. The DNS server can be used as a base for other attacks, such as redirecting users to other websites etc.

• Network infrastructure - Routers and switches may not have been properly secured and may have default passwords or a web administration interface running. Once controlled they can be used for anything from a simple Denial of Service attack by messing up their configurations, to channeling all your data through the attackers machine to a sniffer.

• Database servers - Many database servers have the default sa account password blank and other common misconfigurations. These are very high profile targets as the criminal might be looking to steal anything from your customer list to credit card numbers. As a rule, a database server should never be Internet facing.

The more naive of the lot (or the ones who know that security logs are never looked at) may run a commercial vulnerability scanner such as nessus or retina over the network. This will ease their work.

Exploitation phase

After determining which are valid targets and figuring out what OS and version of software they are using (example which version of Apache or IIS is the web server running), the attacker can look for an exploit targeting that particular version. For example if they find you are running an out of date version of Sendmail, they will look for an exploit targeting that version or below.

They will first look in their collection of exploits because they have tested these. If they cannot find one, they will look to public repositories such as http://www.packetstormsecurity.nl. They will probably try to choose common exploits as these are more likely to work and they can probably test them in their own lab.
They will run this exploit on the target (say the webserver) and if it works, they will have some kind of access to the network.

From here they have already won half the game as they are behind the firewall and can probably see a lot more of the internal network than you ever intended for them to. Many networks tend to be very hard to penetrate from the outside, but are woefully unprotected internally. This hard exterior with a mushy interior is a recipe for trouble -- an attacker who penetrates the first line of defense will have the full run of your network.

After getting in, they will also probably install backdoors on this first compromised system to provide them with many ways in, in case their original hole gets shut down. This is why when you identify a machine that was broken into, it should be built up again from scratch as there is no way of knowing what kind of backdoors might be installed. It could be tricky to find a program that runs itself from 2:00AM to 4:00AM every night and tries to connect to the attackers machine. Once they have successfully guaranteed their access, the harder part of the intrusion is usually over.

Privilege Escalation phase

Now the attacker will attempt to increase his security clearance on the network. He/She will usually target the administrator accounts or perhaps a CEO's account. If they are focused on a specific target (say your database server) they will look for the credentials of anyone with access to that resource. They will most likely set up a network sniffer to capture all the packets as they go through the network.

They will also start manually hunting around for documents that will give them some interesting information or leverage. Thus any sensitive documents should be encrypted or stored on systems with no connection to the network. This will be the time they use to explore your internal network.

They will look for windows machines with file sharing enabled and see what they can get out of these. Chances are if they didn't come in with a particular objective in mind (for example stealing a database), they will take whatever information they deem to be useful in some way.

Clean Up phase

Now the attacker has either found what they were looking for, or are satisfied with the level of access they have. They have made sure that they have multiple paths into the network in case you close the first hole. They will now try to cover up any trace of an intrusion. They will manually edit log files to remove entries about them and will make sure they hide any programs they have installed in hard to find places.

Remember, we are dealing with an intruder who is moderately skilled and is not just interested in defacing your website. They know that the only way to keep access will be if you never know something is amiss. In the event that there is a log they are unable to clean up, they may either take a risk leaving it there, or flood the log with bogus attacks, making it difficult for you to single out the real attack.

Where Can I Find More Information ?

Without obviously plugging our site too much, the best place for answers to questions relating to this article is in our forums. The Security/Firewalls Forum is the best place to do this -- so you can ask anything from the most basic to the most advanced questions concerning network security there. A lot of common questions have already been answered in the forums, so you will quite likely find answers to questions like 'Which firewall should I use ?'.

As far as off-site resources are concerned, network security is a very vast field and there is seemingly limitless information on the subject. You will never find information at so-called hacker sites full of programs. The best way to learn about network security is to deal with the first word first -- you should be able to talk networking in and out, from packet header to checksum, layer 1 to layer 7.

Once you've got that down, you should start on the security aspect. Start by reading a lot of the papers on the net. Take in the basics first, and make sure you keep reading. Wherever possible, try to experiment with what you have read. If you don't have a home lab, you can build one 'virtually'. See the posts in the Cool Software forum about VMware.

Also, start reading the security mailing lists such as bugtraq and security-basics. Initially you may find yourself unable to understand a lot of what happens there, but the newest vulnerabilities are always announced on these lists. If you follow a vulnerability from the time its discovered to when someone posts an exploit for it, you'll get a very good idea of how the security community works.. and you'll also learn a hell of a lot in the process.

If you're serious about security, it is imperative that you learn a programming language, or at least are able to understand code if not write your own. The best choices are C and assembly language. However knowing PERL and Python are also valuable skills as you can write programs in these languages very quickly.

For now, here are a few links that you can follow for more information:

www.securityfocus.com - A very good site with all the latest news, a very good library and tools collection as well as sections dedicated to basics, intrusion detection, penetration testing etc. Also home of the Bugtraq mailing list.

www.sans.org - A site with excellent resources in its reading room, people who submit papers there are trying for a certification and as a result its mostly original material and of a very high calibre.

www.security-portal.com - A good general security site.

www.cert.org - The CERT coordination center provides updates on the latest threats and how to deal with them. Also has very good best practice tips for admins.

www.securityfocus.com/archive/1 - This is the link to Bugtraq, the best full disclosure security mailing list on the net. Here all the latest vulnerabilities get discussed way before you see them being exploited or in the press.

www.insecure.org - The mailing lists section has copies of bugtraq, full disclosure, security-basics, security-news etc etc. Also the home of nMap, the wonderful port scanner.

seclists.org - This is a direct link to the security lists section of insecure.org.

www.grc.com - For windows home users and newbies just interested in a non technical site. The site is home to Shields Up, which can test your home connection for file sharing vulnerabilities, do a port scan etc, all online. It can be a slightly melodramatic site at times though.

www.eeye.com - Home of the Retina Security Scanner. Considered the industry leader. The E-Eye team also works on a lot of the latest vulnerabilities for the windows platform.

www.nessus.org - Open source vulnerability scanner, and IMNSHO the best one going. If you're a tiger team penetration tester and you don't point nessus at a target, you're either really bad at your job or have a very large ego. If there's a vulnerability in a system, nessus will find it.

www.zonelabs.com - ZoneAlarm personal firewall for windows, considered the best, and also the market leader.

www.sygate.com - Sygate Personal Firewall, provides more configuration options than ZoneAlarm, but is consequently harder to use.

www.secinf.net - Huge selection of articles that are basically windows security related.

www.searchsecurity.com - A techtarget site which you should sign up for, very good info. Chris writes for searchnetworking.com its sister site.. I don't think the references could be much better.

www.packetstormsecurity.nl - The largest selection of tools and exploits possible.

πηγη

Επαναφορά Δεδομένων από Κατεστραμμένους Δίσκους, CD και DVD

Και εκεί που όλα πήγαιναν καλά, ξαφνικά ο υπολογιστής δεν μπαίνει στα Windows! Φωνάζετε έναν γνωστό σας, αν δεν γνωρίζεται πως να διορθώσετε το πρόβλημα , και προς έκπληξή σας αντιλαμβάνεστε ότι ο δίσκος χτύπησε.
Λέγοντας χτύπησε εννοούμε ότι δεν μπορεί να λειτουργήσει καθόλου. Υπάρχει βέβαια και η πιθανότητα ο δίσκος να είναι μια χαρά και πάλι να μην μπορεί να φορτώσει τα Windows, το οποίο είναι βέβαια και το πιο σύνηθες. Σε αυτές τις περιπτώσεις τα αρχεία μας υπάρχουν και μπορούμε εύκολα να τα ανακτήσουμε αν συνδέσουμε τον δίσκο σε έναν άλλο υπολογιστή. Τι γίνεται όμως στην περίπτωση του χτυπημένου δίσκου και πώς μπορούμε να επαναφέρουμε τα δεδομένα?

Κατά καιρούς έχουν δημιουργηθεί κάποια φοβερά προγράμματα που μπορούν να κάνουν αυτή τη δουλειά. Πρόσφατα κλήθηκα να επαναφέρω τα δεδομένα από έναν δίσκο και σας παρουσιάζω τα προγράμματα που μπορείτε να χρησιμοποιήσετε.

Στην περίπτωσή μου, έχοντας έναν δίσκο WD 20GB κατάφερα να επαναφέρω 48.059 αρχεία από τα 49.426 τα οποία είναι 10.8GB δεδομένων και αποτελούν το 97,2% των συνολικών δεδομένων του δίσκου. Όχι κι άσχημα!!

Κατεστραμμένα CD/DVD:
Το καλύτερο πρόγραμμα, κατά την γνώμη μου, είναι το CD Recovery, που έχει δυνατότητα ανάκτησης δεδομένων ακόμα και από δίσκους BlueRay και HD-DVD!!! Είναι δωρεάν και μπορείτε να το κατεβάσετε από εδώ!

Κατεστραμμένοι δίσκοι:
Όσο αναφορά τους δίσκους, δύο εργαλεία που σκίζουν είναι το Hard Drive Mechanic (70 $) και το MHDD το οποίο είναι και δωρεάν!!

Βέβαια, ανάλογα τον κατασκευαστή του κατεστραμμένου δίσκου υπάρχουν και τα παρακάτω εργαλεία:

Για δίσκους Seagate Maxtor and Quantum κατεβάστε αυτό.
Για δίσκους Samsung κατεβάστε αυτό ή αυτό.
Για δίσκους Hitachi και IBM κατεβάστε αυτό.
Τέλος, για δίσκους Fujitsu κατεβάστε αυτό.

Ελπίζω να μην βρεθείτε ποτέ στην ανάγκη τέτοιων δεδομένων, εκτός αν δεν πρόκειται για δικό σας δίσκο!!

VoIP σημαίνει Δωρεάν Εικονοτηλέφωνο (Skype Me!)

Εσύ έβαλες τον VoIP σπίτι σου?

Το να ξέρεις τι είναι το VoIP και να μην το χρησιμοποιείς είναι σαν να πεινάς και να μην θέλεις να φας!

Αν πάλι δεν ξέρεις τι είναι, καιρός να μάθεις!

Τα αρχικά "VoIP" σημαίνουν Voice over IP, αλλά αυτό είναι μία άχρηστη πληροφορία!

Σε απλά Ελληνικά VoIP σημαίνει τηλέφωνο μέσω Internet!


Γιατί να το χρησιμοποιήσεις?
Μα για να μιλάς ΤΖΑΜΠΑ όση ώρα θέλεις!

Λες να είναι δύσκολο?
Είναι λίγο πιο εύκολο από το τηλέφωνο του σπιτιού σου!

Πάμε στο ζουμί...

Μπορείς να μιλάς από Υπολογιστή σε Υπολογιστή, από Τηλέφωνο σε Τηλέφωνο και από Υπολογιστή σε τηλέφωνο!
Μόνη προϋπόθεση: Να έχεις Internet!

Πως το κάνεις:

Από Υπολογιστή σε υπολογιστή:

Χρειάζεσαι : (H web camera προαιρετικά).
Το μόνο που έχεις να κάνεις είναι να κατεβάσεις ένα πρόγραμμα που να υποστηρίζει Internet Call. Τα τηλέφωνα που μπορείς να πάρεις είναι απεριόριστης διάρκειας. Αν διαθέτεις κάποια web camera μπορείς να επιτρέψεις στους άλλους να σε βλέπουν και αντίστοιχα να βλέπεις τους άλλους. Μία καταπληκτική δυνατότητα είναι η ομαδική συζήτηση. Μπορείς δηλαδή να βλέπεις και να μιλάς σε πολλά άτομα ταυτόχρονα!



To πιο γνωστό VoIP πρόγραμμα είναι το Skype. Υποστηρίζει κλήση video που είναι και δωρεάν!
Είναι κάτι σαν το MSN Messanger, μόνο που μπορείς να παίρνεις τηλέφωνο σε όλα τα τηλέφωνα είτε είναι σταθερά, είτε κινητά είτε είναι κάποιος άλλος υπολογιστής με skype!
Σε κινητά και σταθερά υπάρχει χρέωση η οποία είναι ελάχιστη!



To MSN messenger σου επιτρέπει να παίρνεις τηλέφωνο αλλά υποστηρίζει και video-κλήση. Είναι πολύ εύκολο στη χρήση και αν δεν το έχεις καλό είναι να το κατεβάσεις. Δεν μπορείς να πάρεις τηλέφωνο σε σταθερό η σε κινητό παρά μόνο σε άλλο υπολογιστή.



Το Jaxtr σου δίνει την δυνατότητα να συνδέσεις τους διαφορετικούς λογαριασμούς MSN και Skype που έχεις μαζί με το τηλέφωνό σου και άλλες 17 υπηρεσίες όπως uTube και e-bay.
Έτσι μέσω αυτού του προγράμματος μπορείς να ελέγχεις τα πάντα!



Ένα ακόμα πρόγραμμα που ξεχωρίζει είναι το VoipBuster. Ξεχωρίζει γιατί έχει πιο χαμηλές τιμές από αυτές του Skype (για τα κινητά και σταθερά τηλέφωνα) και επιπλέον σου επιτρέπει να μιλάς με 35 χώρες δωρεάν!




Από Τηλέφωνο σε Τηλέφωνο:
Χρειάζεσαι: Ένα τηλέφωνο VoIP

Εξωτερικά είναι ίδιο με το κλασικό τηλέφωνο και κοστίζει τα ίδια, μόνο που αυτό δεν σε χρεώνει! Μπορείς να το βρεις σε όλα τα καταστήματα υπολογιστών. Ιδιαίτερη προσοχή πρέπει να δώσεις στην επιλογή της συσκευής για να έχεις την δυνατότητα να παίρνεις τηλέφωνα. Φυσικά, θα πρέπει να υπάρχει ασύρματο δίκτυο internet στην περιοχή που θα το χρησιμοποιήσεις.
Αν και η συσκευή του άλλου είναι τηλέφωνο Voip, μπορείτε να μιλάτε δωρεάν από κινητό σε κινητό!
Η χρήση του είναι ίδια με τα υπόλοιπα τηλέφωνα: Γράφεις τον αριθμό και καλείς...


Από Υπολογιστή σε Τηλέφωνο:
Είναι μία μίξη των άλλων δύο. Μπορείς να πάρεις τηλέφωνο από ένα κινητό Voip σε ένα υπολογιστή και αντίστροφα. Επίσης μπορείς να πάρεις από υπολογιστή σε οποιοδήποτε κινητό ή σταθερό αλλά με κάποια μικρή χρέωση (μικρότερη του OTE).




Για το πώς λειτουργεί η τεχνολογία του VoIP, κάνε click εδώ.