We might have mentioned TTL in some of the previous posts related to Ping and Traceroute. TTL or Time To Live is the transmission limit of a given data unit in a TCP/IP or UDP-based computer network.

A data packet with a TTL value of 64 will cease to exist if it hasn't reached its end target in 64 iterations. The purpose of the TTL field is to avoid a situation in which an undeliverable datagram keeps circulating on an Internet system, a system that will eventually become swamped by such immortal datagrams.

DHCP stands for Dynamic Host Configuration Protocol. This protocol is used by DHCP clients to automatically obtain IP addresses. Most ISPs use it to make your life easy and be ready to browse the Internet right after you properly connect your network device.

Four steps, invisible to the user, take place before a host can obtain its IP address.

Sooner or later email blacklists become the nightmare of most system administrators. Long story short - when your email provider is reported as a source of email spam, a lot of your email messages won't reach your family, friends, business partners, loyal and prospective customers alike.

Becoming part of a blacklist isn't what gets other email providers to filter you, it is the way they decide to do so. Blacklisting causes problems when the administrator decides to simply filter out all emails coming from a network device on a blacklist. Medieval doctors did a similar job when taking off an arm to save the patient from an infected finger. Clean email has no chance of reaching its intended location. Decent e-mail service providers usually filter spam, employing methods that utilize multiple filters before deciding whether an email message is spam or not.

Almost all of us enjoy the benefit of a Content Delivery Network, whether we realize it or not. Content Delivery Networks (CDN) also referred as Content Distribution Networks is what you call a system of network hardware containing copies of data located in various geographical locations, depending on the local demand from clients requesting the resources.

Content delivery networks are especially useful for delivering rich media content to users from different geographical locations, avoiding delay and bandwidth overload near the main server. CDNs can contain all types of data, but most often they are used to distribute data which demands high bandwidth. A few rough examples are downloadable software, media files and documentations, multimedia streams, online games as well as database queries, etc.

The end goal of the Denial-of-service attack (DoS attack) or distributed denial-of-service attack (DDoS attack) is to make a resource unavailable to its users. The attack can be carried out on different levels, depending on the target and the people involved. In essence, the attack represents a highly intense attempt by one person or more to hinder websites or specialized internet services from running properly, causing financial losses to that resource's owner.

Depending on the motivation behind the attack, different targets might suffer from it. The attack can be implemented by a single person, carrying out a personal agenda. Such an attack is improbable to cause too much trouble and will only be temporary. A much bigger problem is organized attacks performed by a group of individuals in pursuit of financial gains. Such attacks can be sustained for longer periods of time and might as well ruin companies relying on online presence. Banks, online retailers, government sites, payment gateways, and even root nameservers can become easy prey for organized DDoS attacks.