Wednesday, September 30, 2015

Introduction to Multicast IP Addresses

One of the differences between unicast and multicast IP addresses, is that unicast IP addresses represent a single network device while multicast IP addresses represent a group of receivers. IANA has reserved the class D range to use for multicast, which means that we have the through range for IP multicast addresses.

Some of the addresses are reserved and we can’t use them for our own applications.

Sunday, August 30, 2015

Linux Boot Process

Have you ever wondered what happens behind the scenes from the time you press the power button until the Linux login prompt appears?

Booting a Linux installation involves multiple stages and software components, including firmware initialization, execution of a boot loader, loading and startup of a Linux kernel image, and execution of various startup scripts and daemons. For each of these stages and components there are different variations and approach.

Tuesday, June 30, 2015

Introduction to HTTP

The Hypertext Transfer Protocol (HTTP) is a request–response protocol in the client–server computing model that has been in use by the World-Wide Web. HTTP is the foundation of data communication for the World Wide Web.  Whenever you surf the web, your browser will be sending HTTP request messages for HTML pages, images, scripts and styles sheets. Web servers handle these requests by returning response messages that contain the requested resource.

A web browser is an example of a user agent (UA). Other types of user agent include the indexing software used by search providers (web crawlers), voice browsers, mobile apps, and other software that accesses, consumes, or displays web content.

Saturday, May 30, 2015

Security Levels in Cisco ASA

ASA Security Levels are used to define how traffic initiated from one interface is processed. When configuring an ASA with no access-list applied on any of the interface, no access lists are required for traffic from a high security level interface to go through a low security level interface, but the other way around low security level to higher security level is not possible unless we configure an access-list that permits this traffic.

The higher the security level, the more trusted the interface is. Each interface on the ASA is a security zone so by using these security levels we have different trust levels for our security zones.

Thursday, April 30, 2015

Introduction to Spanning Tree Protocol (STP)

The Spanning Tree Protocol (STP) is a protocol that builds a logical loop-free topology for Ethernet networks. The basic function of STP is to prevent bridge loops. Spanning tree also allows a network design to include spare (redundant) links to provide automatic backup paths if an active link fails. This is done without the danger of bridge loops, or the need for manual enabling or disabling of these backup links, leaving a single active path between any two nodes. 

Spanning-Tree Protocol implements the 802.1D IEEE algorithm by exchanging BPDU messages with other switches to detect loops, and then removes the loop by shutting down selected bridge interfaces. This algorithm guarantees that there is one and only one active path between two network devices.