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Domain Name System (DNS)
This section will help you understand how the DNS queries work on the Internet and your home network. There are two ways to use the domain name syste…
Network Protocols
As discussed in the previous tutorial, we were made painfully aware that we were running out of IP address spaces and literally did in 2011. A new…
TCP - UDP Protocol Analysis
This article is an introduction to the 7-page TCP Header analysis section that follows. We briefly view each section of the TCP Header and then move…
Ethernet Protocol, CSMA/CD, Collisions
In this article we will analyze the following aspects of upgrading/migrating from 10Mbit Ethernet to 100Mbit Ethernet. Cabling Incompatible Imple…

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Netflow Articles:

In our previous article we explained how a Netflow Analyzer can help you gain visibility into your user traffic, application traffic and data flows w…
SNMP (Simple Network Management Protocol) and Netflow are both popular protocols with admins, prized for their ability to give visibility over the ne…
This article will cover the basics of Netflow, including its use cases, Netflow supported devices, Netflow history, and variants. We’ll also dive int…
Monitoring network traffic & bandwidth usage via Netflow is mandatory for any type and size network. Gaining visibility into user traffic, applic…

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VLAN Networks
VTP (VLAN Trunking Protocol) pruning is a feature that is used in Cisco switches to reduce unnecessary traffic in VLAN (Virtual Local Area Network) trunks…
VLAN Networks
Dynamic VLANs were introduced to grant the flexibility and complexity(!) that Static VLANs did not provide. Dynamic VLANs are quite rare because of their…
VLAN Networks
We mentioned that Trunk Links are designed to pass frames (packets) from all VLANs, allowing us to connect multiple switches together and independently co…
VLAN Networks
VLANs are usually created by the network administrator, assigning each port of every switch to a VLAN. Depending on the network infrastructure and securit…

Routing
Distance Vector routing protocols use frequent broadcasts (255.255.255.255 or FF:FF:FF:FF) of their entire routing table every 30 sec. on all their interf…
Routing
This is the third article of our OSPF series which analyzes the different OSPF States routers go through during the OSPF discovery and neighbor forming pr…
Routing
This article explains how OSPF uses Link State Advertisement (LSA) to exchange information about the network topology between routers. When a router recei…
Routing
IGRP (Interior Gateway Routing Protocol) is a Cisco proprietary distance-vector routing protocol used in enterprise networks to exchange routing informati…

Cisco Routers
Our Web SSL VPN article written back in 2011 introduced this new wave of VPN services.  This article extends the topic by covering the installation a…
Cisco Routers
MPLS generates Implicit Null label (The Implicit NULL label is the label that has a value of 3) for directly connected interfaces and for the summary rout…
Cisco Routers
Our DMVPN Introduction article covered the DMVPN concept and deployment designs. We explained how DMVPN combines a number of technologies that give it its…
Cisco Routers
This article serves as an extension to our popular Cisco VPN topics covered here on Firewall.cx. While we’ve covered Site to Site IPSec VPN Tunnel Between…