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Ethernet Protocol, CSMA/CD, Collisions
Here we see a logical drawing of the Fast Ethernet Data Link Layer sublayers. Data is passed down from the upper layers (such as TCP/IP or Novell Net…
The OSI Model
Here we are going to explain in detail how data travels through the OSI model. You must keep in mind that the OSI model is a guideline. It tells the…
Network Address Translation - NAT
In our previous article, Network Address Translation (NAT) Overload - Part 1, we explained what NAT Overload is and how it works. This page deals wit…
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…

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Netflow Articles:

In this article, we explore the core principles of bandwidth management and examine how modern network monitoring technologies can assist in maintain…
Monitoring network traffic & bandwidth usage via Netflow is mandatory for any type and size network. Gaining visibility into user traffic, applic…
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…

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VLAN Networks
While the VLAN Tagging article briefly covered the IEEE 802.1q protocol this article will continue building upon it by further analyzing the IEEE 802.1q T…
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…
VLAN Networks
Designing and building a network is not a simple job. VLANs are no exception to this rule, in fact they require a more sophisticated approach because of t…
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…

Routing
Our previous article explained the purpose of Link State Update (LSU) packets and examined the Link State Advertisement (LSA) information contained within…
Routing
This is the thrid article of our 6-part OSPF series (see below) that describes how OSPF routers perform neighbor relationship and adjacency. We’ll examine…
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
Open Shortest Path First (OSPF) is a popular routing protocol developed for Internet Protocol (IP) networks by the Interior Gateway Protocol (IGP) working…

SASE & SD-WAN Networks
The Virtual Private Network (VPN) has become the go to security solution for keeping communications between networks and endpoints secure. After all, VPNs…
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…
Palo Alto Networks
During the past decade, we’ve seen the global IT security market flooded with new network security and firewall security appliances. New vendors emerging…
Cisco Switches
The Supervisor Engine is the heart of the Cisco Catalyst 4500 and 6500 series switches. It is the equivalent of an engine in a car. Every packet that ente…