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VPN with Overlapping Networks

When connecting two sites together using a Virtual Private Network (VPN), a common issue that is encountered is trying to build a VPN with overlapping networks — where both sites happen to use the same Private IP addresses. In such cases, hosts on one side of the VPN tunnel will be unable to communicate with […]

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Cisco NAT Terminology

Cisco has created some NAT terminology which explicitly refer to the IP addresses and/or ports involved in Network Address Translation (NAT). While discussing the addresses involved in a NAT, using the terms like “Source” and “Destination” are common. However, using such terms can create some ambiguity. Specifically, the terms “Source” and “Destination” can create confusion […]

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BGP Oldest Path

BGP is the predominant dynamic routing protocol used to exchange routes between different autonomous systems. BGP’s popularity lies in the Path Selection process which allows extremely granular control of the path for incoming and outgoing traffic. One of the steps in this process states that if a tie still exists between two paths, BGP will […]

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Communication through Multiple Switches

In a previous article we demonstrated how a single switch functions. One of the most frequent requests I receive is asking how the process would be different if there were multiple switches. This article will illustrate the process using two switches. In the Packet Traveling series, we discussed the four specific functions of a switch: Learning, Flooding, Forwarding, […]

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Routing Between VLANs

We wrote an article which covers Virtual Local Area Networks (VLANs) as a concept, and another article on configuring VLANs on Cisco witches. The remaining subject to cover is the different options that exist for routing between VLANs. Why do we need Routing Between VLANs? As we learned in a prior article, VLANs create a logical separation […]

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Configuring VLANs on Cisco Switches

We’ve before written about VLANs and what they can do as a concept. This article will focus on configuring VLANs on Cisco switches. We will look at each command necessary to configure the topology below. If this topology looks familiar, it is because you saw it in the article which described how VLANs operated on […]

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Virtual Local Area Networks (VLANs)

Virtual Local Area Networks, or VLANs, are a very simple concept that has been very poorly defined by the industry. This article will explain VLANs from a practical perspective. It will be framed around the two major functions of VLANs, and concluded with an explanation of the idea behind the Native VLAN. Finally, at the […]

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EIGRP Feasibility Condition

EIGRP is a routing protocol whose strategy to prevent routing loops is based upon what is known as the EIGRP Feasibility Condition. EIGRP also makes use of another concept called Split Horizon, which we will also briefly touch on later in this article. To properly discuss the Feasibility Condition however, you must have an understanding […]