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Gratuitous ARP

We’ve talked about Traditional ARP, where a node is requesting another node’s MAC address. We’ve also talked about Proxy ARP, where a node is answering an ARP request on behalf of another node. Which brings us to another iteration of ARP known as Gratuitous ARP. A Gratuitous ARP is an ARP Response that was not prompted […]

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Proxy ARP

We’ve discussed the use cases and role of traditional ARP in the prior article of this series. In this article we will discuss Proxy ARP and its role and significance. Proxy ARP occurs when one node is responding to an ARP request on behalf of another node. Proxy ARP is not a malicious event, it […]

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Traditional ARP

As we’ve learned before, the Address Resolution Protocol (ARP) is the process by which a known L3 address is mapped to an unknown L2 address. The purpose for creating such a mapping is so a packet’s L2 header can be properly populated to deliver a packet to the next NIC in the path between two […]

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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 […]

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EIGRP Metric

The EIGRP Metric has caused confusion for many network engineers trying to understand the protocol. This article will dive into what the metric is, and how to boil it down into its simplified form. Formula and K-Values EIGRP is a Cisco Proprietary routing protocol created in the 1980s. As such, Cisco was the only vendor […]