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 […]
Communication through Multiple Switches
February 9, 2017 By 26 Comments
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, […]
Address Resolution Protocol (ARP)
February 5, 2017 By 3 Comments
An IP address is the logical addressing scheme for nodes on a network. IP Addresses exist at the Network layer of the OSI Model and help facilitate the L3 goal of “end to end” delivery. A MAC address is the physical addressing scheme for individual NIC cards on each node of a network. MAC addresses […]
ARP Probe and ARP Announcement
January 30, 2017 By 7 Comments
We finally come to the last iteration of ARP that this article series will discuss. They are the ARP Probe and the ARP Announcement. Both of these are used in a process known as Duplicate Address Detection. The idea is if a host acquires and puts to use an IP address that happens to already […]
Gratuitous ARP
January 23, 2017 By 27 Comments
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 […]
Proxy ARP
January 16, 2017 By 13 Comments
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 […]
Traditional ARP
January 9, 2017 By Leave a Comment
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 […]
Routing Between VLANs
October 20, 2016 By 36 Comments
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 […]