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Rethinking the Network

Marten Terpstra

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Top Stories by Marten Terpstra

IP Multicast is one of those technologies that most everyone loves to hate. It’s almost the perfect example of how complicated we have made networking. Getting IP Multicast to run depends on several protocols that are all somewhat intertwined or dependent on each, their relationship sometimes explicit, sometimes implicit. Even trying to describe the basic operation is complicated. When an application or service provides information using IP multicast, it simply starts sending it onto a specific multicast group. The multicast router for the subnet of the sender sees the incoming multicast packet and will initially have no forwarding information for that stream in its forwarding hardware. The packet is passed onto the CPU of that router, which will encapsulate this packet and send it towards a special multicast router designated the Rendez-vous Point (RP). When the RP... (more)

Changing the Way We Configure and Provision Our Networks

Some people believe good or bad things always happen in threes. I believe you will always be able to find three (and probably more) things that are good or bad and somewhat related, but sometimes I get surprised by the apparent coincidental appearance of several closely related “things”. Last week the folks at networkheresy.com posted a second installment of their “policy in the datacenter” discussion, Cisco announced the acquisition of tail-f and internal to Plexxi we had several intense architectural discussions around Configuration, Provisioning and Policy management. Maybe we... (more)

Graph Theory and Calculating Network Topologies

Over the past few weeks I have had several conversations related to calculating network topologies and how packet forwarding is done based on those topologies. I wrote this post about a year ago explaining some of these details, but after a conversation with a customer earlier this week, I wanted to explain in a little more detail and relate it not only to Shortest Path First methods, but also to more traditional L1 traffic engineering and path creation. Graphs Any network can be represented as a graph. The switches in the network are the vertices or nodes in the praph, the link... (more)

Open Compute, Open Switch API and Open Network Install Environment

Much has been published about the Open Compute Project. Initiated by Facebook, it has become an industry effort focused on standardization of many parts and components in the datacenter. Initially focused on racks, power and server design, it has also added storage and now networking to its fold. Its goal is fairly straightforward: “how can we design the most efficient compute infrastructure possible”, a direct quote from its web site. The focus of OCP has been mostly around hardware designs and specifications. If you look at the networking arm of OCP, you find several Top of Rack... (more)

Scripting Is Automation, But Automation Is Not Scripting

Last week Greg Ferro (@etherealmind) wrote this article about his experience with scripting as a method for network automation, with the ultimate conclusion that scripting does not scale. Early in my career I managed a small network that grew to be a IP over X.25 hub of Europe for a few years providing many countries with their first Internet connectivity. Scripts were everywhere, small ones to grab stats and create pretty graphs, others that continuously checked the status of links and would send emails when things went wrong. While it is hard to argue with Greg’s complaints per... (more)