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On the ‘web: All you ever wanted to know about EIGRP

In episode 5 the Network Collective panel dives deep into the inner-workings of EIGRP and how to tune the protocol to work best for you. This isn’t your run of the mill EIGRP training session though, so buckle up and dig in to learn a lot about a protocol which appears pretty straight forward on the surface.

This last week I was on the Network Collective discussing EIGRP with Nick Russo; even if you think this protocol is dead, it’s well worth watching or listening to. And if this isn’t enough EIGRP for you, the EIGRP book on Addision-Wesley is another good resource.

eigrp-for-ip

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Nonblocking versus Noncontending

“We use a nonblocking fabric…”

Probably not. Nonblocking is a word that is thrown around a lot, particularly in the world of spine and leaf fabric design—but, just like calling a Clos a spine and leaf, we tend to misuse the word nonblocking in ways that are unhelpful. Hence, it is time for a short explanation of the two concepts that might help clear up the confusion. To get there, we need a network—preferably a spine and leaf like the one shown below.

Based on the design of this fabric, is it nonblocking? It would certainly seem so at first blush. Assume every link is 10g, just to make the math easy, and ignore the ToR to server links, as these are not technically a part of the fabric itself. Assume the following four 10g flows are set up—

  • B through [X1,Y1,Z2] towards A
  • C through [X1,Y2,Z2] towards A
  • D through [X1,Y3,Z2] towards A
  • E through [X1,Y4,Z2] towards A

As there are four different paths between these four servers (B through E) and Z2, which serves as the ToR for A, all 40g of traffic can be delivered through the fabric without dropping or queuing a single packet (assuming, of Continue reading

The 40 hour work week

Before 1900 the average American worker worked more than 60 hours a week. A standard schedule was ten-hour days, six days a week. The only structural limits to working were lighting and religion. You stopped working when it was too dark to see or to go to church. It was exhausting. It was often fatal. —Collaborative Fund

The 40 hour work week is foremost a result of the physical limits of the human body—but we often fail to take into account the mental limits, as well. Why was working for more than 40 hours a week on a railroad dangerous? It was not just because people were physically tired, but also because they were mentally tired. The resulting discussion among coders has been rampant and widespread (see, for instance, here).

First, the focus on time and the length of the work week may be a little misdirected. We are still a world focused on physical presence as a proxy for accomplishing work. I know a lot of companies prefer to have people in the office—ironically, this is a big deal with most of the companies in the world that aim to bring networks, and network based services, to the masses. Continue reading

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