Russ

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PCIe versus Ethernet in a Composable System

I posted a link to a worth reading story last week about Liqid’s composable hyperconverged system. A reader (Vova Moki) commented on the LinkedIn post with this question—

Although I don’t understand how much faster is the PCIe than regular NICs?

Excellent question! It certainly seems that 100g Ethernet should be much faster than PCIe; this article lists the highest speed of PCIe as 15.8G/s across 16 lanes, with faster speeds expected into the future. Further, PCIe runs on parallel lanes, which means it must be very difficult to build a switch for the technology. The simplest way to build such a switch would be to pull the signals off the 16 different lanes, serialize them into a single packet of some sort, and then push them back out into 16 lanes again (potentially in different order/etc.).

So why should composable systems use something like PCIe, rather than using 100g Ethernet. After all, the Ethernet NIC is essentially doing precisely what a PCIe switch would need to do by pulling the data off a PCIe bus, serializing the data, and sending it over a network to a switch, which can, with the right design, already switch these packets Continue reading

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

The post On the ‘web: All you ever wanted to know about EIGRP appeared first on rule 11 reader.

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

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