Basics of Network Virtualization Flashcards
we'll cover the basics of Network Virtualization including physical data center network topologies, software defined networking, congestion control, and traffic engineering,
Data center is multi-tenancy. What does it mean?
it means that simultaneously, there could be multiple applications that can be coexisting on the computation resources of the server. The expectation for applications is that they’ll have good performance so that the network capacity is uniform for supporting all the applications that maybe running simultaneously.
Date centers need layer 2 semantics. What does it mean?
ayer 2, is the link layer, so like the Ethernet. When you’re connected on a local area network, your expectation is that at link speed you can communicate with one another. But now you’re going through a network fabric in order to communicate with one another, but yet you expect that all the individual applications will have layer 2 semantics for communication. That is a key property that you want to have in the network fabric. What that also means is that despite the fact that this network fabric is being shared by multiple servers, every one of these applications is thinking that they’re running on a local area network from the point of view of the performance. That’s one of the key properties that you want to build into the routing fabric.
Data centers need uniform network capacity. Why? and what does it mean?
Data centers need uniform network capacity for supporting all the apps. Server-server communication should be bound only by the interface speeds, independent of which servers are hosting a particular app.
Data centers need performance isolation. Explain.
They need performance isolation for the apps. Traffic of one service should not affect another.
What is the role of the routing fabric of a server?
inside a data center, the network is one of the main components of the computational resources in a data center and these networking fabric connects all of the servers that are inside a data center, and it also provides connectivity to the clients that are out here via the internet. So that’s the role of the routing fabric, both for internal communication among these servers inside the data center, as well as for going out on the internet and connecting to the clients that could be anywhere in the world.
What is crossbar interconnection network? what is the downside?
A crossbar interconnection network allows you to connect any element to any other element and all of them can work simultaneously with constant latency for communication, and there is no interference between them, no congestion in the network. So that’s what you really want, but that would not be cost effective.
What is Clos network?
Network named after its designer, Charles Clos. It is a scalable interconnection network for meeting the bandwidth requirements for the end devices using commodity switches, this is the key. So instead of building specialist switching fabric, Charles Clos was able to build using commodity switches network for connecting subscribers in a telephone switching network.
Described the layers of a 3-stage Clos network, assuming we have N machines.
first stage, ingress, consists of m switches, each is nxk (n=in, k-out).
middle stage consists of k switches, each is mxm.
last stage, egress, consists of m switches again, each is kxn.
What is the latency in a 3-stage Clos network?
There is a constant latency between any two hosts, which depends on the number of stages (here its 3)
What property does a Clos network has, if k>=n?
In this case Clos can be non-blocking like a crossbar switch. Meaning, you can arrange these switches in a manner that allows any pair of input-output, so long as they are distinct from each other to be happening simultaneously.
Are there any redundant paths between any 2 hosts in a clos network?
Yes
