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Now in the official search guide that Wendell wrote, he spent a lot of time going over XDA or software

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defined access.

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Now just software defined could be software defined coffee.

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I mean, there's so many terms with this word of software defined networking got abused.

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We had software defined networking that was open flow.

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Then we had software defined networking.

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They were using APIs, we had software defined networking, there was overlays.

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So we spoke about overlays and under laser ready basically became software defined, whatever you like,

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but software defined access or XDA.

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Is Cisco solution of changing the way a enterprise network works?

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So traditionally in an enterprise network, we would have spanning tree that causes a whole bunch of

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issues because we have to match up forwarding of ports to HSP.

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Default gateways causes a whole lot of issues.

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So we want to do away with spanning tree and what we do is we just run routing protocols everywhere.

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So the default gateway of your PCs will be the local access switch.

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So the switch on the edge, the switch that they connect to rather than a call switch or a distribution

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switch, we run OSPF everywhere or routing protocol everywhere.

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So we do away with spanning tree, we do away with port blocking that kind of stuff.

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But in my experience of the CCNA exam, I think it was overkill, the SDA stuff in the OCG.

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Now, if I hear otherwise, I'll change this course.

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But I wouldn't spend too much time on SDA.

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Basically, the idea is the network gets managers of fabric, so we have all these routers and switches

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that are controlled by a controller and then similar to NSX from VMware, what we do is we building

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tunnels automatically VXLAN Tunnels once again where we build an overlay across the underlay network.

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So the core underlay network can be fairly basic rather than configuring a whole bunch of access lists

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on the core devices.

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We can do everything as a policy on the SDA server and then apply a policy on the network devices and

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DNA center will basically build stuff automatically.

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So it will build the VXLAN tunnels, it will apply the policies.

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So we have this concept once again of intent based networking and intent is I want to do something,

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but I don't want to have to explicitly write everything down to make that happen.

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So as an example, I want to stop PCA talking to PCB.

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In a traditional environment, you have to create access lists that stop those devices from talking

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to each other, but with an intent based scenario and, and some of the other controller based implementations,

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I would basically say, okay, this guy can't talk to this guy, put a cross there.

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So that's all done through a GBE as an example.

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And then that applies a policy to the network that basically stops that.

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So you as a network engineer don't have to go and configure access lists manually.

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Your intent is stop this guy talking to this guy and the network just makes that happen automagically,

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which is quite scary in some ways because what happens if it goes wrong?

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So the whole idea of this stuff is fantastic and I don't want to blow it out of the water straight away,

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but just be aware that you should kind of understand what's going on under the hood because what happens

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if something goes wrong?

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But the principle is we have an underlay network, then we put VXLAN tunnels over it, which allows

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us to apply policies on the overlay network rather than on the underlay network.

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So we can stop this guy talking to this guy much more easily using these tunnels then to try and have

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a single access list on an interface of a router that blocks people across the entire network.

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A much better way of doing things.

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It's basically the way it's going.

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So we have a controller that manages a whole bunch of devices in the enterprise.

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Now, just stepping back a second, sorry to jump around.

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Software defined networking was more for the data center so it was NSX was a fantastic success in the

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data center.

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Cisco have ACI also data center product, but what about enterprises?

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So SDA is an enterprise solution where we take software defined principles and apply it to an enterprise

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and we apply policies on that network rather than in a data center.

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So basically simple things like, okay, let's get rid of spanning tree.

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So we run OSPF or routing protocol everywhere.

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Everything's layer three rather than layer two.

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But how do we get this device to talk to this device?

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We can apply a policy through a GOOEY or a management station or a controller if you want to use the

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the right term.

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That applies the policy onto the network without you having to manually configure a whole bunch of stuff.

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The idea is, is this term of abstraction?

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Abstraction is used everywhere.

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As an example, if I want to write a piece of Python code, I don't have to know how to make that do

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something on a hard drive.

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I'm abstracted from the low level programming.

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The operating system abstracts me from the hardware operating system, abstracts me from network cables,

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stuff like that.

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I'm programming in a high level programming language python that goes all the way down through the stack

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and actually make something happen.

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Something happen on the the network.

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So I'm extracted from assembly language as an example.

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I'm abstracted from low level stuff.

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I use my brain for doing high level stuff rather than low level stuff.

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So very real world.

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Example Pilots.

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A pilot today doesn't fly from the UK to the US manually the whole way.

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What do they use?

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They use autopilot.

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So the idea is autopilot allows the pilot to take care of high level tasks while the low level stuff

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is taken care of using autopilot.

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Now the airplane has all of these sensors that give information about altitude, stuff like that, and

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then the plane can guide the pilot.

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But autopilot can cause problems where the pilot tries to manage the network, or should I say the plane

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through autopilot by adjusting various high level parameters rather than just grabbing the plane and

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flying it.

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And there was a really interesting video where they were talking about this issue where automation has

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actually caused crashes because pilots no longer fly the plane like physically fly it.

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They try and adjust the planes flying through autopilot.

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So they they try and feed information to autopilot that then flies the plane and adjusts adjusts the

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plane.

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But if you've got a plane flying at you, you as a pilot should grab the airplane and fly it out of

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the way rather than trying to adjust autopilot.

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And I think that's the same thing that we as network engineers need to be careful of, is don't rely

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on the autopilot or the cleverness of all of these applications.

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When the network is burning or there's a fire, you need to jump in and fix the problems.

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So automation has its place, but it's still important to understand how networks work because automation

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will allow you to break a network very, very quickly if you don't understand what your automation is

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doing.

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I mean, if a programmer just writes a script that sends a whole bunch of beeps into a network running

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spanning tree, it could mess up your whole network.

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So you need to understand what your program is doing, what these applications are doing.

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So there's huge advantages to abstraction, huge advantages to automation, but you still need to understand

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networking.

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So I think Cisco have done a good thing here.

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10% of the CNA is automation and programming or programmability.

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90% is a lot of traditional network stuff.

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You still a network person, it's still a network engineer.

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You still need to understand protocols like spanning tree, OSPF, etc. But I think for me the programming

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side is very exciting because Cisco now have this dev network, so you have this world in front of you

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which didn't exist.

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I'm recording this, you know, not long after the CCMA was released.

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You've got this world now where you can go traditional networking with a bit of programming, or you

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can go programming with a bit of networking.

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So I think if you're starting in your career, you have two wonderful choices.

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And I mean, you just got to decide what you enjoy.

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Do you enjoy programming with a touch of networking or do you enjoy networking with a touch of programming?

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I think those are going to actually become closer and closer in future.

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So five or ten years from today, the line between networking and programming will just draw closer

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and closer.

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Networking is changing, and I've been saying this for many years.

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I mean, now we're going more to the cloud.

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So cloud stuff is becoming more important, but.

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To think that if you put it in the cloud, it's going to solve your network problems.

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It's still a network.

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You still have to manage the network cloud as in your network.

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I mean, if you put a VM in in the cloud, it's cool.

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It's just a VM.

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But what happens if you have virtual machines in Asia and in America and in Europe, suddenly you start

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working with load balancers, you start working with firewalls, you start working with access control

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lists, you start working with VLANs, not call that, but you start working with all the traditional

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networking stuff.

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So just because it's in the cloud doesn't mean that you can ignore networking.

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Still going to be a lot of work for network engineers.

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It's just the roles may change rather than typing on the CLI.

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You might be working in a controller or in the cloud, but you still need to understand networking principles.

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Okay, so that was quite a long ramble, a hope that kind of discussion was valuable to add to the course.

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I'm going to show you some more practical stuff now in the rest of the course, but hopefully that gives

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you a good idea of what's important for the exam and kind of sets the, the 10,000 foot view and overview

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of of programming and network automation.