Alright folks, so now we're going to begin our Encore architecture preparation.
So we spent a little bit of time in day one or session number one looking a little bit
at the architecture, the access layer, distribution layer, the core layer, but there are a few
other aspects that we need to grasp to get ready for the certification exam when it comes
to our architecture, such as stateful switchover, non-stop forwarding, our control plane, our
data plane.
We'll even have a discussion here on virtual servers and virtual switches.
So let's begin here by taking a look at stateful switchover and non-stop forwarding.
So first and foremost, stateful switchover, SSO, so if you see that on the exam, SSO,
we're talking about stateful switchover, and if you see NSF, non-stop forwarding, that's
what they're referring to in that particular case.
So remember from day one that we indicated that it's important to have redundancy, and
we are going to have redundancy in our access layer, our distribution layer, our core layer,
our campus backbone, and that's going to come through redundant devices, it's going
to come from redundant links, but let's talk about redundancy within those devices specifically
at this point in time.
What we have to remember is that our devices have a processing aspect associated with them.
So for example, they have the ability to send spanning tree protocol messages.
They have the ability to send dynamic routing protocol messages.
They have the ability to think and make decisions.
So with that in mind, I want you to consider the fact that the brains of the device, this
processing capability of the device could fail, and if that fails, then our device goes
down.
So we need redundancy in the device, and in this particular case, we're talking about
the supervisor module.
Now the supervisor module would be the actual module that goes in the actual device, and
that module would have something known as our route processor.
So the route processor would be like your CPU as an example.
So on the exam, you might see RP for route processor, or you'll see route processor.
They might call it the RP module or the route processor module, or they might call it the
supervisor module or just the supervisor.
So keep in mind that if you see supervisor, supervisor module, route processor, route
processor module, RP module, they're really referring to the same thing in that particular
case.
So we're dealing with something that provides control plane functions, tasks like making
routing decisions, making management decisions, processing our protocols like spanning sheet
protocols, CDP, LLDP, LACP, PEGP, DTP, VTP, EIGRP, OSPF, BGP, and so on and so forth.
And these supervisor modules are typically found in our higher end equipment, so our
modular type of equipment, and it's doing the control functions for us.
So when it comes to the supervisor module, think CPU, the brains of the actual device,
storing and running the operating system, so the Cisco iOS, the iOS XE, controlling
what is going to be done for loading and managing and upgrading the actual software on the device.
It's going to be able to manage and control the hardware components of our device as well,
our line cards, our power supplies, our fans.
It can monitor the status of a multitude of components and take actions depending on things
like hardware failures.
It even has the interface we need to configure and manage our device, whether it's the command
line interface we're talking about or the graphical user interface we're talking about.
It's all part of this supervisor module.
So as you can see, the supervisor module is really, really important.
And if our supervisor module ever fails, then we are out of luck.
Our device is not going to be able to exchange the protocols it needs to, to ultimately build
the tables we need.
So it can ultimately make the forwarding decisions that it needs to make.
So it's really important that when we are dealing with these modular devices, we spend
some extra money and ensure that we have redundancy in regards to the brains, the control plane,
the supervisor module of our devices.
And what you're going to have here is you're going to have now high availability with the
actual control plane.
So if one module fails, then the backup can take over without disrupting operations.
But in order for this to work properly, we need what is called stateful switchover, SSO.
So stateful switchover, what we have is an active and passive scenario.
So we have our two supervisor modules.
One's going to be active and one's going to be passive inside of our chassis.
And this is going to give us the chance to have that uninterrupted functionality that
we need if one of those supervisor modules fails.
So the active one is going to take care of all of the operations.
The second one is going to be synchronized with the first one, folks, right?
So active, passive.
One is doing all the work and the other one is simply synchronized.
So the standby is synchronized with the active.
So they have the exact same configuration, but one's active, one's standby.
So if the active supervisor module fails, the standby one can take care of what needs
to be taken care of at that point in time without interruption, ensuring that there
is minimal or hopefully no downtime when our supervisor module or our route processor,
our RP, fails.
Now what we need to realize is that we're talking about the control plane at this particular
point in time.
I now want to focus on nonstop forwarding.
What is this about?
This is actually about our data and our data plane, whereas SSO is more about the control
plane.
Not more about.
It is the control plane.
Think about our network traffic.
Our network traffic, we want to continue flowing through our device.
So network traffic's coming in.
We want the network traffic to keep going.
Remember, the network traffic is not going to be flowing through our route processor,
our supervisor module.
Right?
This is the brains.
We're going to have line cards in our device, and we want those line cards to continue doing
what?
Continue forwarding.
So our network traffic needs to keep flowing, and this is where NSF comes into play, nonstop
forwarding.
It works together with SSO.
Remember that.
It works together with SSO.
So you have SSO enabled.
You have nonstop forwarding enabled.
Nonstop forwarding needs SSO, but this nonstop forwarding provides what?
It provides Layer 3 uninterrupted network slash routing operations when we have a failure
of the supervisor modules.
So think of protocols like BGP, OSPF, EIGRP.
Those are NSF nonstop forwarding capable protocols.
They're able to detect failure, react accordingly.
So there's no operational interruption, and in a nutshell, what we're saying here is that
when we have SSO with nonstop forwarding enabled, then the supervisor module can fail, and while
the switchover is happening, traffic can continue to flow.
So think about a protocol like OSPF.
OSPF has a hello timer of 30, 30, no it doesn't, 10 seconds, and a dead timer of what?
Four times the hello, so 40 seconds.
So as long as the stateful switchover finishes within what, 40 seconds, then our line cards
can continue to forward based on the information that they previously got, because the neighborship
is still up on the other device, right?
Think about it for a second.
If our route processor fails, then the device on the other side would stop receiving what?
Hello packets.
Therefore, if it stops receiving hello packets within 40 seconds, it's going to tear down
the neighborship.
So with nonstop forwarding enabled, it ensures the device that has the failure keeps forwarding
packets, and as long as the stateful switchover finishes within the dead timer setting, so
40 seconds, well then the other neighbor has no idea we had a problem over here, because
everything just keeps going well, and then stateful switchover finishes, and then those
hello packets are getting exchanged, and everything's good.
The neighboring device has no idea we were affected, or they could have been affected.
Why?
The high availability through redundancy, using things like what?
Supervisor modules, with stateful switchover, and nonstop forwarding enabled.
So line cards can continue forwarding data traffic with nonstop forwarding.
All right, so keep in mind for the exam, if they are focusing the question around redundancy
within a chassis, then they're really talking about the supervisor modules in that particular
question.
So they could be listed as route processor, RP, supervisor modules, but now pay attention
to the details.
If they're talking about control plane, yeah, and you're looking for answer like SSO, stateful
switchover, but if they're talking about network traffic, data plane, traffic flowing through
the device, then they are looking for nonstop forwarding as the answer option, all right?
That's what I want you to take away from this discussion.
So make sure you know what a supervisor module is.
Make sure you know you can have redundant supervisor modules in our modular chassis.
Make sure you realize what stateful switchover is and what nonstop forwarding is to get yourself
ready for the certification exam.