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So, at this point, we know that we're trying to reduce routing table sizes.

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If I have routers 1, 2, and 3 here, and then I have a bunch of routers in the

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middle,

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well, this entire domain could essentially be a, or converted to a list domain,

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where

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we have list sites out here, and these list sites participate through this

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tunneling mechanism.

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So what exactly do we mean by separating out the identity and the locator?
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So what exactly do we mean by separating out the identity and the locator?

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Well, in Cisco's view, when we have an IP address, let's just do classic IPv4

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at this

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point, IPv6 would apply to as well.

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But I view this IPv4 subnet to represent two things.

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Because let's say we have subnet A over here, I'm going to say that that subnet

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represents

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the identifier for those hosts, and we could get so granular as to say that it

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identifies

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specific hosts on a slash 32, but at a minimum, that subnet tells me the
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specific hosts on a slash 32, but at a minimum, that subnet tells me the

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identity of that

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particular network.

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But it also tells me the location.

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Because in a classic environment, route or two is going to have to advertise A,

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and we're

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all going to know where A lives, and we're all going to have a route that

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points towards

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A, so that if a packet arrives somewhere on these routers up here, that they

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have a path

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to A.

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They know the location of A because it exists in their routing table.

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Well, Cisco is trying to say we're going to divide these two concepts and treat
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Well, Cisco is trying to say we're going to divide these two concepts and treat

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them differently.

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We're going to keep this as the identifier.

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I mean, subnet A is still the identifier, but I'm no longer going to treat it

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as the location.

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Instead, I'm going to point the location now to router two, and specifically an

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IP address

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on router two, usually a loopback, that we refer to as that routing locator or
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on router two, usually a loopback, that we refer to as that routing locator or

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the RLoc.

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The subnet takes on a different term, we call the endpoint identifier.

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So we have EIDs and we have RLocs, and those are going to show up a lot

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throughout the

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list conversation.

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So what does this look like?

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Well, we're going to divide this conversation into sort of like what Cisco did

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to identity

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and location.

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Hey, so we're going to start with a control plane conversation, and then we'll

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move to

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a data plane conversation.
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a data plane conversation.

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So as we said before, everybody needs access to the routes.

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And as a result, we're going to have to have a database that's accessible by

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everybody,

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and we'll learn that this database is known as a map resolver or an MR.

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And it is going to have all the routes that again are accessible by all of the
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And it is going to have all the routes that again are accessible by all of the

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routers.

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How do the routes get there?

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Well, this is part of the control plane of operation.

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Part 2 is going to register subnet A, and so there is subnet A listed among all

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of the

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other subnets that have been registered to this map resolver.

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So we've done the registration process.

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Now a packet arrives on router 1, and router 1 doesn't have a route to subnet A
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Now a packet arrives on router 1, and router 1 doesn't have a route to subnet A

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.

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But what it does nav is, first of all, it knows where all the other routers in

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the environment

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are. So I do know where all of the R locks are, which is important because that

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is now the

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location that I would need to go to.

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I just need to know which one of these are locks to use.

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So I mean, I can send this to router 2.

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I can send this to router 3.

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I might have 50 other routers I could send it to, which one?

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Well, that is where I'm going to go down and ask the database for.
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Well, that is where I'm going to go down and ask the database for.

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I'm going to use what we might refer to as a poll method rather than a push

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method.

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A push method would say, "Hey, I know where subnet A lives.

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I'm going to push that route to you.

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You're going to push that route to everyone else, and we're all going to know

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where subnet

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A lives."

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Even if we don't need to know where subnet A lives, we're pushing it everywhere

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.

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Well, that's not what we're doing at all.

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I'm actually keeping this a secret, so to speak.

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Maybe not a great secret because I do share it.

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I do tell the database server about it.
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I do tell the database server about it.

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The database server is going to note actually a pairing to say, "A" is attached

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to this specific

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RLock.

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This is the EID is subnet A, and the RLock is going to be router 2.

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Whatever IP address we're using for router 2, again, you probably will loop

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back address.

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I pull that information.

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Everyone is going to look at the database and say, "Hey, I need this pairing,"

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and so it sends

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it back, and it says that A is attached to router 2.
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it back, and it says that A is attached to router 2.

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Unfortunately, because I have all the routes to my RLock, I can just say, "Okay

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, cool.

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Now I'm going to send it into the network."

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Well, there's a big caveat to what we're about to do here, because I need to

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change the

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destination.

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The destination currently, current destination, is subnet A. Probably an IP

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address specifically

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on subnet A, but either way, we're trying to get to subnet A with the current
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on subnet A, but either way, we're trying to get to subnet A with the current

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packet.

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So, I'm going to have to take that packet, and I'm going to have to insert it

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into an encapsulation.

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Other IP encapsulation, this time, so A is hidden in here now in the inner

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packet, but now I have

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an actual destination of the RLock for router 2.

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This forms a tunnel from between router 1 and router 2.
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This forms a tunnel from between router 1 and router 2.

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I'm sending it to this router.

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This router doesn't have to check the database because the destination is just

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router 2, and

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we all know where router 2 is.

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So, I send it down, and I send it down to router 2.

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Router 2 de-incapsulates it, so now we're talking about stripping off that

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header, recovering

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the original packet, and sending it down to the destination.

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This whole conversation we just had is the data plane aspect of Lisp.

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The control plane is all about giving us access to the routes, and the
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The control plane is all about giving us access to the routes, and the

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propagation of that

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information.

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The data plane involves tunneling our traffic from one RLock to another, from

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one edge router

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to another.

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Specifically, this is going to use in a form of IP and IP, so we're going to

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place it

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into another IP layer 3 packet.

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This supports IPv4 and IPv6, by the way.
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This supports IPv4 and IPv6, by the way.

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And importantly, it's going to use UDP.

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Furthermore, on top of all of that, we're actually going to add a shim header

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in here, and shim

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headers usually just kind of get squeezed into the middle between the inner and

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the outer

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header, and this is going to contain some Lisp information in here.

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Now, at this point, an important question we might ask ourselves is, why are we

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studying

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Lisp?

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Because Lisp is a service provider protocol, and service provider is a whole
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Because Lisp is a service provider protocol, and service provider is a whole

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other set

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of exams, and I'm here to take the enterprise networking exam, or maybe gear up

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on my enterprise

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networking knowledge, and the enterprise network is all the way over here.

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Here's the enterprise network.

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I don't need to worry about what service providers are doing usually for the

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most part.

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So why are we studying this?

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Well, importantly, we're going to find that Cisco's software defined access

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infrastructure,
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which we have talked about already, is going to use Lisp.

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Here's the kicker.

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It's going to use Lisp for the control plane, but it's not going to use it at

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the data plane.

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And the reason for that is because the Lisp data plane is intended for layer

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three.

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It's IP inside of an IP header.

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And for software to find access, we need layer two, which is why we use the X

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LAN at the

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data plane.

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This is why it's so important for us to be able to split these protocols up and

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talk about
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talk about

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control plane and data plane operations is because if they're fully segregated

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from one

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another, then that means that I can segment that I can pull them apart and say,

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"Okay, well,

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this is all great.

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Lisp is great, but really I just want the control plane part.

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And I'm going to take the control plane part.

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I'm going to put it into another technology, which is exactly what Cisco did

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with SDA."

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So that's why it's so important we understand these important concepts of Lisp.

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A lot of the terminology of Lisp that we're about to dive into is either used
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A lot of the terminology of Lisp that we're about to dive into is either used

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in software

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to find access or parallels, sort of becomes something else inside of software

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to find

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access, but all of the concepts continue to exist.

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So let's go ahead and continue to dive into Lisp knowing full well that this

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does apply

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to us in the enterprise space thanks to software to find access.