Alright, so we've got a list set of terminology that we're going to have to get
familiar with.
So at this point, I'm going to stop numbering routers here, but we are going to
recognize
that this here is our list environment.
Meaning we could have a bunch of other routers inside of this space, kind of
the drawing we
had before there, a bunch of routers, but we do have some router specifically
at the
edge that are going to have subnets attached, probably more than one subnet per
router, but WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
router, but
we get the idea here.
So in general, we're going to have subnets, so again subnet A, B, and C. And as
we start
to build our terminology over here, we're going to, first of all, review a
couple of important
ones.
So here's the terminology.
And the first one is simply the endpoint identifier or the EID.
The endpoint identifier, which again, stands for endpoint here, and point WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
The endpoint identifier, which again, stands for endpoint here, and point
identifier equates
to the subnet.
So even though we call it an endpoint identifier, we might say, okay, well,
that must be a
host on the subnet.
Well, from a list perspective, it's talking about the entire subnet.
That subnet could be a slash 24 or slash 28, a slash 22, doesn't matter.
It is a subnet that gets represented in the list, borrowed as an EID.
We then have the R lock, which stands for the routing locator. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
We then have the R lock, which stands for the routing locator.
And the R lock is going to represent the location address, which again,
typically is going
to be something like loopback zero or something like that, a loopback interface
that is reachable
by everybody else.
These loopback addresses are going to be part of the underlay.
All of the routers inside of this space, knowing where each other are, this in WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
All of the routers inside of this space, knowing where each other are, this in
here is the underlay.
Meanwhile, these routes that are all sort of part of the outer edge where they
can just
go from one subnet to another, that would be the overlay in this example.
So I'll just write it over here as overlaying kind of point to these different
subnets here.
But we can start to make sense of the fact that I as router a here, this edge
router, I
know where this router is, this I know, this down here, I don't know because it WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
know where this router is, this I know, this down here, I don't know because it
's part
of the overlay, not the underlay.
So let's start giving some terms to these routers.
If a packet is coming into one of these routers, then this makes this router
the ITR, the
ITR stands for the Ingress Tunneling Router. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
ITR stands for the Ingress Tunneling Router.
Meanwhile we're bound to go out another router somewhere out here.
So let's say we're going to subnet B, this turns this router into the ETR.
And as we might imagine, from the letters, that stands for the Egress Tunneling
Router.
Now ingress and Egress are just English words that mean in and out.
We're coming into the list domain via the ITR.
We're exiting the list domain via the ETR. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
We're exiting the list domain via the ETR.
Funny enough, these roles can be flipped.
What happens now if we have return traffic?
Well I'm coming in via this bottom router, which turns it into an ITR, and it
exits the
list domain over here via the ETR.
So these are always going to be relative to the traffic flow.
Meaning that I might be an ETR with one packet and an ITR on the next packet, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Meaning that I might be an ETR with one packet and an ITR on the next packet,
which is
why we sometimes just call these XTRs because they really could serve either
role.
Now next let's talk about that database.
Remember, we said that we needed a database that has all of the EID to our lock
mappings.
And this is a mission critical part of the list control plane.
So this actually gets split into two different functions. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So this actually gets split into two different functions.
We have the mapper's allver, as we've already mentioned, and that would be the
MR.
And it also gets a map server or MS role as well.
We're going to define these in a little bit better formly coming up here
because it's
important for us to understand what the difference is.
The reality is that in smaller environments, we simply have one device that is WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
The reality is that in smaller environments, we simply have one device that is
going to
do both.
We have the MS MR or maybe the MRMS depending on who's writing it out.
But either way, we have one device that can do both in a lot of situations.
This is going to be how we do it with software defined access.
On the internet, if we have dozens or hundreds of routers running Lisp, then
this separation
is for the sake of scaling and I can create multiple of these databases to make
sure
that I scale out so that I don't get overwhelmed. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
that I scale out so that I don't get overwhelmed.
And lastly, Cisco doesn't actually believe that Lisp is going to take over the
entire internet.
It's going to take over pockets of the internet.
So I mentioned, maybe we've got dozens of routers in this space.
But if we only have dozens of routers in the space, that means we don't have
the rest of
the internet.
So we're going to have this outside world that isn't running Lisp.
In order for me to connect to the outside world, I'm going to need a router WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
In order for me to connect to the outside world, I'm going to need a router
that has that
connection.
And this is going to take the form of a proxy and we'll just say XTR.
Meaning that we have this router operating either as a PITR for when traffic is
coming into
the Lisp domain.
And we have a proxy egress tunneling router or a peter, I guess we could call
it.
But as the traffic is leaving the Lisp domain, this kind of gives us that thing WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
But as the traffic is leaving the Lisp domain, this kind of gives us that thing
we said we
can't have a sort of default route.
So if I bring a packet in and I'm destined for subnet W, I might check the
database and
it says, hey, I don't actually have an entry for W as a subnet as an endpoint
identifier.
So what do I do?
Do I just drop it at that point?
Well, no, that's exactly what the, in this case, the PTR is going to be all WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Well, no, that's exactly what the, in this case, the PTR is going to be all
about.
I forward the traffic, through the underlay, to get to the peter.
And then the peter is going to send it out into the outside world.
And likewise, again, when it comes back in, it'll take on the PITR form of
operation.
So these proxy XTRs, they're very important because they can connect us to this
outside
world, again, specifically it's not part of our Lisp domain. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
world, again, specifically it's not part of our Lisp domain.
So we don't know where something is.
We're going to assume it exists out there and we're going to send it to the
nearest proxy
external tunnel router.
So just some terminology, we probably need to make sure that we have coming out
of this
conversation.
And as we drill even deeper into Lisp in the next video, we're going to see how
a lot of
these concepts really start to come together.
But again, let's make sure that we have this terminology down and we know what
we're talking
about when we make a reference to the ETR or the ITR or the MR or the MS WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
about when we make a reference to the ETR or the ITR or the MR or the MS
because that's
going to be critical for us when we're talking about Lisp.