Now, to ensure we're on the same exact sheet of music regarding why we would
use something
like OSPF to dynamically exchange routes, let's take a look at our existing top
ology
so far, which is right here.
So in our previous skill, we connected the tier zero gateway and more
specifically the
services router function on the tier zero gateway to this network segment right
here.
And that's my 192.168.1 network.
And we also verified the previous skill that we have basic connectivity from
our tier zero
gateway to this IP address right here of .1 on that 192.168.1 network. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
gateway to this IP address right here of .1 on that 192.168.1 network.
And just as a reminder here on this tier zero gateway, we are using edge one
and also edge
two and a logical interface of .62.
And then we said a virtual IP address of .60 on this 192.168.1 network.
So for any of those details regarding setting that up and getting that
connectivity to this
external segment right here, please feel free to check out that previous skill.
And let's imagine for a moment that this computer right here, VM1 wants to
communicate with
a web server out on the internet. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Let's go ahead and choose a Google DNS server out at eight .8 .8 .8.
Just as an example of a server in the treatable out on the internet.
Now if this client has .1 on the 1010 zero network as its default gateway, it
would
forward the packet destined for 8888 to the layer two address of this interface
here on
gateway A.
This gateway would look at the layer three destination address, make a
forwarding decision
to the next hop in the path, which would be the logical interface here on tier
zero gateway
zero.
And then for the tier zero gateway, I'm going to just go ahead and shut out WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And then for the tier zero gateway, I'm going to just go ahead and shut out
that we're doing
the distributed router services there as well as these services router services
for that
external connectivity provided by our tier zero gateway zero.
And then this router can forward that packet to the next hop at .1, assuming we
have all
the routes for that.
And then this router would forward to the next hop and then to the next hop
until finally
is delivered over to 8888.
Now for the return path, which I'll put in red here, it need be forward back to
this router
and then back to gateway zero and then down to gateway A and then down to the
client for
the return path. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
the return path.
So for that to work from an IP connectivity perspective, that presumes that we
have all
the correct routing in place.
So this device, which will go ahead and label as physical router, would need to
know that
to reach the 1010 zero network, it needs to forward down this direction to the
tier zero
gateway.
And then the tier zero gateway would forward down to gateway A who would then
deliver it
to VM one.
So as far as default routes go, whenever we connect a tier one to a tier zero,
automatically
at that same time when we link this tier one to the tier zero, it doesn't like
the injects
a default route to this gateway says, Hey, if you don't know how to forward WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
a default route to this gateway says, Hey, if you don't know how to forward
anything
more specifically in your routing table, just go ahead and forward it to the
tier zero gateway.
And the same thing for gateway B is going to have a default route to the tier
zero gateway.
Also in our previous skill, we set up a default route manually here on the
gateway zero.
We told it, Hey, if you don't have a better route and routing table, go ahead
and forward
it to dot one as your next top.
So we manually set that up.
However, what we did not walk through is the configuration of this router to
train it on
how to forward packets back to, for example, the 1010 zero network or the 1020 WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
how to forward packets back to, for example, the 1010 zero network or the 1020
zero network,
because if we want packets coming back in from the internet to go back down to
these
clients and these VMs, this external router needs to know how to forward in the
direction
of 1010 zero or 1020 zero using our tier zero gateway address as it's next up.
So our options for training our routed environments, whether they're NSX down
here or physical
environments up here, our options include setting up static routes and think of
a static
route like a specific configured instruction that you and I give to a router.
We tell, for example, this physical router, hey, you need to get to 1010 zero WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
We tell, for example, this physical router, hey, you need to get to 1010 zero
anything
forward it down here to this tier zero gateway address, which would be using
dot 60.
That's its virtual IP address for its interfaces connected to this segment or
to get to the
1020 zero network forward it to this gateway address.
Again, that'd be the tier zero gateway address on that common segment.
However, if we had another tier one router and we had another segment with
another subnet,
that also means we have to go back to this physical router.
And once again, add a static route to reach that 10, for example, let's say it WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And once again, add a static route to reach that 10, for example, let's say it
's 30 to
reach that new network, let's say it's 1030.
Again, that'd be another static route we have to add here.
So another and more convenient option for training networking devices on how to
forward
IP packets is to use a dynamic routing protocol.
So let me clear up a little bit of this.
And with dynamic routing protocols, if we're in the same dynamic routing
protocol, for
example, here as well as here, that allows these two devices, these two layer
three routers
to dynamically share information regarding what's reachable.
For example, this tier zero gateway could say, Hey, if you ever need to reach WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
For example, this tier zero gateway could say, Hey, if you ever need to reach
the 1010
network, go ahead and forward packets to me for that subnet or vice versa.
If we want this router right here to advertise a default route and say, Hey, if
you ever
need to get to anywhere and you don't have a more specific route in your router
table,
forward it to me.
So we could advertise specific subnets and or default routes back and forth.
And in the world of NSX, there's two options as we mentioned in the intro.
One is border gateway protocol, which will cover any separate skill.
And the other dynamic routing protocol is OSPF, which is an acronym for open WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And the other dynamic routing protocol is OSPF, which is an acronym for open
shortest
path first.
So if we're running OSPF here and here, and we have both of them configured.
Correctly, this router can dynamically learn how to reach the 1010 zero network
and the
1020 zero network.
And our tier zero gateway can also learn about reachability to other networks
that are being
advertised from this physical router.
So let's clean this up a little bit and talk about a few of the key components
regarding
this routing protocol called OSPF.
Now with the OSPF, there's a few different flavors.
There's OSPF version two, which is also just commonly called OSPF. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
There's OSPF version two, which is also just commonly called OSPF.
And that supports IP version four, and that's the flavor we're going to chat
and talk
about in this skill.
So regarding OSPF, let's go ahead and put a few routers in place.
I'll go ahead and put a few here and another set here and more down here.
So in a large environment, it's very likely we're going to have dozens, if not
more, logical
layer three routers.
And then we have our connectivity between those.
However, they're connected physically or logically.
And each of these lines represents an IP subnet. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And each of these lines represents an IP subnet.
And let me go ahead and number these routers as well.
And for Paul tolerance, let me also go ahead and put a segment right there too.
And not every router needs to be connected to another router.
So when we have some networks here, for example, VLANs that only have one
router interface
on them.
So at the end of the day, each of these lines represents an IP subnet,
including these down
here and all these interconnections as well.
And just for fun, let's also label a few of these subnets.
We'll make this 10.8 and 10.9 and 10.10 and 10.11 and 10.12. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
We'll make this 10.8 and 10.9 and 10.10 and 10.11 and 10.12.
So we can add a couple more zeros and a slash 24.
We'll call everything in this network topology a 24-bit network.
So the question might be, how does router six know about how to forward down to
the
10.8 network or the 10.12 network?
And the answer is if we're not going to use a dynamic routing protocol, we'd
have to have
static routes to say, hey, forward either to here or here or there.
However, with the dynamic routing protocol, we can have all these routers share
information
with each other.
So the language of love in the world of OSPF is called an LSA. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So the language of love in the world of OSPF is called an LSA.
And when you see the term LSA, I'd like you to think of it like a puzzle piece.
And although there are different types of LLCs that are used, the basic
component of
an LSA is information about the network.
So this router right here, router six, is directly connected to this network,
we'll
have 10.56 and we'll call this one 10.67 and we'll call this network segment
right here,
10.106.
So from the perspective of this router router six, it can send out link state
advertisements
or LSA's or puzzle pieces, if you will, to say, hey, I'm connected to these WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
or LSA's or puzzle pieces, if you will, to say, hey, I'm connected to these
three network
segments, the 10.56, the 10.67 and the 10.106.
Now not only is our six router six doing that and sending the information out,
but every
other router running OSPF is also sending out all the information it has about
as directly
connected networks.
And although there's more than just one type of LSA for this discussion, I'd
like you to
imagine that it's link state advertisements from all the routers that are being
advertised.
And these link state advertisements are being flooded or forwarded throughout
the entire WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
the entire
network.
So at the end of the day, this router right here, router eight, is going to
have received
a link state advertisement or multiple link state advertisements from router
six indicating
these three networks.
Now router eight is also receiving that same information from the perspective
of router
four, router two, and router one.
So at the end of the day, if every router has all the puzzle pieces about all
the directly
connected networks, it can go ahead and then map out based on any target
network, the best
path to use to forward in that direction. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
path to use to forward in that direction.
And that's why it's called open shortest path first.
It's going to use the best path based on his calculations, having all the
information,
having all the puzzle pieces.
Now, one of the challenges with those PFS that if we have a say 50 or 60 or 100
routers,
that's a lot of LSA's that every single router has to look at and processing
used to calculate.
So in large environments, let me clean this up just a little bit.
Instead of having all the routers participate and have to process all the LSA's
from all
the other routers, well, we can use, we can actually group these routers into WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
the other routers, well, we can use, we can actually group these routers into
what are
known as OSPF areas.
So let's go ahead and put these three routers in an area called area zero.
And maybe we put these routers over here in an area called area one.
And then these routers over here, we put in an area called area two labels of
area
to each one of those.
And that way, only the routers in the same area have to listen to and process
all the
links they'd advertisements from the other routers in that same area. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
links they'd advertisements from the other routers in that same area.
So instead of having 12 routers worth of LSA's being advertised and propagated
across every
single router in the entire domain, now we reduced it.
So we have these four routers here that only have to listen to and process each
other's
LSA's area two also over here.
We have five routers that have to listen to and process each other's.
And up here in this area, we only have three.
So here for area zero, I'm going to redraw this just a little bit and I'm going
to draw
it like this because what really happens in the world of OSPF is that the
actual network WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
actual network
interfaces are members of an area and not the entire router itself.
So in this case, we have both interfaces on router one, included in area zero.
This interface here on router two included in area zero and this one as well.
And then they can share LSA's with each other.
And then for area one, router two has a couple interfaces included in area one
and our three
over here has one interface included as part of area two.
And that's important because we do need some connectivity between the areas.
So in this case, our three would be the link, if you will, between area zero WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So in this case, our three would be the link, if you will, between area zero
and area two.
And they have a fancy term for this type of device which is connected to two
areas and
they call it an area border router.
And that would also be the case over here with R2.
It would also be an area border router or ABR.
So even though if we have large environments with lots of routers, we can carve
them up
into multiple areas most of the time in smaller networks war in the case where
we have for
example, these three routers and we're connecting to one or two external WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
example, these three routers and we're connecting to one or two external
resources here or one
or two external physical routers or firewalls.
We probably could get away with just a single area for OSPF.
And when we do that, we're going to be using area zero and area zero, which can
be written
as a zero, depending on the vendor or zero dot zero dot zero, zero, zero, zero,
either
way is great.
That is also known as the backbone area.
So unless there's dozens or more of routers that are running and participating
in OSPF,
it's very likely we're going to have one single area called area zero.
And then when we configure our routers, we'll specify which interfaces are WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And then when we configure our routers, we'll specify which interfaces are
going to participate
in area zero.
So in our topology, it looks something like this.
We would go ahead and have the physical router or routers with their interfaces
participating
in area zero.
And then our tier zero interfaces, which are connected to that same segment, we
would
enable them with OSPF as well, specify that they're in area zero and away we go
.
Also here, I included a representation of our edge nodes because anytime we're
using
services such as connectivity to the external network, like we're doing right
here, we're
actually using the services of one or more of our edge nodes. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
actually using the services of one or more of our edge nodes.
So edge one is providing the address of dot 61 and edge two is the address of
dot 62 on
this tier zero gateway.
And then we also have a virtual address of dot 60.
So in our case, what we really have is a very small grouping or number of
routers that are
going to be running OSPF.
So very likely we'd just be using OSPF area zero as a single area OSPF
implementation.
And the benefit of that is we can share routes regarding the 10.10 zero network
from our
tier zero gateway to the physical router or to the physical device. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
tier zero gateway to the physical router or to the physical device.
It could be a firewall that's doing layer three routing either way is great.
And we could also advertise reachability information to the 10 dot 20 network
as well.
And if the external router was configured for it, it could advertise to us a
default route
to say, Hey, here's how you get to everywhere else.
If you don't have a more specific route in your routing table.
So let me clean some of this up and let's talk about a few other really
important aspects
regarding open shortest path first.
Let's imagine this represents this segment right there. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Let's imagine this represents this segment right there.
And my network that's the 192 168 one network with a 24 bit mask.
And in our previous skill, we set up basic connectivity to that network segment
.
So let's imagine this represents our tier zero gateway right here.
I'll just call it tier zero, which is this guy right here.
And behind the scenes, when we're doing that external connectivity, that tier
zero gateway
is going to be using the services router function for that bridge, if you will,
from the NSX
routed environment down here to that physical segment.
And then I'll go ahead and draw this router up here as well. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And then I'll go ahead and draw this router up here as well.
So there's our router connected.
I'll draw the little icon that represents this is a router or has a layer three
routing
function.
And just for grants, I'd like to add one other routing device up here.
We'll connect it as well.
So I'll draw the icons here for the routing function.
And for IP addressing, let's imagine this one's at dot one.
And let's imagine this router has the address of dot 136.
And for this T zero gateway, it has the virtual IP address of dot 60.
And behind the scenes that virtual IP address of dot 60 is being supported by
this pair WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
this pair
of edge nodes, which is edge one at dot 61 edge to a dot 62, which we
configured in
a previous skill.
And I know [garbled] network segment right here to the color that's here, which is
white.
So I'll go ahead and put that in right here.
Fantastic.
And there's our network segment and I'll label it as well 192 168 dot 1.0.
There's our network segment with a 24 bit mask that we're using there.
Fantastic.
All right.
So we configured all three of these devices to run OSPF in order to share WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So we configured all three of these devices to run OSPF in order to share
information
back and forth with each other.
For example, about the networks down here being shared with the top router and
the router
up here sharing the default router other routing information.
In order for that information to be shared, we have to have what's known as a
full adjacency.
Think of a full adjacency like being on really good terms with a neighbor where
like you'll
share anything and talk to that neighbor.
It's all good.
This is what we need in OSPF is a full adjacency in order to share routing
information.
And not only do we have a full adjacency, but it's also referred to as being a WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And not only do we have a full adjacency, but it's also referred to as being a
fully
adjacent neighbor.
And now I have some good news and some bad news.
The good news is is that on most appliances and most devices that run OSPF, if
we use the
defaults most of the time, all the parameters are going to agree.
And as a result, they can become OSPF neighbors, establish a full adjacency and
start sharing
information, routing information with each other.
However, oftentimes, especially when we're dealing with two different vendors
that might
have slightly different values, if one of those parameters is not correct and WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
have slightly different values, if one of those parameters is not correct and
doesn't
agree with the other side, for example, this router has a setting of A and this
one has
a setting of B for some parameter in OSPF that could prevent them from getting
into a full
adjacency and becoming fully adjacent neighbors.
So I have an acronym I'd like to share with you that can help you remember a
few of the
key things that have to be in agreement for two OSPF neighbors to become fully
adjacent.
And they are stamp.
And I'm going to go ahead and put a little extra T there.
Let me explain what these are.
The S is for the same network. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
The S is for the same network.
If this router here, I'll go ahead and label this as R1 and we'll label this as
T0, which
it already is.
So if R1 and T0 for their connections to this common network, if R1 believes it
's the 192.168.2
network and the T0 gateway believes it's the 192.168.4 network, that is going
to
cause them to not agree on what that common network segment is.
And as a result, they won't become fully adjacent neighbors.
So here I'll say same IP net for the same IP subnet, which means the same IP
network
or subnet. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
or subnet.
Another thing they have to agree on is the timers.
So periodically with OSPF, we're going to be sending out little hello messages.
So if this router router one thinks that it should send out hello messages
every 11 seconds
and our T0 gateway thinks it should send out hello messages every 12 seconds.
If they don't agree on those timers, they won't become neighbors.
So let me remove those and let's talk about the other T here.
They also need to agree on the OSPF network type.
So in OSPF, if we have ethernet, it's going to be using an OSPF network type of WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So in OSPF, if we have ethernet, it's going to be using an OSPF network type of
broadcast.
And the OSPF network type of broadcast, and I'll add net there for network type
, simply
means that we can see and find each other via multicast on this common ethernet
segment.
So by default, if we're configuring routers and they're connected to ethernet
segments,
the default network type is going to be broadcast.
However, if it's different on one vendor versus another one, that could prevent
them
from becoming neighbors.
All right, let me clean that up a little bit.
And the next one down here is the area.
So if our one on this interface here thought, oh, this is area one. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So if our one on this interface here thought, oh, this is area one.
And over here on our T0 gateway, it thought that this interface was connected
to area
51 or area zero, if they don't match, that will prevent them from becoming
neighbors.
They have to agree on all of these properties.
Another gotcha that often happens with multi layer switches is the MTU isn't
the same.
So here for the routed interface on each of these logical devices, here we have
our
tier zero gateway.
And here we have our external router.
If the MTU, the maximum transmission unit for IP routing is set to, for example WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
If the MTU, the maximum transmission unit for IP routing is set to, for example
, 1504
here and it's set to 1506 here, that information is communicated back and forth
in the low messages.
So if it doesn't match up, if it's not the same, that could prevent them from
becoming
neighbors.
So this MTU is just for the routed logical interface.
It's not applicable to our logical layer two switching or distributed switches,
which
most likely we're going to be using jumble frames there anyway.
But from an OSPF perspective, from the routed interfaces, they both have to WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
But from an OSPF perspective, from the routed interfaces, they both have to
agree on the
same MTU if they want to become neighbors.
So let me clean that up a little bit.
And then the last one right here is authentication.
And you might say Keith, it says P there.
That's because they wanted the the mnemonic to work.
So so the P actually is for password, but in OSPF, they refer to it as the
method for
authentication.
So if we're using a certain type of password up here on our one, whether the
type or the
actual string of text is different than the one used down here on our T zero
gateway,
once again, that would prevent them from becoming neighbors.
And again, this will be super useful when we're doing troubleshooting of why, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And again, this will be super useful when we're doing troubleshooting of why,
why is my NSX
environment not setting up a full adjacent neighborhood with my external router
?
Because at that point, we want to go through this list and see what's different
on the
two ends.
All right, so I clean that up a little bit.
And let me talk about one last concept here before we go to the next video for
a game
plan.
And that last concept on a common network segment like this, ethernet segment
here, we're
getting a OSPF is that we are going to have a DR and I apologize that it's the
same exact
acronym as we have for a distributed router. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
acronym as we have for a distributed router.
But in the case of OSPF, I'll draw a line here, in the case of OSPF, a
designated router,
which is the DR in OSPF, has certain responsibilities on that network segment.
And we only need one of them for the basic function regarding OSPF on that
network segment.
And for fault tolerance, we're also going to have what's called a backup
designated router
in case the primary or first designated router is no longer available.
So we're going to have one DR on an ethernet segment and one backup designated
router on WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
router on
that same ethernet segment.
So let's imagine that this is the DR right here and this is the BDR.
And let me use this color right here for full adjacency.
So when we see this, we'll realize that means a full adjacency.
So the DR and BDR are assuming everything's correct here are going to form a
full adjacency
with each other, meaning they can share routes back and forth and communicate
with each other.
That's great.
And every other router other than the DR and BDR is also going to form a full
adjacency,
but they're going to form a full adjacency with the DR and also with the BDR. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
but they're going to form a full adjacency with the DR and also with the BDR.
And the benefit of having the full adjacency with both is because if the
designated router
goes away or has a problem, it's already got a connection to the BDR and can
start using
that BDR and its routing services as part of OSPF.
However, what we don't need is we don't need a third designated router.
So the third device on the network here is going to be called a DR other,
meaning it's
not a DR, it's not a BDR, but it's a DR other.
And then just for grands, let's bring a fourth device to this topology. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And then just for grands, let's bring a fourth device to this topology.
We'll put it right here.
We'll call this R4.
So it would also establish a full adjacency between it and the DR and the BDR
as such.
And this would also be a DR other.
So here's the designated router.
Here's the backup designated router.
This is a DR other and this is a DR other.
And then for the relationship between these two DR others, they are going to be
in what's
called a two-way state.
And the short story there is that as two OSPF devices on the same network
segment are discovering
each other and then forming their formal adjacency, they're going to go through WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
each other and then forming their formal adjacency, they're going to go through
a whole bunch
of states, including the init and the two-way state and something called X-star
to an exchange.
I'll just put an EX for that before they go into a full adjacency.
However, these routers are not going to bother going through the full formal
adjacency with
each other because they already have adjacencies with the DR on the network
segment and the
BDR on the network segment.
Well, they would go ahead and they would form all the way up to the two-way
state and that's
where they would park and say, you know what, we really don't need a full adjac
ency here
because we've got our full adjacencies with the DR and BDR respectively. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
because we've got our full adjacencies with the DR and BDR respectively.
So in this topology here, these two devices, T0 and R4, they both are DR others
because
there was already a DR and BDR present.
However, in the world of NSX, our tier zero gateways do not want to take on the
responsibility
or the role of being the designated router for a segment.
So they have their priority effectively set to zero for that DR/BDR function.
And even if we only have one router like we do right here, it's going to be the WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And even if we only have one router like we do right here, it's going to be the
DR, this
tier zero gateway as it connects to that segment and then builds an OSPF
neighborhood with
the DR, it's not going to act as a BDR.
It's going to stay in the state of a DR other and just maintain its full adjac
ency with this
DR.
And then if another router shows up that's willing to take on a responsibility
as a DR
or BDR and it becomes the BDR, it's at this point.
This T0 gateway is going to establish the second full adjacency to that BDR.
But again, just for the heads up, when we're setting up OSPF and we're
leveraging these
edge nodes, the edge nodes that are providing this external connectivity WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
edge nodes, the edge nodes that are providing this external connectivity
function, they
are not going to by default be a DR or BDR on this segment.
So now that we've taken a look at some of the details regarding OSPF
specifically for
IPV4, that's OSPF version two.
In the next video, let's take our existing topology and let's put a specific
game plan
in place for the implementation and verification of OSPF.
So I'll see you in the next video in just a moment.