As we move down the stack, we are now going to talk about the distribution
layer.
The distribution layer purpose is right there in the name.
It's to distribute.
It's to communicate out to the access layer in this case.
We have a core block and a distribution block.
And again, even though we like to logically connect these like so, we know that
there's
really a pair of switches here and we might fully mesh those.
But when we look at the access layer and we'll be talking a lot more detail WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
But when we look at the access layer and we'll be talking a lot more detail
about the
access layer here coming up, there are a lot of switches down here.
And so the distribution layer needs to make sure that it's communicating with
all of those
access layer switches.
So let's talk about what features are going to be required in order to make
sure that
a distribution switch can properly serve in the role of being in the
distribution block.
First and foremost, we need to make sure that we have layer three switches in
this role. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
this role.
The reason for that is as we described before, there's going to be a dividing
line here,
where we have layer three upstream and layer two downstream.
Now this does assume layer two at the access layer and that is usually what we
're going
to see in the real world.
It's very common for us to have layer two extended out there outside of layer
three
access layer deployments as well as fabrics like SD access.
So we'll stay focused on layer two being pushed out to the access layer and WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So we'll stay focused on layer two being pushed out to the access layer and
address layer
three later on here in this course.
So we understand that we're going to have layer three upstream layer two
downstream.
And so we need to make sure that we do support the proper routing protocols.
Although interestingly, we don't actually have to support much in the way of
routing.
As if we think about it, the distribution layer is not sitting here in the
middle.
The core is going to have all of the connections going everywhere, which means WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
The core is going to have all of the connections going everywhere, which means
it needs to take
routes in and send routes down to the distribution layer.
So at that point, we really only have a single path up from a layer three
perspective.
This one path can easily be turned into either a default route or have a
significant number
of summarized routes.
And so this is going to be a topic of conversation as far as how to perform
routing.
So the distribution, again, this is for distribution switches now from a WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So the distribution, again, this is for distribution switches now from a
distribution switch perspective,
we can be pretty content oftentimes by configuring it as a layer three stub.
Now this looks different between EIG, European, OSPF.
Stub from an EIG RP perspective is a node EIG RP.
Here we go.
It's a node configuration.
But from an OSPF perspective, it needs to be an area.
And so we need to make sure it fits into the routing topology, whether it's EIG WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And so we need to make sure it fits into the routing topology, whether it's EIG
RP or
OSPF.
But yeah, we don't actually need to worry too much about a complex layer three
configuration
here.
We just need to get a routing protocol spun up and be able to integrate with
the core
from that perspective.
So from here, let's go ahead and talk a little bit about port count, which
should sound familiar.
Ultimately, port counts going to be a requirement at every layer.
I know we just talked about it at the core layer, but it is going to matter WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
I know we just talked about it at the core layer, but it is going to matter
here as well.
We need to make sure that we have enough connections to connect to all of the
access layer
switches.
So not just port count, but also port type.
We spent enough time talking about that in the last video that we probably get
a sense
of that here.
The difference is that we probably have less bandwidth requirements and less
throughput
requirements on distribution switches.
So we don't have to worry as much about bandwidth or about packets per second,
although we do
still need to make sure that it has enough to handle the situation. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
still need to make sure that it has enough to handle the situation.
But this is relative to our core switching requirements.
Now next, we need to think about what configurations go on the distribution
switch.
And there's going to be quite a few that we need to talk about.
And this is where with the core switch, our conversation was very short.
We didn't have to talk about much in the way of configuration because we didn't
have a
lot of concerns there. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
lot of concerns there.
But here with our distribution switch, we're going to need to make sure that we
configure
our switch virtual interfaces, which is the fancy acronym for VLAN interfaces.
These SVIs are going to be the gateways for our VLANs.
This is a very important role of the distribution layer and the distribution
switches because
as our hosts down here, that's a laptop, connects up into the network, it's
going to need to
get off of its subnet. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
get off of its subnet.
It's going to have to find its default gateway and that's going to be an SVI
here that
draws a dot on the distribution switch.
Well, this host might be in VLAN 10 and we might have dozens of VLANs.
We might have 20 and 30 and 35 and 41 and that's a random list of VLAN IDs.
But that alone says that we need five different SVIs on the distribution switch
and again,
we might have dozens more.
So we need to make sure that we're supporting those SVIs. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So we need to make sure that we're supporting those SVIs.
Now the SVIs must be redundant and the way we establish and achieve redundancy
on VLAN
interfaces and specifically on gateways would be via a first hop or done to see
protocol.
Now there are many FHRP's out there.
We're going to be talking about those in this course as well.
But we typically in a Cisco environment like to think about the hot standby
router protocol
or HSRP and then from an industry standard perspective, we might see the WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
or HSRP and then from an industry standard perspective, we might see the
virtual router.
There we go.
Virtual router redundancy protocol or VRRP and then we might also want to talk
about global
load balancing protocol or GLBP, which is another Cisco protocol.
Now usually we're talking about one of these ones in the front.
GLBP doesn't get used a whole lot these days.
But regardless of which one we're talking about, we do need to support the FHRP
's.
Furthermore, we might have a host down here that's in VLAN 20 and we don't want WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Furthermore, we might have a host down here that's in VLAN 20 and we don't want
those
hosts to be able to communicate.
Well talking about security and the ability for us to control who can talk to
whom, this
is the concept of access control.
Now this can get very difficult to manage at a global scale.
But within the context of a distribution block, we might actually be able to
wrap our
arms around it.
And the way we do that is by deploying access control lists to our SVIs. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And the way we do that is by deploying access control lists to our SVIs.
And so this is going to give us security enforcement at the distribution level.
Now this doesn't help us to prevent communication between let's say two hosts
on VLAN 10.
Because if we're staying on VLAN 10, we're not passing through an SVI and
therefore the
access control list never actually gets to block the traffic.
But it can help us with VLAN to VLAN access control and that's something we've WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
But it can help us with VLAN to VLAN access control and that's something we've
been doing
for quite a while on our networks.
Now another important configuration is going to involve spanning tree protocol.
Again, for better or worse, we're running layer two downstream.
We are going to need STP involved.
Now we should always be running some form of rapid STP these days.
That's either going to be Cisco's flavor, rapid PVST or technically rapid PVST
plus or
multi instant spanning tree or multiple spanning tree. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
multi instant spanning tree or multiple spanning tree.
That's what we call these days, which is MST.
So we're going to want to make sure we have the proper STP version running, but
we also
need to consider STP roots and topologies.
We want to make sure that we are maximizing the efficiency of our links.
And because we have two distributions, which is we're going to want to make
sure that we split
the root configurations between distribution switch one and distribution switch WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
the root configurations between distribution switch one and distribution switch
two and
establish at least a pair of topologies in the environment, which again
increases the
efficiency of what we want to do here.
Now lastly, there is one more configuration that I wanted to point out and this
actually
has to do with our routing protocols up here.
So we mentioned that we might be running a stub environment.
So if we're running a stub environment, one of the best things we can do is to WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So if we're running a stub environment, one of the best things we can do is to
perform route
summarization.
The idea of route summarization, if I can squeeze it in there, there we go.
Route summarization is saying that I want to take a bunch of subnets like 10.0.
0.0/24
and then we'll just list off a few others here, dot 1.0, dot 2.0, dot 3.0.
And so if all of these are slash 24's, then we could combine this all into a WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And so if all of these are slash 24's, then we could combine this all into a
single route
that is 10.0.0, 10.0, dot 0, there we go, slash 22.
This summarized route is basically saying, hey, rather than advertising for
routes, I will
advertise a single route.
Now how big of a difference this may because dependent on the size of the
network.
If we have dozens of distribution blocks and each distribution block has dozens WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
If we have dozens of distribution blocks and each distribution block has dozens
of SVIs,
each one of these routes or subnets would belong to an individual local VLAN
for example.
Well, at that point we could make a massive difference in the routing table
size on the
core.
We want to take the routing table and reduce it as much as possible because
that will help
it perform that fast layer 3 switching.
So this is a way the distribution block can help the core block get the job WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So this is a way the distribution block can help the core block get the job
done.
If it has fewer routes to sift through, when it's performing its routing table
lookups,
then it will be a much faster switch.
So route summarization is a very important part of distribution blocks.
Now if our routes are very pretty like this where they go in a straight order
and we can
easily summarize them, then that's going to make for a better conversation than
if we
have routes that are all over subnets that are kind of all over the place. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
have routes that are all over subnets that are kind of all over the place.
And so when it comes to good network design, we might want to make sure that as
much as
possible, we are performing the distribution of subnets in such a way that they
can be
summarized upstream to the network core.