First, top redundancy protocols are a critical part of adding redundancy to our
network.
This is specifically going to help us out with our default gateways.
The fault gateways are how we get off our subnet.
If we have a user down here and they're part of the 10.100.1.0/24 subnet, let's
say they
have an IP address of .100, then they're going to need to get to other subnets
via the
default gateway. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
default gateway.
Now, these days, in our modern networks, we're going to do that with multi-lay
er switches.
We're going to have an SVI here.
That'd be a switched virtual interface or a VLAN interface.
Let's say that this is VLAN 100.
We're going to call this layer to segment VLAN 100.
We create an SVI for VLAN 100.
That'd be the interface of VLAN 100 configuration command.
We add an IP address to it. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
We add an IP address to it.
As our default gateway, this device knows that it's default gateway is .254.
It can get that via DHCP.
It knows how to get off the subnet.
Now, we have a way to route to other networks.
Let's say that I have another SVI here.
This is for VLAN 200.
This has its own network segment with another endpoint over here.
Let's just actually say that this is a printer. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Let's just actually say that this is a printer.
We're trying to print something off and it's on VLAN 200.
This is 10.200.0/24, and then we'll add an IP address here of .50.
How do we get there?
This host is going to perform an ARP or the default gateway.
This is going to matter for how we accomplish everything with first-hopper-d
ensity protocols.
ARP is going to play a big role. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
ARP is going to play a big role.
Either way, we're going to ARP.254.
We're going to find it here on our yellow subnet.
This SVI is part of the subnet.
It can respond at layer 2.
It says, "Hey, here I am."
Then our device is going to send a packet over to the printer.
The way it really works is it gets forwarded up layer 2 to the SVI and VLAN 100
.
We perform a routing operation internally to get from SVI or maybe able to say WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
We perform a routing operation internally to get from SVI or maybe able to say
VLAN 100
interface to the VLAN 200 interface.
We can perform a local forwarding operation down to the printer.
The reverse traffic flow would look very similar.
The default gateway is naturally a very important part of our network.
If it were to go down for any reason, because network failures do occur, well,
at this point,
we would not be able to communicate between our different subnets.
The redundancy of a gateway is going to be mission critical. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
The redundancy of a gateway is going to be mission critical.
The network industry could have evolved in different ways.
We could have just had another gateway over here and it's maybe .253.
Maybe we could have added multiple default gateways down here to the host.
That's not how we did it.
Instead, we said, "We're going to lock in on a single default gateway."
We're going to rely on the network to perform the redundancy.
How exactly do we go about doing this? WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
How exactly do we go about doing this?
Again, this is where first hop redundancy protocols come into play.
If we break down the name, we're talking about a first hop in here.
That's what the FH stands for.
This would be our first hop, our default gateway, to get off of the network.
Then redundancy protocol probably speaks for itself.
We need to have a redundant default gateway out there on the network.
How do we do this?
We know that the default gateway is locked to .254. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
We know that the default gateway is locked to .254.
What we want to do is we want to create the concept of a virtual IP address.
This virtual IP address is going to be shared between our nodes.
.254 is actually going to become sort of this IP address that either one of
these devices
is capable of running at the same time.
Now if we're using this as a virtual IP address, we probably want to change the WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Now if we're using this as a virtual IP address, we probably want to change the
physical
address of the first device to let's say just be .252.
Can I ping .252?
Can I ping .253?
The answer is yes, I can ping both of those.
They're both responding to those IP addresses.
By the way, that device on the right would be also adding this to our VLAN 100
interface.
Just to be clear.
Those IP addresses are active, but so is the virtual IP address. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Those IP addresses are active, but so is the virtual IP address.
It's going to be managed by the concept of the active node.
The active node runs the virtual IP address until it can't anymore until it
goes offline.
Then we introduce the concept of the failover.
The failover node will run if the active node goes down.
The active node goes down and then the failover node manages the virtual IP WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
The active node goes down and then the failover node manages the virtual IP
address.
Importantly, we can't just survive on a virtual IP address.
This virtual IP address also is going to need a virtual MAC address.
This is the glue that holds all of this together because all of this
communication here to get
up to the SVI, even a shared virtual IP address.
This is all layer 2, which means that we're dealing with MAC addresses.
I never know from this host on the left to this host on the right, I never WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
I never know from this host on the left to this host on the right, I never
learn the other
hosts MAC address because it's on a completely different network segment.
Instead I'm going to learn the MAC address of my default gateway, which used to
be right
here physically, but now it's up here virtually.
If I'm going to communicate, as we mentioned, using by arping for .254, then I
'm going
to need to learn the MAC address, which is going to have to also be shared. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
to need to learn the MAC address, which is going to have to also be shared.
It's going to be shared by our two nodes and it's going to map to the virtual
IP address.
Everything is in steady state operation and one of these nodes is in charge.
Let's say that our active node is here on the left.
Then all of a sudden there's some kind of failure.
This node goes down and we're going to find that the failover node takes over
for .254.
Even though we don't have the lines drawn on here, we do have a network path to WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Even though we don't have the lines drawn on here, we do have a network path to
this other
device.
Because we take over for the virtual IP address and the virtual MAC address,
now this device
takes over and it can run as .254, this host down here never knew there was a
failure
because we fail over so quickly to the new node.
Then we have to have a conversation about what happens now when the active node
comes
back online. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
back online.
This is an interesting concept as well.
We have the concept of preemption to help us address this, which is basically
our failback.
The question of whether we want to perform a failback.
If the active node is on the left and it experiences a failure and now the
active node is on the
right, but then this node comes back online, do we want to fail back or are we
content
just to let this node run as the active until it experiences a failure. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
just to let this node run as the active until it experiences a failure.
We'll see as we look at HSRP and VRRP and these different FHRP's, the different
protocols
that we can deploy, that preemption is going to be a topic of conversation.
It actually is going to be very important when we get into deeper FHRP designs,
but we
need to be aware that this concept does exist.
If I have preemption enabled on the active, then once it goes down, we have WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
If I have preemption enabled on the active, then once it goes down, we have
active over
here now running and we come back online, well at that point we're going to pre
empt the
other device and we're going to come back to being the active node.
Does this matter from a user perspective?
Does it ever know that all of this is happening?
No, the endpoints that exist on our network, they are completely oblivious to
all of this.
This is known as a network level of redundancy, but network is handling this. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
This is known as a network level of redundancy, but network is handling this.
We don't have to worry about configuring our endpoints to deal with any of this
.
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