Now one of the first elements regarding a first hop or dnc protocol to provide
a fault tolerant
default gateway for a client is that you need to have at least two routers that
can support that client.
So in our example in our topology here let's go ahead and focus on PC12 as a
client device
that's connected to the switch port here on this multiplier switch or in this
example it's just
acting as a layer two switch and then I've got two routers router one and
router two that can act
as part of the first hop or dnc protocol and the fault tolerance. So let's take WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
as part of the first hop or dnc protocol and the fault tolerance. So let's take
a moment and
discuss how these routers on their respective gig zero zero interface and gig
one zero interface
can provide fault tolerance for a PC. So starting off the PC here has the ip
address of 10.12.0.51
with a 24 bit mask and its default gateways configured to be .99 on that same
network.
Now that PC could be statically configured with that ip address and default
gateway or it could
learn via DHCP but the end of the day if that client's default gateways .99 if
this PC is going to forward WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
this PC is going to forward
traffic to any other network other than the local 10.12.0 network it's going to
forward it to his
default gateway at .99. So for fault tolerance if we have two routers like
router one and router two
that can support first hop or dnc protocols there's three options that we can
choose from. One is a
proprietary protocol from Cisco called hsrp which is an acronym for Cisco's hot
standby router
protocol and here's how it works we configure the gig one zero interface here
on our two and the
gig zero zero interface here on router one and we specify that with hsrp we're WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
gig zero zero interface here on router one and we specify that with hsrp we're
going to have a
virtual ip address and for the purposes of this topology that virtual ip
address that they're both
going to support is giving me the default gateway address of 10.12.0.99 and
that way if one of these
two routers fails the other one is there to support that default gateway
address and vice versa.
Now behind the scenes with hsrp besides having a virtual ip address that's
supported by both of
these routers we're also going to have a virtualized mac address. Now the WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
these routers we're also going to have a virtualized mac address. Now the
actual mac address is associated
with this virtual ip address it depends on a few things number one are we using
hsrp version one
or we're using hsrp version two and regardless of those two there's also
another option that says
let's use the burn in address on the device acting as the active router
supporting the virtual ip
address but by default there's a specific mac address associated with version
one and a different
specific mac address that's used with version two and with hsrp we can set up h
srp group so we
would get that for example group one or group two or group three and as part of WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
would get that for example group one or group two or group three and as part of
the last character or
characters of the virtual mac address it's going to include that group number.
Now as these devices
are communicating back and forth they're also using multicast and the actual
address for that multicast
address for the back and forth is a communicating with each other and verify
the other person is there
meaning our one verifies that our two is still there and our two is verifying
that our one is still
there. That multicast is 224.0.0.0.0 and if we're using hsrp version one is two
if we're using hsrp
version two that could rest ends in one zero two. So if you want the two rout WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
version two that could rest ends in one zero two. So if you want the two rout
ers here on this
common ethernet segment to go ahead and support hsrp they both need to be
running version one or both
need to be running version two. There's also the concept of a priority and if
both of these
interfaces came up at the same time and they're trying to decide which one's
going to be
responsible for responding to the virtual mac address and also responding to
the virtual
IP address which is what the client is using on their default gateway the
priority is going to
determine which one wins. So by default the priority is 100 so if we want our
two to win we could
set our two to be a priority for example of 101 and we believe our one as a WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
set our two to be a priority for example of 101 and we believe our one as a
default priority of 100
and if these two interfaces came up at the same time router two would win
because it has the
higher priority. Now let's imagine that our one came up first it has a priority
of 100 and then
let's say a minute or two later we bring up interface gig one slash zero on our
two and it has a
higher priority by default with hsrp they don't preempt. Our two's not gonna
say hey my priorities
bigger and better so I should be the active router. However if we want to force
that to happen there's
also an option called preempt where basically says the router comes up with a WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
also an option called preempt where basically says the router comes up with a
higher priority it's
going to take over that responsibility and switch roles. So if we had a higher
priority here of 101
and a lower priority here of 100 gig one zero would be the active router that's
supporting the virtual
IP address and the virtual MAC address and the other interface here would be
the standby and you
can actually have two or three or four routers all in that common segment but
you have one active
one standby and the others are just waiting in the wings. It's also possible to
set up multiple
groups as well so for our demonstration and our discussion here we're just WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
groups as well so for our demonstration and our discussion here we're just
gonna use a single group.
So if the actual group number doesn't matter if you're using group one or group
10 or group 20
as long as you're using the same group on both interfaces on that common
segment. So let me go ahead
and clean that up a little bit and let's talk about yet another option for a
first hop redundancy
protocol and that one is not a proprietary one it is an open standard and that
is called vrrp and
that acronym stands for the virtual router redundancy protocol. And as I
mentioned it's an open WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
mentioned it's an open
standard so for running for example Cisco router and a non-sysco router but
they both support
vrrp we could use that as our first hop redundancy protocol. Now the way that v
rrp works is amazing
because it's virtually identical to how hsrp works. We have the concept of
priority so far two has
a priority of 101 and our one has a priority of 100 our two is going to be the
active router except
they don't call it the active router they call it the master and that master is
in charge of the
virtual IP address so the default gateway address would be dot 99 that's the WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
virtual IP address so the default gateway address would be dot 99 that's the
virtual IP address
and corresponding with that there also be a virtual MAC address associated with
vrp as well
that's mapped or associated with that dot 99 address. And so the master router
is going to be
responsible for responding to our requests for that address and responding with
the virtual MAC
address and then may responsible for actually providing that default gateway
function for the
benefit of the client. So if we clean this up a little bit and didn't use the
words active and
standby but instead we'll use the terms master and backup. So over here this
will be the master
responsible for responding to our requests for that dot 99 address and WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
responsible for responding to our requests for that dot 99 address and
responding back with the
appropriate layer two address associated with that default gateway address and
over here are one
and it's gig zero zero interface that would be the backup. And although there
is the option of
configuring preempt with vrp preempt is on by default. So what that means if we
have r2
with a priority of 101 and over here we have r1 it's gig zero zero interface
with a priority of 100
and we change this from 100 on r1 we set it to 102 for example preempt because WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
and we change this from 100 on r1 we set it to 102 for example preempt because
it's enabled by
default that would cause r1 then to become the master and r2 on its gig one
zero interface would
then become the backup. But both hsrp and brp are going to have that virtual ip
address for the
router and an associated layer two address and whichever device is the active
in the case of hsrp
or the master in the case of vrp is going to be responsible for responding to
our requests for
that virtual ip address as well as providing the default gateway functionality
for the client
regarding that dot 99. So let's clean that up just a little bit and let's talk WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
regarding that dot 99. So let's clean that up just a little bit and let's talk
about one other
fhrp and that is called GLBP and GLBP is an acronym for gateway load balancing
protocol just like that.
Now with GLBP we are going to have a virtual default gateway ip address and our
example here we're
going to use .99 again so it's going to be 10.12.0.99 that's going to be our
gateway address however
instead of just having one router do all the work it can actually load balance WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
the traffic
between the two routers that are supporting gateway load balancing protocol and
you could have
three or four or more routers all participating in that activity and here's how
it works one of the
routers the one of the highest priority is going to be the active virtual
gateway. So in our example
let's go ahead and use three routers let's say r1, r2 and r3 they're all
connected to a common
segment here and let's go ahead and say this is gig 0/1 this is gig 0/2 and WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
segment here and let's go ahead and say this is gig 0/1 this is gig 0/2 and
this is gig 0/3.
One of these routers the one with the highest priority is going to become the
active virtual gateway
and for the purposes of this example let's go ahead and say it's r1 that won
that role and then r2
and r3 if the active virtual gateway goes away they can have an election and
determine who
is going to take over that responsibility but for now let's imagine that r1 won
the election
it's the active virtual gateway now what exactly does that mean r1 gets to do
well the active virtual
gateway based on the message going back and forth in this common segment is
going to identify WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
going to identify
that there are three routers involved here itself and also r2 and r3 and it's
going to assign each
of those routers as an active virtual forwarder so it's going to be here here
and here meaning
all three routers have the ability to forward traffic to support that default
gateway address of 10.12.0.99
and to facilitate the load balancing the active virtual gateway is going to
give each of the
active virtual forwarders a virtualized MAC address so down here I'll put MAC
address
and let's see the MAC address here on r1 the virtual MAC address is 1010 and WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
and let's see the MAC address here on r1 the virtual MAC address is 1010 and
let's say for r2 the
virtual MAC address is 1020 and on r3 let's say it's 1030 and let's just say
that's the last four
characters of its hexadessimal represented MAC address and then to actually
make this picture
completely let me add some clients I'm going to go ahead and put client one and
I'll put down here
client two and put down here client three so r1 is the active virtual gateway
all three of them are
active virtual forwarders and in their role as the active virtual forwarder WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
active virtual forwarders and in their role as the active virtual forwarder
they've been assigned
from the active virtual gateway a virtualized MAC address they can use for that
purpose so here's
the magic when client one does an rp request looking for its layer two
addresses default gateway of 10.12.0.99
the active virtual gateway is going to respond back with one of the three
addresses so let's imagine
that client one when does rp request for its default gateway is responded back
to you by the active virtual
gateway with the MAC address any in 1010 that means that r1 would be providing
that functionality the
default gateway functionality for client one and then let's imagine client two WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
default gateway functionality for client one and then let's imagine client two
does an rp request for
its default gateway of 10.12.0.99 and the active virtual gateway hears that rp
request and responds
back for this time it responds back with the MAC address of 1020 or the MAC
address any in 1020 so
C2 client two believes oh the layer two address for the default gateway address
is when any in 1020
and as a result r2 would be processing that because that's the active virtual
forwarder that's
managing that virtualized MAC address of 1020 and then third let's imagine that WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
managing that virtualized MAC address of 1020 and then third let's imagine that
client three does an
rp request for 10.12.0.99 and the active virtual gateway hears that request and
responds back with
the layer two addresses of 10.30 and then client three thinks oh the layer two
address of my default
gateway is when any in 10.30 and as a result it'll be r3 that's actually doing
the forwarding for
client three's traffic and that's how we can do load balancing across two or
more
devices that are using the first hop redundancy protocol named GLBP where with
hsrp and vrp basically
on one given subnet it's going to be one router that's either the active or the WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
on one given subnet it's going to be one router that's either the active or the
master router
and the other router or routers are simply waiting for that active or the
master router to fail so they
can take over the responsibility but here with gateway load balancing protocol
we literally have
the ability to do load balancing and with waiting we can also set up
proportional load balancing so
we could have for example you know r1 get twice as much traffic as r2 and have
r3 get four times
just much traffic for example as r1 but by default if we're using round robin
and we have equal weights WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
and we have equal weights
it would be a round robin equal weighted distribution across all three of our
routers as part of gateway
load balancing protocol so now that we've taken a look at three options for
providing fault
tolerance here for pc12 with hsrp or vrp or with gateway load balancing
protocol in the next video
I'd like to start walking through the configuration of each of these and we'll
start off with hsrp
in the very next video. So I'll see you in that next video in just a moment.