So with HSRP, Hot Standby Router Protocol, always remember for the exam we're using a Cisco proprietary protocol.
So if the scenario is ever about having two multi-layer switches or two routers and they're different vendors, then HSRP is not what you're going to use.
It's not going to be your answer. It's going to be VRRP in that particular case.
So with HSRP now, what do we do?
We are going to be creating groups for each and every single one of our subnets slash VLAN slash broadcast domains that we have.
And we're going to be creating these. In this case, since it's multi-layer switches, we're going to be creating these groups on SVIs.
So I'd go to, for example, interface VLAN 10 and do my configuration.
All right. When we do the configuration and we set it up, for example, on this SVI and this SVI, we're going to get one active router for that group.
One active router for that group. That is going to be the router with the highest priority.
So this is based on priority. And the active router is going to be the one forwarding packets.
It's going to be the one responding to ARP requests.
It's also going to be sending and receiving hellos because it has to let the other routers in the group know that it is the active router.
You got one standby router in your group.
This is the router with the second highest priority amongst the routers in that group.
It's going to send and receive hello packets.
So that way there it can receive and learn about the active router.
But it's also going to send because it wants the active router to know that it exists.
But if there are other routers in the group because you can have more than two routers,
you can have basically an unlimited number of routers in your group with HSRP.
So, for example, you had three, four, five or six routers at the distribution layer for that,
something which typically you want is typically only two.
But if you had more and they were all interconnected, let's say we had another one here and it's connected up.
It's connected up over here. It's connected up down here. It's connected up down here.
Then, yeah, you can have all three in the group if you wanted to.
So the standby router has to inform all the other ones.
That's why it sends hellos as well.
So it can inform the other routers in the group that, hey, I am a standby router.
And it waits for the active router to fail so it can become the active router.
And then if you do have extra routers, like I said, that are part of that group,
then they're going to be what we call listeners.
So they're not active. They're not standby.
They're listeners because they're just listening for hello packets.
Why? Because they want to know if there's already an active device.
If there is, okay, then it looks for a standby device.
Is there a standby device? Okay, yeah, then I'm just going to continue listening.
So if all of a sudden the active device fails, the standby becomes active,
and then a listener can become standby.
So we have to go through different states in order to figure out who's active,
who's standby, who's listener.
Typically, you're only going to have active and standby.
You'll never have listeners.
But all the routers in the group, where they have two or more,
are going to have to go through something called the listening state
at some point in time, especially when they're initializing.
So when we look here, in this particular case,
we've got these different states listed.
So obviously, if you're an active state, that means you're the active router.
If you're in the standby state, you're the standby router.
But when you initially enable this process, or if there's a failover that happens,
the routers are going to have to go through different states.
Now, if your standby failure happens, you immediately go active.
You don't have to go back to the beginning and start over.
But if I bring you up for the very first time as a router,
or you've been rebooted, or anything like that,
then you go to the initial state.
It's the state as the start.
It's when you've been configured for HSRP,
or the interface has just been brought up, as an example.
What if you bounce the interface, the SVI?
You're in the initial state.
From there, you go to the listening state.
So you don't speak first.
You listen first.
You know the virtual router IP.
You know the virtual router IP address because you've been configured with it.
Therefore, you know the virtual router MAC address as well
because it's automatically generated based on the fact you configured the IP address.
So you're listening to see if there's anybody else out there already
that is active or standby.
If there's already an active standby device there,
you stay in the listening state.
But if there is no active or standby device out there,
meaning you're not receiving hello packets,
then you're going to move to the speak state.
Now, if there's only an active device,
then you're going to move to the speak state
because you have a chance to become standby.
But if there's an active and standby,
you stay in the listening state.
If there's nobody that's speaking right now,
then you know that you have a chance to become active.
So you're going to go speak.
So what does speak mean?
Now you're going to send your own hello messages.
And you're going to actively participate in the election process
of the active and standby router.
So if you're the only one,
then you're going to promote yourself to being active.
If there's an active one there that's already active,
depending on how you're configured,
you might become active or you might go standby.
So it all depends on the configuration you have,
whether you move on or not,
from standby to active and so on and so forth.
So in the speaking state, you're doing your election.
If you're standby, you become standby.
If you determine you're active, you're active.
So definitely make sure you understand these states
and their definitions for the certification exam
in case there's a drag and drop on the exam about all of these,
or in case you have to answer a multiple choice question about these.
Just want to make sure you're prepared.
All right, let's go ahead and do some configurations now.
And we're going to do it in our live environment.
So I'm going to leave this diagram up so we can see it,
but I'm going to do the exact config that you see there live.
So first of all, let's go see PC number one.
All right, PC number one right now.
We'll see if we type in IP config.
We'll see that PC number one.
Let's try this again.
I don't want this at the bottom.
There you go.
All right, so PC number one, 10.0.0.10, 255.255.255.0.
With a default gateway of 10.0.0.254.
So this is going to be the address we are going to use
for HSRP in this particular case.
So right now, let's go to DSW1.
We'll type in configure terminal.
And we're going to type in interface VLAN 10.
And the commands for HSRP are standby.
So there's a lot of different options we can have here.
We're definitely going to not cover all of them,
but we're going to focus on the ones we need to know
for the certification exam.
But one thing you want to know here is that
the group number does not have to be entered.
If you don't enter the group number,
it defaults to zero.
I repeat that.
If you don't configure the group number,
it defaults to zero.
Why is that important?
Because if you are on the exam,
and you have to configure HSRP
according to their instructions,
if you forget the group number,
you configure it for zero by accident.
It doesn't give you an error.
It automatically does it for group zero.
And the last thing you want to do is do an entire config.
And for you, it's working fine.
But in the end, when the system grades it,
you use the wrong group number.
And guess what?
You get zero.
That's not what you want to have happen.
So be careful with that.
So the group number can be anything you want it to be.
It doesn't have to match your VLAN.
It doesn't have to match your subnet.
It can be anything you want it to be.
From zero to 255.
So I'm going to use 10.
Just because I want to.
And it has nothing to do with this being interface VLAN 10.
It has nothing to do with this going to be part of my VLAN 10 subnet.
No, I'm just using it because I want to.
On the exam,
they don't tell you what group number to use.
And you can use whatever you want.
But if they tell you a group number to use,
make sure you use it.
If they tell you a group number to use,
make sure you use that group number.
Now, maybe also remember this.
The group number has to match.
So if they already have one device configured,
and they're asking you to do the other device,
what does that mean?
You're going to have to verify the group number on the other device.
And maybe even the IP address.
What if they don't give you any details,
and you have to find them on the other device?
So you're going to be looking for the IP.
You're going to be looking for that group number.
All those things have to match in this config.
Now, once I type in my group number,
I am then going to type in IP,
because this is the most fundamental command you need to get it turned on.
Standby, then the group number, then the word IP.
And then you put the IP address in that you want to use.
So remember this IP address we had here?
That's the IP address we're giving to the PC.
So what did we say we were using on our PC?
We said we were using 10.0.0.254.
So that's the one we want.
10.0.0.254.
That's it, done.
Hit enter.
So that is like the basic command.
That's it, that's all.
Now, is it going to work the way I want it to work,
the way I like it to work?
No, because there's a lot more I have to teach you,
and a lot more that's going to be on the certification exam
when it comes to HSRP.
So right now it's going through the states,
the states that we talked about a while ago.
So right now it's more than likely in the speak state,
and now it's in the active state.
So I am the active device.
Now, if we type in do show IP, no, do show standby,
we'll see here that for, be careful with this,
interface VLAN10.
That's what that means.
That's the interface name and number.
Because if we were doing this on a router interface,
it would actually have the router interface listed there,
like gigabitethernet00.
So that doesn't mean VLAN10.
That means interface VLAN10.
We are part of group 10 because of this command right here.
And the virtual IP address is 10.0.0.0.254
because we typed in this command here.
It says that I am the active device,
and we can confirm that with this syslog message right here.
What else?
There is the virtual MAC address.
The virtual MAC address.
And so how was this generated?
This is going to be important for you.
So we have 0.0.0.0.0C07AC08.
That's the MAC address.
How was this determined?
Well, this is Cisco's OUI.
So that was given to Cisco by the IEEE.
For use as what?
MAC addressing.
OUI, Organizational Unique Identifier for MAC addressing.
All right?
07AC means HSRP version number one.
0A, this is your group number.
Group number.
That is the group number.
In what?
Hexadecimal.
So notice how this is the exact same MAC address that is right there.
Why?
HSRP version number one.
And it's what?
Group number 10.
So how does that group number come about?
Well, if you don't know how hex works, every single hex character is four binary bits.
So 0, for example, would equal what?
0.0.0.0.
And A, well, if you remember, hex goes from 0 to 9 and then A, B, C, D, E, F.
Well, A is equal to what?
A is equal to 10.
So what is A in binary?
Well, if it's 10, if you remember 128, 64, 32, 16, 8, 4, 2, 1 from your CCNA days,
we are just dealing with these four right now.
So 10 would be 8 plus 2, and there you go.
So now when you combine it all together, what do you have?
You have 0, 0, 0, 0, 1, 0, 1, 0.
Okay, what does all of that equal?
All of that equals 10.
So let's say we had group 20.
What would group 20 be?
Okay, well, the best way to do that right now to test it is let's type in interface VLAN 20,
and let's say standby 20, and we are in 2.
All right, now let's take a look at do show standby again,
and you'll see where this can get very, okay.
Right now it's still going through the election process, but we'll grab that right there.
So it's 14.
It's 14.
So let me write that out for all of us, or I'll just erase this stuff here.
All right, and I'll show you how to calculate that one.
So 14.
So you got to be careful with this, because if I asked you right now which group is this,
which group is this, if you say 14, you are wrong.
Right, Conrad?
If you say 14, you're wrong.
Right, Conrad?
Conrad says memorizing all the virtual MAC addresses for the first hopper density protocol is the most annoying part of CCNA.
Exactly, right, and that's the struggle.
We're going to get tested on that here in Encore as well.
So 14 is what?
Well, 1 equals 0001.
4 equals 0100.
Now put it all together.
You get 0001, 0100.
Now figure out what they are.
So you'd have 128, 64, 32, 16.
So we have 16 plus 8.
Oh, 4, 16, 8, 4, 2.
I'm looking at it.
I'm like, that doesn't make sense.
There you go, 20.
20.
Group 20.
One more, just to show you.
We have interface VLAN 50, right?
Let's say you're group 50.
It ends in 32 now.
So look, group 50 is actually 32.
So again, which group is this?
It's not group 32.
You've got to be mindful of that, right?
We're dealing with virtual MAC addresses.
It's not group 32.
You've got to be mindful of that, right?
We're dealing with which group?
Well, you're going to have to take the first value of 3.
That's going to be 0011.
And then you have 2, which is 0010.
Now put them together, 0011, 0010.
So you've got 128, 64.
You've got 32, 16, and 2.
So that's 48 plus 2 is 50.
There you go.
So yes, is this something you might want to be able to do?
Sure, because if you can do the simple math,
then that means you'll always get those questions right.
So that's how the MAC address is created.
It's just dynamically generated using Cisco's OUI, 07AC,
and then the group number that you created.
So as you've seen so far, we have created groups for VLAN,
for interface VLAN 50.
We've created groups for interface VLAN 60.
And as you've seen so far, we have created groups for VLAN,
for interface VLAN 50, interface VLAN 20,
and interface VLAN 10.
Now, let's go to ASW1 right now.
You're welcome, Conrad.
Let's go to ASW1 right now, because remember what we said.
When you become active, you're going to send out what?
What is it called?
A GARP, a gratuitous ARP.
So let's take a look at our MAC address.
What do we see?
07AC in here right now.
There it is.
So there's the one for VLAN 20, AC14, right?
It ended in 14, we said.
We should have one for VLAN 10 here.
There it is.
There's the one for VLAN 10.
We said it ended in 0A.
And then we should have the other one that we just did for VLAN 50,
AC32.
There it is right there.
Now, here's a prime example of suboptimal routing
or suboptimal switching.
So right now for VLAN 10, DSW1 is the root bridge for VLAN 10,
and it's also my active forwarder because we configured on DSW1.
So notice in this output, gigabit 1 slash 0 slash 45 to get there.
That makes perfect sense.
What I want to point out to you right now, though, is, for example, this one.
This right now is the active forwarder.
It's the default gateway, but this is the root bridge.
This is the root bridge right now for VLAN 20.
Look what port it's sending it out of.
Why?
Because this is the root port right now for VLAN 20.
So now the traffic actually for VLAN 20 would go bloop, bloop, bloop, bloop,
which I said you don't want to do, right?
That's why it's so important.
You're seeing it right here now, live,
that if you're not mindful of how traffic flows with Spanning Tree Protocol,
you could have suboptimal forwarding based on other things you've configured.
So now the question is, do we modify Spanning Tree Protocol,
or do I make this one the active forwarder for VLAN 20?
More than likely, depending on my environment, I might have VLAN 10 going this way,
20 going this way, maybe 200 going this way, maybe 50 going this way.
It depends on what you want.
Just make sure you configure it properly based on how you want traffic to flow.
You need to be in control, and that's Spanning Tree Protocol, right?
Now what does that mean?
It means if we go to our PC again, we should be able to see in our ARP cache 10.0.0.254,
and there it is, and there's the MAC address.
So at some point, PC1 sent out an ARP request,
and DSW1 responded back with the reply, and it gave me my MAC address.
So let's go ahead and do a ping.
Let's ping to the default gateway.
And you'll see that I'm getting a response from who?
That's going to be from PC number one.
Sorry, DSW1.
DSW1 is the one who's responding back to me because it is the active forwarder.
Let's ping somewhere else in the environment.
Let's see.
Could I do 8.8.8.8?
That is because I probably don't have one of my routers set up properly.
Let's go to branch right now.
What's the IP address?
10.50.12.
10.50.12.129.
Let's use that address because I'm pretty sure I can reach that one right now.
10.50.12.129.
There you go.
All right, so but the question is, is who am I going through?
One of the greatest ways we can test that is do a trace to that address.
So, if we do 10.50.12.129, we'll see from the response which router we're actually going through.
So, if I can see here 10.0.0.1, then I know I'm going through DSW1.
So, that's how you can confirm it in the real world and on the certification exam.
Is HSRP working the way I want it to?
Is VRRP working the way I want it to?
Is GLPV working?
Use a trace to any address beyond because then you'll see what default gateway you're going through.
All right, let's go ahead now and set up DSW2 for interface VLAN10 because we've only done one so far, right?
So, interface VLAN10, let's now type in standby.
And what's our group?
Our group number we said for this one was group 10.
And what's our IP?
10.0.0.254.
And it's so important that you get the numbers matching 100%.
If they don't match 100% between DSW1 and DSW2 for interfaces that are in the exact same subnet, then it's not going to work.
So, things to pay attention to on the exam are what?
Are the group numbers the same on the interfaces in the same subnet?
Are the IP addresses the same on the interfaces in the same subnet?
So, interface VLAN10 and interface VLAN10.
So, what does that mean?
Could Cisco also accidentally give you a scenario or a question where it's interface VLAN10 here, but interface VLAN20 here,
and they put the wrong IP address and the wrong group number or the right IP address and the right group number on different interfaces?
Yeah, they could do that.
And you've got to recognize that that's not going to work.
It's got to be two interfaces in the same subnet.
So, interface VLAN10, interface VLAN10 are in the same subnet.
But if they did interface VLAN10, interface VLAN20, and then put that addressing information on it, there's your problem.
Now, you shouldn't be able to, let me check, you shouldn't be able to give it an IP address that's not in its actual subnet.
You see?
It says right there you can't do that.
But does that stop Cisco from doing copying and pasting and a little bit of Photoshopping and a multiple choice question to see if you understand that it has to be an interface in the same subnet?
It has to be the same group number.
It has to be.
No, it doesn't stop them, right, from Photoshopping.
So, always be mindful of that.
Even though we know certain things could never happen in the real world, it doesn't stop Cisco from Photoshopping.
All right.
So, I got the interfaces in the same subnet, and I have the same group number, and I've got the same IP address.
Now, something to keep in mind here is that I already have an active device right now.
I already have an active device right now.
So, we are having an election right now.
And notice I went standby.
So, how does the election process actually work?
What decided that that was active?
What decided that that was standby?
So, here's how the election process works.
Number one, it's based on priority.
So, if I type in do show standby, what is my priority?
My priority is 100 on DSW2.
Let's go to DSW1.
Do show standby.
What is my priority for interface VLAN10?
It is 100.
So, whoever has the higher priority becomes the active router.
Well, our priority is tied.
Our priority is tied.
So, what breaks the tie?
The tie is going to be broken by the device, or the tie is going to be broken with the higher interface IP address.
Meaning that whoever has the higher interface IP address becomes the active forwarder.
So, DSW2 has the IP address 10.0.0.2, and DSW1 has the IP address 10.0.0.1.
Which one's higher, DSW2 or DSW1?
Chat in.
Not sure what question.
Yep, it's DSW2.
So, DSW2 has the higher IP address, so it should be the active device.
And we can see in our output that DSW1 is active and DSW2 is standby.
So, basically what I just told you is true, but my devices are calling me a liar.
What I just told you is true.
Higher priority, and if the priors are tied, then the higher IP address is the winner.
Well, not according to my devices.
Why?
Because by default we are non-preemptive.
You'll see here that it says preemption is disabled.
What does that mean?
It means that if someone is already active, they remain active no matter what.
So, even if DSW2 has a higher priority, it doesn't matter.
If DSW1's already active, it stays active.
Even if DSW2 has a higher IP address, doesn't matter.
If DSW1's already active, it stays active because it's non-preemptive.
HSRP by default.
So, if you want to be able to control who is always the active forwarder under normal operating conditions, you will have to turn preemption on.
So, for example, if right now we force a failure.
So, let's just say interface VLAN10.
Let's just shut down interface VLAN10 just really quickly.
That's going to cause a failover to happen.
So, we should see DSW2 is going to become active for interface VLAN10 or group 10, I should say.
You can see it's now active.
And if we want to test that with our PC, if we just simply do a trace, we'll see that we're now going through DSW2.
That's perfect.
There you go.
DSW2 10.0.0.2.
But now, if we go back to DSW1 and we re-enable it, is DSW1 going to become active or is it going to go to standby?
Okay.
Well, because preemption is off, we will go standby because there's already somebody who's active.
That's what it means.
If preemption is disabled, like it is, you can see it right there.
If preemption is disabled, it means that if somebody's already active, you cannot become active, no matter what, even if you have a higher priority.
So, you can see I'm standby now.
So, even if I said standby 10 priority, let's change the priority to 110 on DSW1.
And we'll look at the output of do show standby right now.
We'll see here that I have a priority of 110 and DSW2 has a priority of 100.
It doesn't matter.
Why?
Preemption.
Preemption says what?
Preemption says DSW2's active.
It will remain active until it fails.
DSW2's active.
It will remain active until it fails.
So, how can I turn around and force DSW1 to always be, always be the active device under normal conditions?
Well, one, give it a higher priority like we already have done.
And two, turn on preemption.
So, standby 10 preempt.
Done.
Now, because I have the higher priority and preemption is enabled, I become the active device.
Three really important commands you need to know for the exam.
Oh, and by the way, if you accidentally type standby preempt and you forgot the 10, guess what that would configure it for?
Right?
If you accidentally did this, you see?
So, if you accidentally forgot the 10 on the exam, then you would actually be configuring it for zero and it would not actually work.
Right?
So, make sure you don't forget the group number.
So, from a personal experience, folks, preemption should always be on, no matter what.
Because momentarily, we're going to show you some additional failover features with HSRP.
And the only way they're going to work is if preemption is on anyways.
I have always believed it should be something that is on, but I feel like they have it off by default so they can make the exam harder.
So, I am going to turn it on over here as well.
Standby 10.
And that is not a joke.
I'm serious, all right?
Because the odds of them testing you on preemption is going to be high.
Why?
It's been that way for years.
Years.
So, here is the standby device.
So, I'm forcing, right?
I'm forcing DSW-2 to be standby.
I'm forcing DSW-1 to be active.
So, here's a good starting standby configuration.
Here's a good starting active configuration.
Just keep that in mind.
So, remember, if priority is not listed, it means your priority is 100.
So, here, priority is not listed.
It's 100.
Priority is listed.
It's not 100.
All right.
So, let's go ahead now and do a continuous ping on our PC.
Got too many mice here.
I'm grabbing the wrong mouse.
All right.
So, let's do a continuous ping.
To 10.50.12.129.
Forget how to do a continuous ping here.
There you go.
Minus 10.
Perfect.
All right.
So, we have the ping going, and it's got a timeout value of not timeout, but every two seconds.
One, two.
Yeah, every two seconds.
Right?
All right.
So, we'll let that run.
Now, what we're going to do is we are going to go to DSW1, and then we're going to just
type an interface range gigabit Ethernet 1 slash 0 slash 17 through 24.
Let's just go ahead and shut down all these interfaces.
And what we're going to do is we're just going to go over to the PC, and we're going to see
how many packets go missing.
Not too bad.
I mean, what?
Failover happened in my case relatively quickly.
Only lost a packet or two, maybe.
Obviously, your end stations would be transmitting a significantly greater number of packets
in a two-second timeframe, but, you know, that's a nice failover using just default
timers.
And we can definitely get it quicker.
Now, let's bring all these interfaces back up, and we'll see if we type in no shut.
And we'll just come back here.
So, I lost one failing back over as well.
So, that would have been what?
Spanning sheet protocol having to converge potentially.
And during that convergence, one of the packets just simply didn't make it through when it
was all said and done.
But there you go.
There is an example of being able to failover from one device to another device in your
default gateway, and your client only has to worry about being configured with one of
All right.
Let's just take a peek at some of our slides now.
So, our slides, I do have the configs for you if you ever want to go back and review
them.
That's DSW2's config.
And then we've already seen this output here so far.
So, we understand the MAC address.
We understand the virtual IP now.
We understand preemption enabled versus disabled.
We know who's active.
We know who's standby.
So, we've got you covered there so far.
So, let's talk about failover now.
So, right now, the scenario I provided to you is based on what?
It's based on DSW1 and DSW2 being able to communicate with each other inside the subnet
VLAN broadcast domain.
So, DSW1 and DSW2 are sending hello packets back and forth in that environment to each
other using the multicast address 224002 for HSRP version 1.
And they're doing that every three seconds with a dead timer of ten seconds by default.
And we can verify those timers in our config.
If we type in do show standby, you'll see the default timers are three and ten.
So, if all of a sudden something happens to DSW1, then that means there will no longer
be the hello packet coming from DSW1.
So, DSW2 within ten seconds will recognize that and promote itself to active.
And as we talked about, send out the GARP and everything else in our previous discussion.
So, now traffic flows this way.
So, that's what I just demoed to you.
That's what is happening.
So, it's the absence of hello packets that are causing the failover to occur because
of the failure.
So, the failure of the SVI or the failure of the physical interfaces.
So, as long as one physical interface is still up that has the ability to send hello packets,
technically DSW1 would still remain active, right?
Yeah.
So, it's just simply based on the fact that hello packets cease to exist.
And then when DSW1 recovers, let's not forget we gave it a higher priority.
Let's not forget we turned on preemption, and therefore it becomes active again.
So, if we didn't have preemption turned on and we didn't have a higher priority, then
DSW2 would remain active instead.
So, based on our configuration, this is what happens when we fail back.
But what we need to realize is that the default behavior of HSRP is purely based on those
hello packets.
Do I hear you or not, says the standby device.
And if the standby device hears the active device, then the standby device remains active.
If it doesn't hear the active device, then what's it going to do?
It's going to promote itself to being active.
But what if there's a failure over here somewhere?
For example, what if gigabit 1 size 0 slash 13 fails or 1 size 0 slash 14 fails?
Are the hello packets, folks, still going to be going back and forth here?
Yeah.
Which means that if both these interfaces go down, traffic's going to be sent here only
to be dropped because that device cannot send it.
Ah.
So, we need in our production environments to make sure that we are not only concerned
about a failure here somewhere, we're also concerned about failures upstream.
For example, with our directly connected interfaces.
So, the directly connected routed ports in our particular scenario, the routed ports
of 13 and 14, we have the ability to turn on what is called HSRP interface tracking.
And there's two different ways we can do this depending on the model of iOS you have and
the device you have.
So, for example, what we're using in our demo environment does it one way, but I have a
bunch of switches here that do it a completely different way.
And so, I'm going to teach you both ways today in case either or shows up on the exam.
I want you to be prepared for it.
So, the whole point here is that if, for example, an interface fails, I want to be able to tell
this device that it should go active.
That's what I'm trying to accomplish here.
So, let me repeat that.
If, let's say, an interface fails, I want to tell this device to go active.
How can we do that?
Well, the easiest way to do that is to lower our priority.
If I lower my priority, if I lower my priority, then that forces DSW2 to go active.
So, let me show you how you can do it right within HSRP.
Now, my demo devices, like I said, don't support this method, but I have four switches right
over there that do.
And you could either see this option or the other option I'm going to show you momentarily
on the certification exam.
So, in this scenario here, I am in interface configuration mode, interface VLAN 10.
Look what I type in standby, the group number, the word track, and then the interface I want
to keep track of.
So, what does this state?
It states, if the interface is up-up, don't do anything.
Let me repeat that.
If the interface is up-up, don't do anything.
If the interface is any other scenario other than up-up, like up-down, down-down, administratively
down-down.
If it's any of those options, lower my priority by, in this case, 250.
So, if the interface is not up-up, lower my priority by 250.
So, you can put any number you want there.
That makes sense.
So, let's just consider our scenario right now.
What's the current priority, folks, of DSW-1?
Current priority of DSW-1 is 110.
What is the current priority of DSW-2?
It is 100.
So, let's say Gigabit Ethernet 1 slash 0 slash 13 fails.
What is the minimum decrement value we need to get DSW-2 to take over?
What is the minimum decrement value we need to get to in order for DSW-2 to take over?
Well, if DSW-2 is 100, what do I have to lower this to?
I would have to lower this to 99, right?
Okay.
So, as Conrad said, 11.
What's 110 minus 11?
99.
So, we could literally just type in 11 here.
And now, if Gigabit 13 fails, we minus 11 from 110.
We get 99.
So, my next hello packet that comes says 99.
This device goes, oh, I better take over.
Boom.
It becomes active.
And we're good to go.
It's not bad.
Now, let me teach you a little something else here.
Do we really have to decrement, folks, fully?
Let me rephrase this.
Let me rephrase that.
Do we really need DSW-2 to take over if only Gigabit 13 fails?
What do you think?
Not really, right?
Because of what?
Because of this interface here.
We still have another path to go, right?
So, we don't necessarily need that.
So, this might not be the best option for you.
What if we split it up?
What if we said if one or the other fails?
Okay, if one or the other fails, we'll just decrement a bit.
Like, let's do this instead.
Let's add another command.
So, I'm going to type in standby 10 track Gigabit Ethernet 1 slash 0 slash 14.
But in this case, let's do something like this.
Let's do 7 and 7.
So, what does that mean?
It means that if we have this scenario where Gig 1 slash 0 slash 13 fails, we subtract 7.
What does that equal, 103?
Are we still active in this scenario, yes or no?
Yeah, of course we're still active, right?
We still are higher than this.
Okay.
So, let's say we have this failure, minus 7 now, 103.
Again, we're still active, right?
So, imagine a scenario where you said, hey, you want to make sure that you only fail over to DSW2 if both of those links fail.
Ha, ha, ha.
Ha, ha, ha, ha, ha, ha.
Right?
Split it up somehow.
Now, if both fail, now what's that number?
110 minus 14.
96, is it?
I think my math can be pretty bad.
But you get the picture, right?
You get the picture now.
Now, we have a failover as soon as both those interfaces fail.
So, that's something to keep in mind for the exam.
You can have multiple standby commands for multiple different purposes.
Let's not forget, too, okay?
Let's be clear about this, too.
Remember how I said failure this way is based on hellos, right?
Okay, well, what if this happens?
What if this fails, this fails, this fails, this fails, but these four interfaces are still up and running?
Are we still getting hellos back and forth?
Are we still getting hellos?
Yeah, of course we are.
But this doesn't make sense now, right?
Because traffic's going to end up doing this.
I don't want that to happen.
So, maybe what we do is we also track these two interfaces as well.
So, track gigabit ethernet 1 slash 0 slash 21 and gigabit ethernet 1 slash 0 slash 22.
And if both of those interfaces fail, then I want to lower my priority.
Because even though the hello packet's still going back and forth, right, now all of a sudden we've got suboptimal traffic forwarding.
Because traffic might do something like this, or traffic might do something like that.
We don't want that.
So, always think, too, that just because it's based on hellos in here.
Well, what if those two primary interfaces that are directly connected to ASW1 fail?
Well, I don't want to be the default gateway then.
Because that doesn't make sense from a traffic standpoint.
So, I should track those ones as well and decrement them.
So, it's not just about decrementing these interfaces.
It's also about decrementing those in those oddball scenarios.
Right.
So, that is an example using the command that is right on the interface to accomplish your objective.
Right.
However, my switches right now don't do that.
Yes, you can track port channels.
You can track.
Yes, absolutely.
So, you can track port channels.
So, this device, if I go to interface VLAN10 and we say standby 10 track, you'll see I can't put in the interface number at all.
Can't put in the interface name.
Can't put in the interface number at all.
So, how do we do it on this type of platform then?
So, in this case, you need to create what is called a tracking object.
Okay.
So, I'm going to show you how to create a tracking object instead.
So, we're going to do the same scenario, but we're going to do a tracking object instead.
So, let me back out of this config.
Let me go here.
And how do you create a tracking object?
You type in track, and then you give it a number.
So, let's just type in track 1 for today.
Now, what do I want to track?
I want to track the status of my interface.
And what interface do I want to track?
I want to track gigabit ethernet 1.0.0.13.
And what do I want to track about it?
I want to track its line protocol, meaning are you up or are you down?
All right.
Let's do the same thing now for we'll create another tracking object, a totally different one,
but we'll create it for gigabit 1.0.0.14.
Now, we'll go back to interface VLAN 10.
And what we'll type in is standby 10 track 1.
And now I put in my decrement value.
What do I want to decrement it by?
I want to decrement it by, we said, for example, 7.
Let's do the same thing for tracking object number 2.
So, tracking object 1 is keeping track of this.
Tracking object 2 is keeping track of that.
So, it's really the same thing, except I can't use the interfaces right in this command on this iOS version and platform.
But I get the same result in the end.
All right.
So, now I want to type in show track.
And you're going to see we have two different tracking objects.
We have a tracking object 1 for gigabit 1.0.0.13 and a tracking object 2 for gigabit 1.
And it says it's up.
Why?
Because the interface is up.
And you'll see that we have attached it to HSRP interface VLAN 10 group 10.
Now, if I type in show standby, we're going to see for interface VLAN 10, our priority is 1.10.
It is configured in our running config as 1.10.
And right now, it is 1.10.
And we are going to use these tracking objects to keep track of everything.
So, let's go ahead and bring down one of our interfaces and see how this changes.
So, we'll type in configure terminal interface gigabit ethernet 1.0.0.13.
Let's shut that down.
And you'll see here that the tracking object goes down.
So, since the tracking object has gone down, what does that mean?
Well, let's type in do show track first to show you that, yes, it has gone down.
Why?
Because I shut it down.
And now, if we look at the output of do show standby, what are we going to see?
We're going to see that our priority is now 1.03.
So, it is configured as 1.10, but now it's 1.03.
So, you're seeing why the number shows up twice.
The number shows up twice to show you what you've configured it as,
and then the other number is what it actually is.
Okay.
So, that's what.
Now, let's go ahead and bring down 14.
So, go do show standby now.
And you'll see here that we are now priority of 96,
which means DSW2 should now have promoted itself to active.
Look, I'm in speak state right now.
So, I've demoted myself.
DSW2 is now active, and DSW1 should promote itself here very shortly to standby.
And there you go.
It has.
Right?
Question coming in.
If track is the same thing as doing it on the interface, then which would be best to use?
Oh, okay.
So, you must have missed what I had said about that.
All right.
So, as I was explaining a while ago, if your device supports the interface option, right,
then you can go ahead and use that.
Use the interface option that I gave the whole explanation of right here.
Okay?
Fine.
If that is available, do it that way.
Okay?
If it's not available on your platform, then you have to do it this way.
So, it could show up either or on the certification exam.
Right?
And that's why I'm showing both methods, just in case.
For the longest time, I always did it this way, always did it this way, always did it this way.
And then all of a sudden, I had a platform with an operator.
I'm like, what?
Why is that not available?
And I had to start doing it this way on those devices.
All right.
So, just that way, there you know.
There's the two options.
All right.
And this option doesn't even exist for VRRP, by the way.
You can only do it this way with VRRP.
You cannot do it this way.
All right.
So, there you go.
That is this cool little feature in action.
So, interface, range, gigabit ethernet, one slash zero slash 13 and 14.
No.
All right.
That's three to 14, but that's okay.
All right.
We're back up.
We're good to go.
All right.
And therefore, I should promote myself to active, and I did right there.
You can see.
Why?
Because I have the higher priority.
All right.
But there's more.
There's more.
I sound like one of those late night infomercials.
But wait.
There's more.
Because we have to consider some other types of scenarios.
And when I say other types of scenarios, I'm talking about scenarios where the failure
could be further in our environment somewhere.
It could be way further in our environment.
And so, for example, if under normal conditions, we always go this way, but all of a sudden,
this interface went down, and we wanted to make sure that if this went down, we went
this way instead.
How could we do that?
Well, that's where you need to use something like IPSLA.
How many of you have used IPSLA before on a Cisco device?
Yeah.
Right.
There's many different things you can do with IPSLA.
Many different things you can do with IPSLA.
Right.
So, for example, you can use IPSLA to send a simple ping.
A simple ping to test connectivity.
Are you there, or are you not there?
If you're there, awesome.
If you're not there, blah.
And then we can have something occur.
Right.
When it comes to IPSLA, it's going to be covered for you in the additional videos.
So, for example, under management protocols and services for Encore version 1.1, so after
day eight, you still have other videos to remember to watch, I have an IPSLA configuration
and verification video right there that you can utilize.
And that will teach you some aspects of IPSLA.
It's a massive feature.
It's a massive tool that is available on Cisco devices.
For example, like I said, you can send a ping, and then based on the ping being successful
or not, have your router do something on that.
You can even test, for example, round-trip times.
So, let's say you have a WAN connection, and you want to keep an eye on the WAN connection
over your service provider.
What is the one-way delay?
What is one-way jitter?
What is one-way values?
Why?
Because maybe you want to make sure you're getting what you're paying for.
And then also, what are the return values between that device?
So, that's what IPSLA can do for you.
So, for example, I'll give you a quick demo here, because demos are always fun.
Let's go ahead on DSW1 and generate a probe.
So, let me get the IP address, show IP interface brief.
So, it's that IP address right there we are going to ping.
So, that was R1's outside interface.
So, I'll create something like this, IPSLA, and then I give it a number.
So, I can reference that number.
So, this is probe number one.
And you'll see here, there are many different types of probes I can create.
Depending on the platform, you'll have more probes or less probes.
But this is the IP address.
You'll have more probes or less probes.
But this is the ICMP echo probe, meaning ping.
So, I'm going to do an ICMP echo.
What's the destination?
We said the destination was going to be this particular IP address right there.
So, I'll plug that in.
And then from what source?
So, what source?
We'll do source interface gigabit ethernet 1.0.0.13.
So, pinging out there, pinging out there to that IP address on the other side.
And we're going to do that, let's say, every five seconds.
Every five seconds.
Now what we're going to do is we're going to set up a schedule.
So, IPSLA schedule.
And there's many different ways that you can schedule your IPSLA instances.
So, I talk about that in the IPSLA discussion.
But I'm going to schedule it for IPSLA 1, which is the one we just created.
Right?
We just created IPSLA 1.
So, that's what I'm going to schedule now.
And I can schedule it to age out.
I can set a life for it.
I can make it recurring.
I can start it, for example.
At a certain time of the day.
Well, I want to start it now.
As soon as I hit enter, I want it to start now in this particular example.
And how long do I want it to last for?
What's its lifetime?
Well, in this case, I'm going to allow it to last forever.
So, I just want this ping to start now and happen every five seconds until I
manually shut it off.
So, now if I type in do show IPSLA statistics,
you're going to see here that I have three pings so far.
That returned an okay.
It means when I ping there, I got a response back.
I ping there, I got a response back.
And you'll see it's now up to six.
So, let's just go ahead and shut down that interface.
And what we should see here is that eventually we start getting an error
message.
And there you go.
Time out.
And now it's one.
Okay?
So, this is just the probe.
The probe is doing the probe.
That's it.
Nothing else.
Okay, that's all it is.
In this case, it's a probe.
That's what SLA is for, to set up probes, to set up artificial traffic,
to set up, like if I wanted to check to see what the numerical statistics are
from here to there for voiceover IP.
I could create a fake voiceover IP packet, same size, same shape,
same QOS markings.
And then I can measure the information, delay, round trip, jitter.
That's what you can do with this.
Tons of stuff you can do.
All right, so now I'm just going to bring up the interface so that way
there we start having successes again.
All right?
So, we should see here everything should be coming back to normal real
soon.
Uh-oh.
Why is the ping not working?
It should be working.
Why is the interface not running?
Nothing better than live demos.
Okay, so it's up, up.
There you go.
I'm just impatient.
That's my problem.
All right.
So, we're good.
So, now what we have to think about is this is going to be for HSRP example.
So, what do I need now?
I need a tracking object.
So, let's create a tracking object.
Call it track three.
And we're going to track IP.
We're going to track SLA.
We are going to track entry number one that we created.
And what are we just wanting to track?
The state of it.
That's it.
Just the state of it.
Nothing else.
What does that mean?
It means if your state is okay, my tracking object is up.
If your state is time out, then my tracking object goes down.
So, let's type in do show track.
And what do we have now?
We can now see that we are tracking the SLA instance.
So, if it's okay, go back up here.
If it's okay, then my tracking object is up.
If it's not okay, meaning it's time out, then my tracking object goes down.
So, let me test that for you.
We'll shut down that interface.
Right?
And it just doesn't have to be the interface.
It's can I no longer ping that IP address?
Because if I can no longer ping that IP address,
then my tracking object goes down for whatever reason.
Right?
So, now the tracking object is down, as you can see.
So, we look at the tracking object.
It now says it's down.
All right.
Cool.
Let's bring that back up.
And while that's coming up, let's now show you how to apply this to HSRP.
So, for HSRP, what we're going to do is we are going to now type in
interface VLAN 10, and we'll type in standby for group 10, track,
and what object is that?
Tracking object number three.
And what are we going to do?
We're going to decrement our priority.
Let's say, in this case, let's decrement it by 110 for fun.
Now, let's just make sure we're back up here.
That looks good.
Now, if the tracking object is not back up yet, which it's not back up,
you're going to see we're going to fail over.
Yeah.
You see how we failed over?
Because the tracking object hasn't come back up yet.
But we're failing over.
DSW2 is now active because the tracking object is down.
But, look, the tracking object went back up, and now we're active again.
Right?
So, we've attached it.
Do show standby.
And if you go down, you'll see that we have three tracking objects now.
So, this one is tracking object number three.
Tracking object number three is tracking what?
The status of IPSLA, whether it's the ping's good or the ping's not good.
So, the ping's good.
Tracking object's up.
My priority's 110.
Ping's bad.
Tracking object's down.
Therefore, my priority gets decremented by 110.
So, let's go ahead and bring down that IP address now.
And we'll see that the ping's going to fail.
When the ping fails, what's going to happen?
Ping fails.
Tracking object goes down.
DSW2 goes active.
Bam.
And notice I've done all of this on DSW1.
But because I'm decrementing my priority,
DSW2 through the hello package is going to know what to do.
So, if you look here, my priority's actually zero.
Why?
Because the tracking object's down.
So, this is something you have to be able to read yourself, too,
on the potential exam folks.
Right?
For example, if you look in here and it says,
Priority zero, configured 10.
Priority zero, configured 110.
And they ask you, why is your priority zero right now?
Well, the priority's zero because tracking object three is down.
But that might not be one of the options, right?
It might be based on the fact that, yes, tracking object three is down,
but then you need to show track.
Show track says, okay, we're monitoring IPSLA.
And so, we type in do show IPSLA statistics.
And what do we see?
Timeout.
And then you look at the answer options.
The answer options say IPSLA process ID one,
or IPSLA instance one is timeout.
You see how all of these are coming together at the CCNP level?
Different features, different functions, different things like that.
Right?
So, you'll learn a little bit more about IPSLA later on.
And I'll show you some other options in IPSLA like, oh, my gosh,
why am I drawing a blank?
Oh, floating static routes.
Floating static routes will be covered in that one as well.
I'll also talk about UDP jitter in that one.
So, two important ones for the certification exam.
So, keep an eye out for that when you do that review at that point in time.
And remember what we talked about here when it comes to these things.
All right.
So, a lot of different things, as you can see here,
when it comes to HSRP to get it to work the way you want it to work,
so that way there you can accomplish your particular objectives that you
need to.
All right.
Let's talk about timers now.
So, as we said, with timers, our default timers were 3 and 10.
So, you can easily change your timers to things like 1 is the lowest
and 3 is the lowest if you use that particular command.
So, if you use the command standby, the group number, timers,
the lowest you can do is 1 and then 3 for the actual hold-down timer,
because they recommend 3 times the hello for your hold-down timer.
But there is another command you can use, and that is timers msec,
milliseconds.
So, instead of typing in the time that you want, 1 second and 3 seconds,
type in msec first, and then you can get millisecond,
submillisecond timers, right, subsecond timers.
And so, 500 milliseconds and 2750 milliseconds.
Now, what's the lowest you can actually do?
Standby, 10, timers.
So, just to show you here, you'll see it says 1 to 254 for the hello,
and then they're saying 2 to 255, but they recommend 1 and 3 if that's the
lowest you go.
But if you type in msec, as you can see, lowest is 15 milliseconds.
Okay.
That is probably not going to work for most of you,
because you also have to remember that that is how often a hello packet is
going to be sent.
So, if I do 15 as an example, and then we do our msec, and we say 50,
50 milliseconds,
that means that your devices are going to have to receive a hello packet
once every 50 milliseconds.
And if there's any congestion at all in that layer 2 network where the
hello packet's traversing, if it's delayed by 1 millisecond,
and it goes over 50 milliseconds by 1 millisecond,
you're going to have a failover.
And the last thing you want is for your routers to be failing over,
failing back, failing over, failing back, failing over,
failing back, failing over, failing back.
So, be careful with that in the real world.
Just because you can do it doesn't mean you want to do it.
And even on these devices here, DSW1 and DSW2,
I've done this before as a demo, and I failed over, failed back, failed.
And there's no traffic in this environment.
There's minuscule traffic.
But by the time you transmit it, it gets to the other side.
The other side has to process it.
I mean, it could easily be 50 milliseconds.
So, but those are options you have.
Just keep in mind.
So, fine-tuning them, tweaking them,
so that way there you have minimal packet loss is absolutely a recommended
best practice.
But you now have to think about the fact that you also need to consider your
preemption.
So, we've seen today in all of my examples how preemption occurs pretty
quickly, meaning that if all of a sudden the active routers interfaces come
back up, what happens?
It automatically promotes itself.
So, do you remember the example I gave earlier where PC1,
we were looking at its continuous ping.
We failed over to DSW2, we lost a packet.
We failed back over to DSW1, and we lost a packet.
Okay, I don't want to lose any packets when the active router or the router
becomes active.
So, if we had a failover, and now I'm going back to being active DSW1,
I don't want to lose any packets.
In our case, why did we lose packets?
Well, it could have been because of spanning tree protocol not fully
converging yet.
It could have been because of OSPF not fully converging yet.
Remember, I brought down my interfaces.
So, if I brought down my interfaces and bring them back up, right,
is it possible that if I brought down interface VLAN10,
that OSPF would then have to relearn about that, reshare that?
Yeah, absolutely.
So, the fact is that you don't want to preempt too fast.
So, standby is active right now.
This is nonexistent, meaning when this comes back up, how fast do I take over?
How fast do I become active again?
That's what you want to delay here.
You want to delay that based on what?
Based on everything else that's going on in your environment.
So, you've got to measure that.
You've got to measure that.
So, how do you measure that?
It means you are going to have to figure out how long from the time that these
interfaces come up or these interfaces come up or interface VLAN10 comes up,
how long does it take before the network is stable?
Once you figure that number out, add a few seconds to it,
and that's going to be your delay time.
So, you might want to delay five seconds.
You might want to delay ten seconds.
You might even have to delay a whole minute,
depending on the scenario and situations that you have in your environment.
The last thing you want to do is take over as active,
but the rest of the network is not ready for you.
And if that's the case, then you're just going to drop traffic.
We don't want that to happen.
That's what preemption delay allows you to eliminate.
So, if you do preemption delay minimum, that is for the scenario I just gave you.
Okay, but preemption delay reload is whenever you reload the device.
So, for example, let's say we reloaded this device right now.
Reload, what happens?
I'm no longer active, you're active.
So, when this device finally reloads, its interfaces are going to be up and running,
it's going to start sending hello packets, and all of a sudden it's going to go active.
Well, what if the rest of this has not converged yet for OSPF?
What if there's other features and services that are still turning on?
Then all of a sudden you're active and you're dropping all the traffic
because you don't know where to go with it.
You don't have an updated routing table yet, you don't have this, you don't have that,
this is not working, that's not working.
So, you have to figure out how long does it take my device to fully boot, fully load,
learn everything it needs to learn, converge everything it needs to converge,
and then in the end become stable.
Once you've timed all of that with a stopwatch,
then you know how long you're going to have to delay at a reload to make sure.
Typically what you can do, folks, is just measure the boot time.
How long does it take to boot the iOS?
And then if that took two minutes, add another one minute, so time and a half.
So, add another minute to it.
If it took three minutes, add another minute and a half to it.
And then just wait a little longer.
There's no reason for you to just jump back into the active role
when somebody is already doing okay with it.
That's what these are for.
Keep an eye on those for the certification exam.
All right.
Authentication, something we might want to consider with HSRP.
So, HSRP supports clear text authentication and MD5 authentication.
So, you just do it right under the interface configuration.
So, something like standby 10, and then you go type in authentication,
and then you can do MD5 or plain text authentication.
So, if we went MD5, I would type in MD5.
And then we can either do a key chain or a key string.
So, a key chain is another feature in Cisco iOS where you actually build like a chain,
a chain for keys.
Most of us don't have key chains anymore.
Do you remember a time when you would actually have a key chain?
And on that key chain, you would have like 5, 6, 7, 8, 9, 10 keys on it for everything you did?
Well, that's what we're talking about.
I could create a key chain, and on that key chain, I have many different keys.
And so then I can call the key from that key chain when I'm doing HSRP.
That's all it is.
Or I could just have one key directly created right here.
That's where you type in key string.
So, I type in my key string.
My key string, I'm just going to type in Cisco Rocks.
And then there we go.
So, I'm going to copy and paste that over.
See, you can already see I got a message, bad authentication, because I'm doing authentication
and they're not doing authentication.
So, take a peek.
Right now, you see that?
I'm active.
Okay.
It is putting itself in a standby state.
Let's just double check that.
Nope, it's active.
Look at that.
It's active.
So, both routers are active right now.
Yeah, both routers are active.
See?
So, bad authentication, both routers are active.
Bad group numbers, both routers are active.
Bad IPs, both routers become active.
Things like that can happen.
So, on the exam, if you ever see two routers in the same group are both active, that means
you've got a configuration problem on your hands.
Figure out what it is.
It could be authentication related, group number related.
It could be related to IP address.
Look for things like that.
All right.
So, let me copy and paste that in.
Interface VLAN 10.
Oh, no.
We don't want that.
We should say once I get that sorted out, we should go back to normal.
This should be standby.
The other one should be active.
Actually, do we still have R1's interface down?
Yeah.
So, DSW-2 should – actually, DSW-2 was active to begin with because R1's interface was
down, folks.
We had never brought it back up.
But you can see DSW-1 promoted itself to active because it felt like it was in its own group
and the other one didn't exist.
So, it promoted itself to active.
Even though R1 was down, we still had that.
So, I'm standby now, but I should go to active because my priority is going to be
higher and all that stuff.
So, we'll let that cook for just a bit.
All right.
So, that is authentication.
And lastly, versions, something to keep in mind here.
When it comes to versions, you've got HSRP version 1, which is what I just taught to you.
Version 1 supports groups 0 to 255, so 256 total groups.
But version 2 supports more groups and IPv6.
Right?
So, for the exam, make sure you know that for IPv6, you've got to go to version 2.
So, how do you go to version 2?
It's pretty straightforward.
You're going to type in standby 10 version.
Okay.
So, version is for all groups.
So, no matter what, standby version is going to be for all groups.
So, I'll do version 2 there, version 2 there.
All right.
There you go.
So, no matter what group I have on that device, we're now version 2.
On that interface, I should say.
All right.
What I wanted to point out to you, though, is that notice how we're reinitializing.
You see that?
We're reinitializing.
Why do we have to reinitialize with this?
Well, it's because if we type in do show standby, you're going to see that the MAC address has totally changed.
So, I want you to remember that MAC address now.
00000C9FF.
9FF.
So, if you see 9FF, that is HSRP version 2, and I have it right there on the slide for you.
Why did they have to change it?
Because of this.
See the triple X?
We need three hexadecimal numbers now for the group number.
So, in our case, our group is going to be 00A because it is group 10.
That changes.
So, if you switch from version 1 to version 2, the MAC address changes.
Oh, also the multicast address changes.
So, remember what I said.
Hellos were using 224002.
Well, now they're using 22400102.
Things to keep in mind.
All right.
So, that is HSRP.
That is a lot.
But we've got that covered now.
Question.
If authentication doesn't match and they think they're in their own groups, both would try to use the shared IP.
Yeah, exactly.
And that causes conflicts, right?
So, if you have authentication issues, you have IP issues, you have, you know, whatever issues you have configuration, it really causes problems.
Because, for example, if you had two different IPs as part of the group, then they're both going to make themselves active because they both want to be active for that IP.
Now, even though the end user is given like 10.0.0.254, and that points to whoever is active at the time, that would be DSW1 as an example.
Well, if DSW2 is using 10.0.0.253 as a virtual IP because you goofed it up and you typed in the wrong number, well, then when there's a failover or anything happens, well, then that's the wrong IP.
And so, there is going to be a conflict there, and then things break down on you during any type of failover scenario.
And you would get warning messages to that.
It's not going to work.
It's bad.
A lot of syslog messages will show up to warn you.
But on the exam, they're not going to show you syslog messages ever unless they're testing you on syslog messages.
So, it's important to realize that at any time, if you see two devices that are active, I immediately want you to look at things like, are the IPs accidentally configured differently?
Is the group number accidentally configured differently?
Is authentication accidentally configured differently?
Those are the things to really take a look at.
All right.
HSRP fun.