WEBVTT

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 Hello and welcome to this refresher on
 HSRP, which is a first hop redundancy

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 protocol that you need to know
 for the CCA 200-301 exam.

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 So the whole idea behind first hop
 redundancy protocols, whether it be

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 HSRP, VRRP or GLBP, is that we want to
 provide two or more routers connected

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 to the same land and we want one to
 be a redundant backup for the other.

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 And ideally, we want our clients, our laptops,
 PCs and servers to be completely

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 unaware that we've done that.

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 We want this whole thing to
 be transparent to them.

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 So HSRP is one protocol
 that does that.

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 It is Cisco proprietary, stands for
 the hot standby router protocol.

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 And the way HSRP accomplishes
 this is pretty elegant.

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 So basically what you do is you configure
 HSRP on the two interfaces that

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 lead to your LAN to your subnet.

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 Both interfaces will have their own IP
 addresses just like you would normally

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 see. But what's different is when you
 configure HSRP on those interfaces,

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 those interfaces also both
 have a virtual IP.

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 We've seen that right here, which is
 1.1.1.1 virtual IP of 1.1.1.1.1.

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 They will also create
 a virtual MAC address.

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 So in addition to having their real
 MAC addresses on their NIC cards,

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 not only will those two interfaces share
 the same virtual IP, they will

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 share the same virtual MAC.

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 Just to make it simple, I'll
 just put AA in here.

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 Now once that's done, one of these
 routers will be elected to the HSRP

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 active status. So now, if anybody here
 wants to learn of their gateway

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 via DHCP, that their
 gateway is 1.1.1.1.1.

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 The next thing they're launching to
 do is ARP for their default gateway.

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 And when they ARP for 1.1.1.1, the
 HSRP active router will respond to

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 that ARP saying, hey, I'm 1.1
.1.1 and my MAC address is AA.

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 And now that he is active, any actual
 packets, or I should say, Ethernet

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 frames, that this router sends going
 to a destination MAC address of AA

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 will be picked up by the active router
 and the active router will forward

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 those packets. Now, clearly, the standby
 router needs to have some way

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 of monitoring the active router.

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 So if the active router goes down,
 the standby router is aware of that

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 and the standby router
 can take over.

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 And that's what we're
 looking at right here.

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 So both the active router and the standby
 router send out periodic hello

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 packets by default it's every
 three seconds for HSRP.

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 And those hello packets use UDP port
 1985 and they go to the destination

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 address of 224.002.

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 So that is not for the purposes
 of the laptops, PCs and clients.

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 They don't pay attention to that.

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 That's just so both routers
 are aware of each other.

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 And so the standby router can know
 if the active router disappears, if

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 the active router's hellos vanish.


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 If that's the case, then the standby
 router would just simply change his

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 state and the standby router
 would become active.

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 Now who has elected
 the active router?

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 Well, if both of these routers are
 configured for HSRP pretty much at

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 the exact same time, then it'll be the
 router with the highest HSRP interface

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 priority. As you can see
 here, the default is 100.

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 So if I want to make the top router
 active, I could just configure his

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 interface priority to be something
 higher than 100.

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 Now with HSRP, if I configured HSRP
 on the top router, let's say, hey,

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 and I hit enter.

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 Okay, so that top router is going to
 start sending out HSRP hello packets.

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 He's going to listen to see if anybody
 wants to elect with him, if anybody

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 wants to fight with him to see
 who's going to be active.

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 He's not going to wait forever.

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 So with HSRP as with several other
 protocols, in this case, he's only

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 going to wait a short
 period of time.

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 It's only about 10 or
 15 seconds or so.

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 So if I don't configure the bottom router
 for HSRP within that time period,

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 the top router will become active.


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 They'll say, hey, there's
 nobody out here but me.

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 I guess I'm active.

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 And then once the HSRP active router
 is elected, even if somebody comes

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 onto the land later on with a better
 priority, it's too late.

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 The active router
 is already there.

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 Now, what if they both come online
 at exactly the same time and their

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 priorities are the same,
 then who's elected?

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 Then it's whoever has the
 highest IP address.

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 So in this case, the top router would
 still win because he's got a higher

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 IP address than the bottom router.


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 1113 beats 1112.

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 So the virtual IP address is
 something you configure.

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 Now for the CCNA, it does not expect
 you to know how to configure HSRP,

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 but if you want to practice this
 in the lab, it's very simple.

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 You just go to this interface, make
 sure it already has an IP address

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 and it's up. And on the interface, you
 just do the command stand by, put

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 in a number that's your
 standby group number.

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 Most people typically start with standby
 group number one, and then you

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 say IP, and you put in whatever your
 virtual IP address is, 1.1.1.1.

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 Then replicate that exact same
 command on this interface.

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 And now those two routers will
 be participating in HSRP.

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 Now, like I said, you have to configure
 the virtual IP address.

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 Those two routers will also derive a
 shared virtual MAC address as well,

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 because our clients out there need to
 know what the virtual MAC address

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 is that's associated to
 that virtual IP address.

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 You don't have to configure that.

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 HSRP will dynamically derive
 that virtual MAC address.

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 And you can see here, that's
 the format of it.

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 So we'll take that format where the
 last two characters will be whatever

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 your HSRP group is.

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 So if I did stand by 12, well, stand
 by 12 would be zero C, right?

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 Because C in hexadecimal is 12.

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 That would end up becoming
 my virtual MAC address.

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 As I mentioned, preemption
 is off by default.

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 Preemption, if preemption was on, if
 it was enabled, that would mean any

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 router could come along at any point
 in time and take over the role of

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 active status if that router had
 a higher priority or IP address.

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 But that's not on by default.

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 You can turn that on though.

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 And there's no load
 sharing with HSRP.

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 What that means is if I have these two
 routers, all the packs are going

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 to be routed through one router.

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 So even though the standby router over
 here has a good link to the backbone,

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 he has a good link to the corporate
 network, his backbone connection is

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 not being used because
 he's standby.

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 He's not routing packets.

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 But you can use multi-group
 HSRP to do load sharing.

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 That's above and beyond though,
 the scope of the exam.

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 So how we turned on, I
 just showed you that.

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 Standby, your group number, IP
 and your virtual IP address.

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 Here's how you would change the priority
 of the interface to influence

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 the active router election.

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 And if you want to turn on preemption,
 you can do that.

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 Standby 1 preempt.

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 Now, if I do that on a router, that
 router now has the ability to take

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 over the role of active status
 from an existing active router.

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 And the commands for verification of
 HSRP are simply show standby and

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 show standby brief.

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 So that concludes this
 overview of HSRP.