WEBVTT

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 Hello and welcome to this video which
 is a review or refresher of EIGRP

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 which is also a component that you'll
 see within the new CCNA 200-301

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 exam. So EIGRP is an open standard
 now but it wasn't always that way.

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 EIGRP which stands for the Enhanced
 Interior Gateway Routing Protocol.

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 Cisco a long time ago came up with an
 older protocol that was a competition

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 of RIP. It was called IGRP, the Interior
 Gateway Routing Protocol.

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 There were a lot of things that made
 that Routing Protocol better than

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 RIP. And then they decided
 to enhance it.

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 Hence enhanced Interior Gateway
 Routing Protocol.

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 Now for the longest time for several
 decades EIGRP was Cisco proprietary.

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 But back in 2013 about seven plus years
 ago they decided to document it,

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 put out an RFC for it.

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 And so now we call it
 an open standard.

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 However even to this day you're buying
 large just going to see it running

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 on Cisco devices.

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 It is what we call a hybrid IGP or
 an advanced distance vector IGP.

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 It is an Interior Gateway Protocol so
 just like OSPF is meant to be run

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 within your autonomous system talking
 to other routers within your company.

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 The reason why we call it a hybrid IGP is
 because it does have some characteristics

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 that you would normally find in Link
 State such as building and forming

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 neighbor relationships but also have
 some characteristics you would find

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 in distance vector.

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 Such as you only learn routes from
 your neighbor but you have no idea

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 what the topology looks like
 behind your neighbor.

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 That's a distance vector
 characteristic.

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 The metric the EIGRP comes up with
 and we'll see the formula for this

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 in just a second.

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 We formally call the name
 of the metric distance.

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 So as rip has hop count OSPF
 has cost EIGRP has distance.

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 Now distance is actually the end result
 of a complex formula that computes

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 several different variables
 into the formula.

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 By default that formula factors in
 Link bandwidth and delay to compute

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 distance. But there are a couple of
 other things you can turn on to also

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 factor into the distance
 calculation.

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 EIGRP does support summarization.

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 It does support authentication and it
 supports unequal cost load balancing.

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 What that means is most routing protocols
 if you, for example, let's take

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 rip as an example since
 rip is pretty easy.

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 If I'm a router speaking rip and I learned
 that the 55 network is reachable

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 via this direction at two hops.

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 And it's reachable via this
 direction at seven hops.

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 I'm going to choose the
 path that's two hops.

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 Two hops is less than seven.

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 I'll choose this.

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 Well, if I want to actually load balance
 my traffic across both paths.

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 I have to basically make the hop
 count of two artificially bigger.

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 I have to make this path of the hop count
 to make it look like it's seven.

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 And if I can increase the hop count
 artificially and make it look like

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 it's seven, then they'll both look
 identical and rip will now believe

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 it has equal cost routes and put both
 of those routes to the 55 network

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 into the routing table.

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 It load balance my packets
 across them.

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 So all routing protocols give you that
 ability to take unequal cost routes

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 and tweak them to the point where they
 are equal or they seem equal to

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 the routing table.

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 So I have one route
 to the 55 network.

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 This is the best.

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 I have another route to the 55
 network, but it's not as good.

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 Normally, EI JRP would say this is the
 one I'm going to put in my routing

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 table. I'm not going
 to put any other one.

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 But with EI JRP with a single command,
 you can put them both in the routing

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 table as they are clearly unequal.


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 And then now we can do unequal
 cost load balancing.

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 We can send more packets
 across this direction.

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 But we can still send some packets
 across this direction right here.

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 EI JRP has the reserved IP
 address of 224.0.0.10.

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 And most packets go to that.

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 EI JRP like like OSPF does utilize Hello
 packets to build neighbor relationships.

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 After a Hello packet exchange takes
 place, then we will exchange EI JRP

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 update packets, which is where we tell
 each other about the routes we

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 have. EI JRP updates do have sequence
 numbers in them, so they do have

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 to be acknowledged.

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 EI JRP also has query
 and reply packets.

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 If I was normally going this way to
 reach the 95.95 network, and all of

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 a sudden that path failed, or I lost
 that route, I can actually turn to

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 you, my other EI JRP neighbor, and send
 you an EI JRP query packet saying,

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 hey, do you have a route
 to the 95.95 network?

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 And then you would respond to me with
 an EI JRP reply, either saying,

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 yes, you do or no, you don't.

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 So here is the EI JRP metric.

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 Now, don't worry, no Cisco exam that
 I know of requires you to memorize

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 this formula. But there are some
 key takeaways from this.

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 So remember, the total result of this
 is going to be some big number,

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 and we're going to call
 that number distance.

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 But distance is composed, as you can see
 here, of several different variables.

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 It takes the bandwidth of an interface
 and actually plugs that in twice

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 in here. It takes the delay, takes reliability,
 and it factors in load.

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 Now, by default, it does not factor
 in all of these variables, because

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 notice that each one of these things is
 either added to, multiplied against,

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 or divided by something
 called a K value.

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 Well, if we look at the default values
 for the K values, and once again,

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 no worries, you don't
 have to memorize this.

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 Take a look at this.

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 We can see here that K2 is zero, which
 means here we have zero times the

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 bandwidth, which means
 this is basically zero.

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 So load is not a factor.

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 As long as K2 is a zero, we can't
 use the interface load.

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 Also, K4 and K5 are zero, which are applied
 over here against reliability.

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 So it says this part of
 the formula is not used.

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 So what we end up having, if those
 parts of the formula are not used,

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 as I mentioned, EHRP utilizes Hello packets
 to form neighbor relationships.

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 Those packets are transmitted to the
 multicast address of 224.0010.

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 And you can see here, there are
 three things that have to match.

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 Number one, the source IP subnet.

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 In other words, if you and I share
 a cable, we're connected.

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 But when I send a Hello, I say,
 Hello, my IP address is 1.1.1.1.

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 And when you get it, your interface
 directly connected to me has 4.4.4

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.4 on it. Well, that means even though
 we're on the same cable, we're not

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 in the same subnet.

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 So we will not form EHRP
 neighbor relationships.

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 The K values, we just saw those K values
 of like 1, 0, 1, 0, those have

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 to match. So if somebody changes the
 K values on one router, they're going

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 to lose all their EHRP neighbor relationships
 unless they go to the surrounding

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 routers and make those
 K values match.

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 It is not recommended to
 modify the K values.

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 And the autonomous system
 value has to match.

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 Here's something that's a little bit
 different between OSPF and EHRP.

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 Both OSPF and EHRP are interior
 gateway protocols.

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 They are designed to run within
 an autonomous system.

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 Now with OSPF, if you receive an OSPF
 Hello packet from me, there's no

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 mention in there of what
 the autonomous system is.

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 OSPF has no idea what the autonomous
 system number is.

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 There doesn't even
 care about that.

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 So if you receive an OSPF packet from
 me, you're just going to assume

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 that I am in the same autonomous
 system as you.

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 That I'm part of the
 same company as you.

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 EHRP makes no such assumptions.

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 When you configure EHRP, you know, there's
 actually a couple of different

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 ways to configure it.

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 But for example, here on this
 router, I've configured EHRP.

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 It was called EHRP classic
 mode right here.

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 And notice I have router EHRP 100.


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 Now, an OSPF, if I did router OSPF
 1, that number after the word OSPF

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 was just a locally significant
 process ID.

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 It didn't mean anything.

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 It was not exchanged with
 any neighbors or anything.

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 Could be anything you wanted.

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 Here in EHRP, that is
 not a process ID.

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 That is an autonomous
 system number.

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 I've actually told EHRP the number
 of your company, of your autonomous

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 system, is 100. And that number
 is exchanged in EHRP.

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 Hello packets. So you and I have to
 be in the same autonomous system or

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 we will ignore each other.

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 Now, one difference between another
 difference between OSPF and EHRP are

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 the timers. In the world of OSPF, my
 hello timer and my dead interval

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 had to match yours.

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 By default, it was probably going to be
 10 seconds for the hello, 40 seconds

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 for the dead interval,
 which matched yours.

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 Now, in OSPF, if those timers did not
 match, if I went onto my interface

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 connecting to you and on my interface,
 I changed those timers in some

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 way, that was okay.

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 It would not affect our
 neighbor relationship.

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 Actually, I'm sorry, in OSPF, it does
 affect the neighbor relationship.

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 In OSPF, the timers have to match.


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 But here in EHRP, they do not.

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 The timers do not need to match.

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 It will not change the neighbor relationship
 if they don't match.

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 And the effective passive interface
 in EHRP is exactly the same as in

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 OSPF. Just like in OSPF, how would you
 say passive interface fast ethernet

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 00? That means that interface is not
 allowed to send out hello packets.

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 And clearly, if I'm not sending out hello
 packets on an interface, I can't

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 form a neighbor relationship
 on that interface.

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 Or if I did have an existing neighbor
 relationship and then I made that

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 interface passive, it would kill that
 neighbor relationship because I

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 would stop sending hello's.

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 The exact same thing is true with EHRP,
 if you use passive interface with

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 EHRP. Another thing to be aware of
 is that EHRP categorizes routes as

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 either EHRP internal
 or EHRP external.

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 Now you can see here, there's a couple
 of different ways you can advertise

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 routes in EHRP. The most common way
 is the network command, very similar

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 to OSPF. Just like in OSPF, if I had
 a directly connected interface, a

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 network, I said network, whatever,
 and then I had a wildcard mask and

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 an area number. And that allowed me
 to advertise this network inside of

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 an LSA. Well, here in EHRP,
 it's very similar.

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 There's no wildcard
 mask or anything.

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 There's no area.

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 But this is telling EHRP, hey, if you
 have any directly connected networks

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 that start with 21, you
 can advertise that.

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 And those will go out as
 EHRP internal routes.

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 As a matter of fact, the way we see
 those is if you look in your routing

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 table, any route that is preceded by a
 capital D is an EHRP internal route.

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 Now, the other way that you can advertise
 routes in EHRP, and this is

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 typically one of when you want to take
 routes that are not EHRP, like

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 OSPF routes or RIP routes
 or static routes.

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 And you want to convert them
 into EHRP and send them.

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 To do that, you use the
 redistribution command.

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 Now, you're not really expected to
 know how to use the redistribution

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 command at the CCI level.

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 But I do want to show you this.

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 So in this particular router, he's
 sending out hellos on his directly

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 connected network of 22.

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 And any other networks he has, like loopbacks
 or something, he's redistributing

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 those into EHRP.

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 Well, when you use the redistribute
 command to send something into EHRP,

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 that creates an EHRP
 external route.

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 And you can see that shows
 up here as a DEX.

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 So why do we care?

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 Well, once again, when it comes down
 to if a router receives like this,

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 if here comes down, I should probably
 use a different color than that.

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 If this router right here receives
 two EHRP updates, let's say router

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 one is sending one and router two
 is sending one to router X.

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 And they're both connected
 to the exact same network.

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 Let's say the five
 dot five network.

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 Now router one, he used the network
 command network five.

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 That means he's going to send
 down an EHRP internal route.

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 For that network.

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 Router two, he decided
 to do redistribute.

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 Which means he's sending
 an EHRP external route.

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 So now router X is just received two EHRP
 updates for the exact same prefix.

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 How is he going to choose
 which one is the best?

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 Well, he's going to always choose
 the one with the lowest distance.

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 No, if they were both the same, if they
 were both internal or they were

0:14:06.300000 --> 0:14:10.620000
 both external, then yes, he would use
 the EHRP distance in which everyone

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 had the lowest distance.

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 That's one he'd select.

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 But these are not the same.

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 These are two different
 kinds of EHRP routes.

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 And as we can see here in the slide,
 it's all based on administrative

0:14:20.960000 --> 0:14:26.760000
 distance. EHRP internal routes are always
 preferred because their administrative

0:14:26.760000 --> 0:14:32.220000
 distance is 90 as compared to EHRP external
 routes where the administrative

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 distances much higher 170.

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 So it doesn't make any difference with
 the distances as far as you know,

0:14:40.240000 --> 0:14:48.020000
 five dot five here could have an
 EHRP distance of 10 million.

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 Five dot five dot here could
 have a distance of 500.

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 This one would always be preferred because
 it has a lower administrative

0:14:56.880000 --> 0:15:06.840000
 distance. All right, some additional terminology
 you need to know, successor

0:15:06.840000 --> 0:15:09.220000
 and feasible successor.

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 Let's go back to that
 example I just gave.

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 I've just learned about
 the five five network.

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 I've picked my internal route.

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 That's the best one.

0:15:16.440000 --> 0:15:19.900000
 And I've got my external
 route as a backup.

0:15:19.900000 --> 0:15:24.340000
 Well, in this case, the neighbor, the
 EHRP neighbor that sent me the EHRP

0:15:24.340000 --> 0:15:26.500000
 internal route that sent
 me the best route.

0:15:26.500000 --> 0:15:28.620000
 We call him my successor.

0:15:28.620000 --> 0:15:31.460000
 So to get to the five five network,
 he is my successor.

0:15:31.460000 --> 0:15:32.720000
 He's the best path.

0:15:32.720000 --> 0:15:35.920000
 This other guy here I'm keeping waiting
 the wings that the net, the neighbor

0:15:35.920000 --> 0:15:37.280000
 who sent me that route.

0:15:37.280000 --> 0:15:43.220000
 He's a backup. But what we technically
 say is he is my feasible successor.

0:15:43.220000 --> 0:15:51.840000
 All right, and the difference between feasible
 distance reported and advertised

0:15:51.840000 --> 0:15:56.460000
 distance. Okay, so let's start
 with the bottom one first.

0:15:56.460000 --> 0:16:00.720000
 So let's say we have
 something like this.

0:16:00.720000 --> 0:16:04.020000
 Here's router one.

0:16:04.020000 --> 0:16:06.100000
 He has learned of some network.

0:16:06.100000 --> 0:16:08.380000
 Let's just say it's
 a five five network.

0:16:08.380000 --> 0:16:13.280000
 And he advertises
 it to router two.

0:16:13.280000 --> 0:16:17.980000
 When router one advertises it to router
 two and he says, Hey, let me tell

0:16:17.980000 --> 0:16:19.740000
 you about the five five network.

0:16:19.740000 --> 0:16:22.140000
 He's going to include
 some information.

0:16:22.140000 --> 0:16:25.680000
 Like, Hey, from my perspective
 from router one's perspective.

0:16:25.680000 --> 0:16:29.460000
 This is the bandwidth that I believe
 it is to get to that network.

0:16:29.460000 --> 0:16:31.420000
 This is the delay.

0:16:31.420000 --> 0:16:34.140000
 I believe it is to get
 to that network.

0:16:34.140000 --> 0:16:35.660000
 The reliability.

0:16:35.660000 --> 0:16:41.140000
 The load. So he gives all those things
 technically these things here.

0:16:41.140000 --> 0:16:44.100000
 Are called vector.

0:16:44.100000 --> 0:16:52.440000
 Metrics. So he gives those vector
 metrics to router two.

0:16:52.440000 --> 0:16:57.160000
 Now router two puts that stuff into
 the formula and comes up with.

0:16:57.160000 --> 0:16:59.820000
 Let's say 50,000.

0:16:59.820000 --> 0:17:10.740000
 So he says, this is our ones distance
 from router one's perspective.

0:17:10.740000 --> 0:17:14.580000
 His reported distance is 50,000.

0:17:14.580000 --> 0:17:15.620000
 That's what our two saying.

0:17:15.620000 --> 0:17:19.040000
 He says, okay, if I was actually router
 one right now, if I was sitting

0:17:19.040000 --> 0:17:22.280000
 on router one, the distance
 would be 50,000.

0:17:22.280000 --> 0:17:24.780000
 That is reported or
 advertised distance.

0:17:24.780000 --> 0:17:28.440000
 What has been advertised to
 you from your neighbor.

0:17:28.440000 --> 0:17:33.040000
 Then router two says, but for me, I
 have to factor this link into the

0:17:33.040000 --> 0:17:38.720000
 equation. So router two takes the
 information that he learned.

0:17:38.720000 --> 0:17:43.720000
 Also factors into that his own bandwidth
 delay, reliability and load and

0:17:43.720000 --> 0:17:45.040000
 comes up with his.

0:17:45.040000 --> 0:17:46.080000
 Computer distance.

0:17:46.080000 --> 0:17:47.140000
 That's going to be
 a little bit more.

0:17:47.140000 --> 0:17:51.380000
 Let's say that's 50,800.

0:17:51.380000 --> 0:17:53.680000
 That's his computed distance.

0:17:53.680000 --> 0:18:00.700000
 Now, if this is the only path.

0:18:00.700000 --> 0:18:04.380000
 The router two has to get to the five
 five network that computed distance

0:18:04.380000 --> 0:18:06.480000
 end up being his best distance.

0:18:06.480000 --> 0:18:09.140000
 It's the only distance he has,
 but it's the best distance.

0:18:09.140000 --> 0:18:18.100000
 And the best distance is called
 the feasible distance.

0:18:18.100000 --> 0:18:21.280000
 Is he if router two had learned about
 that five five network from somebody

0:18:21.280000 --> 0:18:25.060000
 else. So let's do it.

0:18:25.060000 --> 0:18:37.060000
 Let's do this. Let's say that router
 two had this in this table.

0:18:37.060000 --> 0:18:43.020000
 He said, okay. I just come, let's say
 there's over here a router three

0:18:43.020000 --> 0:18:46.120000
 who also advertised the
 five five network.

0:18:46.120000 --> 0:18:50.800000
 He says, okay, five five network.

0:18:50.800000 --> 0:18:58.680000
 He says the, I've learned
 about it via router one.

0:18:58.680000 --> 0:19:02.200000
 And for router one.

0:19:02.200000 --> 0:19:07.320000
 His advertised distance
 was 50,000.

0:19:07.320000 --> 0:19:14.540000
 When I factored in my distance to
 get to him, I came up with 50,800.

0:19:14.540000 --> 0:19:20.620000
 All right. Then I also learned
 about it via router three.

0:19:20.620000 --> 0:19:23.700000
 So remember what these
 terms are here.

0:19:23.700000 --> 0:19:28.360000
 This here is the reported
 or advertised distance.

0:19:28.360000 --> 0:19:33.760000
 This here is the computed
 distance.

0:19:33.760000 --> 0:19:37.820000
 I learned about that same
 route from router three.

0:19:37.820000 --> 0:19:44.120000
 His advertised distance, his
 reported distance was 65,000.

0:19:44.120000 --> 0:19:48.440000
 And when I factor in what takes me to
 reach that neighbor, I came up with

0:19:48.440000 --> 0:19:52.900000
 68,000. All right.

0:19:52.900000 --> 0:19:58.220000
 So once again, this is the computed distance
 to go through that neighbor.

0:19:58.220000 --> 0:20:02.260000
 That is the neighbor's reported
 or advertised distance.

0:20:02.260000 --> 0:20:05.960000
 Now router one says, I've got two
 paths to get to that network.

0:20:05.960000 --> 0:20:09.420000
 When I take a look at my two
 computed distance values.

0:20:09.420000 --> 0:20:13.320000
 This one is the best because
 that's lowest.

0:20:13.320000 --> 0:20:19.580000
 So that will be my feasible
 distance 50,800.

0:20:19.580000 --> 0:20:26.060000
 And the way you can practically
 see that in a router.

0:20:26.060000 --> 0:20:28.520000
 Is by using the command.

0:20:28.520000 --> 0:20:33.860000
 Show IP EI JRP topology.

0:20:33.860000 --> 0:20:38.120000
 If you use your topology table
 where this stuff is stored.

0:20:38.120000 --> 0:20:42.360000
 So you can see he says, Hey,
 I learned the 123 network.

0:20:42.360000 --> 0:20:44.640000
 I learned it from this neighbor.

0:20:44.640000 --> 0:20:48.400000
 His reported distance is 2,816.

0:20:48.400000 --> 0:20:51.700000
 And when I factor in what
 takes me to get to him.

0:20:51.700000 --> 0:20:55.300000
 My computer distance is 3,072.

0:20:55.300000 --> 0:21:00.420000
 As it so happens, he's the only person
 who ever reported that to me.

0:21:00.420000 --> 0:21:04.740000
 So that is also my best distance,
 my feasible distance.

0:21:04.740000 --> 0:21:13.680000
 And the last thing I want to cover here
 is that EI JRP maintains its own

0:21:13.680000 --> 0:21:20.020000
 neighbor table. You can view that with
 the command show IP EI JRP neighbor.

0:21:20.020000 --> 0:21:24.200000
 You can see the neighbors that you have
 and the interfaces that you learned

0:21:24.200000 --> 0:21:29.420000
 them on. EI JRP also has
 the topology table.

0:21:29.420000 --> 0:21:30.720000
 We just looked at that.

0:21:30.720000 --> 0:21:35.820000
 That's where EI JRP stores every
 route it has ever learned.

0:21:35.820000 --> 0:21:40.520000
 And every route it has ever
 advertised to anybody else.

0:21:40.520000 --> 0:21:46.340000
 And of course, EI JRP can take the best
 routes and put them into the routing

0:21:46.340000 --> 0:21:53.140000
 table. And you can view that by either
 typing show IP route and looking

0:21:53.140000 --> 0:21:56.420000
 for any route that begins
 with a D is in David.

0:21:56.420000 --> 0:22:04.560000
 Or you can just say show IP route EI
 JRP and just view your EI JRP routes.

0:22:04.560000 --> 0:22:11.460000
 So that concludes this
 refresher on EI JRP.

0:22:11.460000 --> 0:22:12.580000
 I hope you found it helpful.