EIGRP Fundamentals | Cisco CCNA 200-301

being surprised by something like you know a surprise party or a surprise get-together or a surprise gift it's wonderful and other times surprises are not so good for example if we're in the middle of a certification exam and we see some content or some topics that are not listed on the blueprint the exam topics that's not the best way to be surprised so in this video i'd like to help you solve that problem regarding a routing protocol in the world of cisco and to emphasize this point let's talk about a problem that every router has on the network and that is oh no what do i do i just gotta pack it how in the heck do i forward this packet in the right direction so this packet can get like from bob the user over to the server that bob's trying to reach so let's imagine that bob is over here and the server that bob is trying to reach is over here and this server is on the 10.4.0 network with a 24-bit mask and perhaps its ip address is like that 10 or something like that so if bob being the client that he is is going to use his default gateway which would be this interface here on r1 r1 when he gets a packet destined for 10.4.0.10 that router needs to know okay what do i do with this how do i forward it now one solution to this is to use a routing protocol so if we consider these networks like streets so those are street names and we consider a routing protocol that would mean that each of these routers that are connected to streets would be willing to talk to their adjacent router so r4 could tell information about this network this street 10.4 it could tell it to r3 and then r3 could tell that information r2 and r2 could tell that information to r1 and that's the basic idea of a routing protocol allowing these routers to communicate amongst themselves to educate the routers on hey if i do get a packet for this street or that network how do i forward it and by using a dynamic routing protocol these routers can automatically share that information with each other now although there are lots of different routing protocols the routing protocol i'd like to chat with you about in this video is called e i g rp the enhanced interior gateway routing protocol so give me an e give me an i give me g give me an argument so eigrp has been around for a long time and it is not i repeat it is not listed on the blueprint for the ccda but am i hearing a lot of people saying boy i wish i'd known a little bit more about eigrp before i went in for the certification the answer to that question is yes so with that in mind let's take a closer peek at how eigrp this routing protocol that shares information between routers about how to reach networks let's take a closer look at how it works so to do that let's focus on this street name which in ipnetworking we call it a network address this 10.4.0 network which represents this group of devices over here or the street of network devices and if we're running a dynamic routing protocol we have some options we could use rip which is a dynamic routing protocol letting them talk to each other we could use eigrp we could use ospf and they each behave a little bit differently but we're going to focus on eigrp so let's imagine that we have enabled so it's like an app on a phone you turn on the app and you enable it boom it starts working well and imagine we enabled eigrp this routing protocol on each of these routers and they start talking to each other so the question is what are they saying to each other so with the igrp there's a lot of information that r4 regarding this network that is going to share with r3 but i want to share with you the most important aspects of what information is going to share regarding the street with r3 and it boils down to this r4 is going to tell r3 hey dear mr r3 there's this network 10.4.0.0 with a 24-bit mask come join me for subnet saturdays if you don't understand ip addressing yet and we'll get you all sorted out now as r4 communicates over to r3 and says hey i know about this network this street 10.4.0 it's also going to share with r3 something called the delay now a delay is associated with an interface by default so if this interface is a gigabit interface the delay is 10 microseconds now a microsecond is one one millionth of a second so r4 says hey i know about this network 10.4.0 and the delay is 10 microseconds he's directly connected to it on this interface right here so he says here's the network here's the delay of 10 microseconds the other thing that's critical that r4 is going to communicate over to r3 as we talk about this street this network besides the delay is the bandwidth on that interface so if this interface is a gigabit interface that information regarding the bandwidth would be communicated as part of the eigrp routing information for that network so a gigabit is 1 million kilobits per second so let's do a quick recap r4 is advertising the 10.4 network over to r3 and it's including two basic pieces of information actually a lot more than that but two that are important and those two elements are the delay and also the bandwidth associated with that network now you might say well keith uh bandwidth and delay how do we verify that that's a great question let's take a closer look at how r4 knows about the bandwidth and delay for that network of 10.4 that it's advertising so if we go to packet tracer and you might be saying oh no keith are we gonna have a package pacer lab associated with this the answer is yes we are so i'll make this available there's gonna be a link below where you can just click on the link download this packet fisher lab i'm using version 7.31 for this version of the packet tracer lab so you can do this hands-on right alongside with me if you would like so here on r4 if we go to r4 and we do a show ip interface brief i just want to verify we have the correct interfaces involved so this interface right here gigabit ethernet 0 1 is directly connected to the 10.4.0 network and if we do this command show interface gig zero slash one and press enter oh no no too much data well there is a lot of output here from this command which is show interface gig zero slash one but the critical pieces we need it right here and this is specifying that the bandwidth associated with that interface where that network lives is one and i'll just highlight three zeros here is one million kilobits per second meaning it's one gigabit and the delay associated with that interface says this router is 10 microseconds and a microsecond is one one millionth of a second so that's ten of them right here associated with that network so what should happen as r4 is advertising the 10.4 network over to r3 it should be including the bandwidth associated with that network and also the delay so we should expect to see a 1 million kilobits per second regarding bandwidth and a delay of 10 microseconds and i thought to myself oh man it would be so darn cool to do a packet capture like with wireshark or something like that and actually show that advertisement from r4 to r3 that includes those two important factors of the delay and also the bandwidth i thought to myself you know what let's do it and here it is this is an update being sent from r4 over to r3 and if we take a look at the payload so at layer 3 here's the layer 3 header it's pointing to the layer 4 protocol of 88 which is a layer 4 protocol or eigrp and then if we expand eigrp and take a look at it here we have that route that 10.4.0 network that's being advertised if we expand it we can take a closer look at what's in the details regarding that network that r4 is advertising to r3 so if we scroll down a little bit and expand the wide metrics section here there's a lot of details here but here are the points that are really important and that is the bandwidth so that bandwidth is one million in kilobits per second which is one gigabit and here's the delay which is 10 million representing 10 microseconds so good news we're advertising that literally from r4 to r3 regarding that 10.4 route now how do we verify or what do we do with that information on r3 once we learn about it now in eigrp the two major factors that routers are going to use as they calculate the metric now in ospf would be cost for rip it'd be the hop counts in eigrp we call it a composite metric and the way that this metric is calculated regarding any given route it's going to take the worst bandwidth in the path and a sum of the delays so if r4 just advertised that the bandwidth is one gigabit and this is also one gigabit r3 says great i'll just keep using the value of one gigabit in my calculations but but because my own interface says r3 has a delay of 10 microseconds i'm going to go ahead and take the advertised delay of 10 microseconds that you sent add that to my 10 microseconds for my own interface and the result would be 20 microseconds so the secret here is for the composite metric it's a combination of the worst bandwidth in the path and the sum of the delays so worst bandwidth in the past some of the delays so if r4 advertised a delay of 10 microseconds and our own interface is 10 microseconds we'll verify here in a moment r3 is going to consider the delay the sum of the delays up to this point to be 20 microseconds the 10 that r4 offered or advertised and the r3s zero slash one interface that has its own 10 microsecond delay so we can verify that here in packet tracer and we can go to r3 and here on r3 we just do a show iprout so here's the route for 10.4.0 it was learned via eigrp that's the d there on the left hand side and if we do a show iprout we plug in that network and i'll just copy and paste it here copy that right click copy and paste and press enter it'll give us the details regarding just that route check it out it's saying the total delay is now 20 microseconds well why is that well it's because r4 said the delay is 10 microseconds from my perspective and r3 said well my interface has a 10 microsecond delay as well on my gig zero slash one so i'm going to add that to it as part of the calculation and we could verify that with a show interface gig zero slash one and let me show you where that is in the topology that's this interface right here that r3 is learning the route on and that's what we're going to look at right now so here's a show interface gig zero slash one and i'm gonna just do a pipe symbol and say include any lines that have a capital bw in it and that will show us just that one line of output that we're focusing on so here showing that the bandwidth is still 1 million kilobits per second because everybody to this point is using gigabit ethernet but check this out my interface delay on gig 0 1 is 10 and that's why we got an advertised of 10 microseconds and we have our own 10 and that's why for our eigrp composite metric we're using now the factors of the minimum bandwidth in the path which is one gigabit per second and now on router 3 the microsecond total of 20 microseconds so let's discuss a few things on this interface right here which is directly connected to the 104 network the it's a gigabit and the default delay is 10 microseconds on this interface where we're learning the route it's also a gigabit interface and by default it has a delay of 10 microseconds and the same thing is going to be true for here and here so if each interface as that route gets propagated so r4 tells r3 r3 advertises it over here with a sum of the delays of 20 and r2 is going to add 10 more it should be 30 here and if r2 advertises a delay of 30 over r1 r1 should see a delay of 40. so to verify that and you can do this in the packet tracer lab as well let's go to r1 we'll take a look at the details for 10.4.0 and let's just verify that he believes that the sum of all the delays up to him right here at r1 the sum is 40. that would be 10 here 10 more here 10 more here for a total of 40 with r1's delay being added so here in r1 let's do a show interface gig zero slash one just to verify that his delay by default is 10 microseconds there it is right there and then let's do a show iprout so he's got the route to 10.4.0 it was learned via ea grp there's the composite metric right there and to create that composite metric r1 took the advertised information including the the delays up to that point that r2 had and also the worst bandwidth in the path and then calculated this composite metric on his own router so here on r1 if we do a show iprout and we just put in that specific route by copying it and pasting it in it'll give us additional details regarding that specific route and check it out look at this 40 microseconds so there is the metric that it calculated we also call that the feasible distance in the world of eigrp and there is the minimum bandwidth in the path of one million kilobits per second which is one gigabit and it used this sum of the delays and the minimum bandwidth in the path to calculate that final composite metric now you might be thinking you know what i'd like to get my hands on that packet tracer lab and give this a go and verify all that great i encourage you to do it i'll put the link in the description just download it and have at it again it's package tracer version 7.31 that i'm using for this demonstration now um how would we tweak it or modify it in reality we could modify either the bandwidth on any of those interfaces any of those gigs 0 1 interfaces or the delay on any of those gig 01 interfaces and that would modify the downstream router's opinion and metric calculation for those routes so let's go ahead and devise a plan on what to tweak and modify i'll demo it and then my friends i want you to do it in the packet tracer lab so let's do this as a tweak if we took r3's gig zero slash one interface which has a uh default delay of 10 microseconds and we made it 110 instead of 10 that means the metric over here on r1 should go from 40 to 140 if we're going to increase it by a hundred that's also going to affect on r1 the ending final metric that it uses because it's using the sum of the delays it's also using the lowest bandwidth in the path so on our three gig zero slash one let's modify artificially the delay to make it look like 110 microseconds instead of its default of 10. so here in packet tracer let's hop over to r3 and we're going to modify this interface gig 0-1 and increase its delay so here on r3 we'll go into interface configuration mode for gig 0-1 and we will specify a delay of now it wants this delay in tens of microseconds so if we said 11 times 10 that would be 110 microseconds let's go ahead and specify that it automatically balance the neighborship for us which may or may not happen on live gear but that's okay and then we'll do a do show interface gigabit ethernet 0 1 and i'm going to say pipe include bw so we can go ahead and take a look look at that right there so i just wanted to verify that the delay truly had been changed to 110 so because we just bumped up on r3 on this gig zero slash one interface the delay from 10 to 110 the result over here on r1 of the sum of the delays should be now 140 instead of 40. because we increased it 100 over here on our three it should increase by 100 over here as part of the sum total of all the delays over here on r1 let's verify that so we'll make a road trip over here to r1 and on r1 where it was 40 microseconds just a few moments ago and we'll just use the same command show iprout and boom check it out it is now 140 microseconds also notice that the metric increased from it was 35.84 and now at 61.44 because it's taking into consideration the sum of the delays across the network as part of the composite metric the other thing we can do while we're here we got the lab open let's do it is right now it's looking at the worst bandwidth in the path and currently everybody's gigabit ethernet so that's the worst bandwidth however we could tweak that too so the way the worst bandwidth works is if there's ever bad news like if r3 says oh no i've got a 64k connection really really slow it's going to advertise that as the worst possible bandwidth in the path between itself and the destination network and r2 would say oh no 64k i'll pass that along it's like you know gossiping rumors passing on the worst possible information as far as you know the situation so once we have a lower bandwidth all the other routers that are advertising that are going to propagate that lower information so let's do that let's go here on r3 and we'll modify gig zero slash one that instead of using the default bandwidth which is one gigabit per second or a million kilobits per second that we wanted to use something really really bad like 64k so back in packet tracer we'll go back to r3 and we're going to tweak this interface right here gig zero slash one and specify that we wanna tell it that the bandwidth on that interface is no longer one million kilobits per second or one gig but rather 64k making it really bad then what r3 will do he'll pass on that information like oh here's the worst bandwidth in the path and then r2 will pass that onto r1 here's the worst bandwidth in the path so each of the downstream routers are going to use that worst bandwidth in the path as part of their composite metric calculation and one of the elements i'd like to share with you is that when a router like r4 is sharing information with r3 and r3 is sharing it with r2 and r2 with r1 that information regarding the worst bandwidth in the path and the sum of the delays up to that point that information is referred to as the advertised distance not to be not to be confused with administrative distance but the advertised distance in eigrp also sometimes referred to as the reported distance is the information among other things about the worst bandwidth in the path and from that perspective from that router who's advertising the sum of the delays from itself all the way to the destination network all right so here on r3 let's make sure in the right interface gig zero slash one let's do a bandwidth statement and we'll specify that we are going to do 64. i mean going from 1 million kilobits per second to 64. ah talk about bad news so what we also could do if you want to force this you could also do a shut of that interface wait a second no shut make sure then converges but right now what's happening is that bandwidth of 64 is being advertised as part of the information over to r2 and r2 is going to continue to propagate that information about the worst bandwidth in the path over to r1 in fact you know what i like to do let me show you a packet capture right here between r2 and r1 that shows that r2 is literally advertising that information about the worst bandwidth in the path and now that should show up as 64 kilobits per second and that's because r3 is reporting that as the worst path and r2 just propagates that information regarding the worst path and then r1 we'll use the 140 microseconds and the 64k in the calculation for its composite metric regarding the reachability of 10.4.0 all right so this was captured between r2 and r1 and so if we look at the payload in the ea grp payload of this packet which is an updated routing update here's the network 1040 that's being advertised we can expand that and scroll down i'll expand this part that's going to give us the details regarding the worst bandwidth in the path as well as a sum of delays up to that point and so here's the delays and so what's happening is r2 is advertising from its perspective that the delay is 130 microseconds and it's advertising that over to r1 it's also advertising here that uh bad news the worst bandwidth in the path is 64k so take that mr r1 and use that as part of your calculation for the metric going forward and we can verify that by going over to r1 and taking a look at the details of that route to verify that he believes that the worst bandwidth in the path is 64 and that the delay is 130 microseconds plus his own interface 10 microseconds which should be a total of 140 that we looked at just a few minutes ago so we'll go over to r1 and here on r1 this is the routing information for that network just a moment ago 140 microseconds and one gigabit per second we'll hit the up arrow key press enter and now it's showing the delay of 140 again because that didn't change from our last time but check this out instead of having a gigabit or 1 million kilobits per second is now using the value of 64k as the worst link in the path to get to that network and check this out the metric that it calculated previously was 6144 and now it's like was that 40 million yeah 40 million in change and that's because the minimum bandwidth in the path is just so terribly low that it makes it a really really terrible compared to the previous metric a much worse metric but you know at the end of the day if you do a show iprout you're gonna take the best path that you have and so there's our current route for the 10.4 network with that really really wacky big metric all right so now you know the truth about eigrp and the composite metric and here's what i would challenge you to do i would i would have you not just watch this video and say oh that's interesting especially if you're pursuing a ccna or ccnp because understanding ehrp is important for both of those certifications even though it's not explicitly listed in the blueprint items on the ccna exam so to help reinforce this go ahead download the packet tracer lab i'm using version 7.3.1 or newer would work as well the link for that free download is in the description of this video i'd like to have you download it take a look at it walk through this video again and use the packet facial lab to go through it step by step you'll get a better understanding of eigrp if you do also every sunday i think we have like dozens of them we have quizzes every sunday regarding cisco topics normally at the ccna level and one of those quizzes is all about eigrp so if you're asking yourself do i understand it well enough should i learn it more i would have you i'll put a link for that as well for the online quizzes just find the one on eigrp take a few minutes go through it have some fun and if you are not comfortable with any of those questions as far as eigrp goes in the quiz i would encourage you to dig a little bit deeper if you need support on eigrp or you want to have a chat with me or other people on the discord server that's also free the link is in the description below we would love to elaborate and talk about ea grp to make sure you are comfortable with it so to reinforce what i said at the beginning of the video surprises can be wonderful however if it's a surprise topic that you were not expecting in a certification exam not so wonderful so now you've been warned i've given you some tools to better understand ea grp and i wish you my friend the best of [Music] success you

Channel: Keith Barker

Views: 10,316

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Keywords: ccna, cisco, 200-301, Cisco CCNA, Cisco Certification, ogit, Keith Barker, packet tracer, packet tracer lab, eigrp routing protocol tutorial, eigrp configuration in packet tracer, eigrp protocol, eigrp ccna, eigrp packet tracer, eigrp ccnp, ccna certification, ccna 200-301, cisco ccna exam, cisco ccna lab, cisco ccna tutorial, 200-301 training, 200-301 exam, 200-301 ccna exam

Id: CHONDJ5Dgi4

Length: 23min 26sec (1406 seconds)

Published: Thu Sep 10 2020