Cisco CCNA ICND2 640-816

Routing Protocols: EIGRP Concepts and Configuration

by Jeremy Cioara

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Video Title Duration

Review: Rebuilding the Small Office Network, Part 1

Review: Rebuilding the Small Office Network, Part 2

Review: Rebuilding the Small Office Network, Part 3

Switch VLANs: Understanding VLANs

Switch VLANs: Understanding Trunks and VTP

Switch VLANs: Configuring VLANs and VTP, Part 1

Switch VLANs: Configuring VLANs and VTP, Part 2

Switch STP: Understanding the Spanning-Tree Protocol

Switch STP: Configuring Basic STP

Switch STP: Enhancements to STP

General Switching: Troubleshooting and Security Best Practices

Subnetting: Understanding VLSM

Routing Protocols: Distance Vector vs. Link State

Routing Protocols: OSPF Concepts

Routing Protocols: OSPF Configuration and Troubleshooting

Routing Protocols: EIGRP Concepts and Configuration

00:00:00 - We're now into the final routing protocol that we'll talk about
00:00:03 - in this CCNA video and that is EIGRP.
00:00:09 - EIGRP is CISCO's direct competition to OSPF.
00:00:13 - It is, unfortunately, proprietary. EIGRP is without
00:00:19 - a doubt in my mind the best routing protocol on the planet
00:00:22 - if you have CISCO routers everywhere and your corporate policy
00:00:26 - does not prevent you from using proprietary protocols. A lot
00:00:30 - of corporations really steer clear of that. So we are going to look at as we go
00:00:33 - into this video why I think that the good, the bad and the proprietary
00:00:37 - of EIGRP. We will then go into the configuration
00:00:40 - of EIGRP, look at features like auto summarization, how
00:00:44 - we can set up on our routers and will replace our whole network
00:00:46 - that's currently running OSPF with EIGRP.
00:00:49 - We'll even I believe go into some of the summarization features
00:00:53 - of EIGRP, just like we did with those OSPF; kind of
00:00:57 - take a step beyond CCNA and then we'll verify everything to make
00:01:00 - sure it's working correctly.
00:01:03 - Now EIGRP is the last routing protocol we're going to
00:01:06 - talk about so we have to answer the big question of why initially.
00:01:11 - Why would I use a proprietary routing protocol over OSPF or
00:01:16 - over RIP.
00:01:18 - Well first and foremost, EIGRP is the only routing protocol
00:01:22 - in the world that allows backup routes. Now I want to make
00:01:26 - sure I phrase that correctly.
00:01:29 - Backup routes are allowed by every routing protocol as in if
00:01:33 - this goes down it will fail over to this. But with
00:01:36 - EIGRP backup routes are remembered. Here's the idea. With
00:01:41 - OSPF, let's say OSPF or RIP. When they find the best way
00:01:46 - to get somewhere, they take that best way and they put into the routing
00:01:50 - table and then they forget about all the other paths that were
00:01:53 - once there, all of the back ups. So if the primary or the
00:01:57 - best way that's in the routing table goes down,
00:02:00 - OSPF and RIP have to rediscover or relook at the network
00:02:06 - to find all the backup routes and then find the best one of the backup
00:02:09 - routes and put that into the routing table. Not with the
00:02:12 - EIGRP. EIGRP uses backup routes in something known
00:02:17 - as the topology table. So whenever it finds the best way and
00:02:21 - that goes into the routing table, it says, oh yeah router; it
00:02:25 - speaks to itself. It says, if you ever lose that best
00:02:29 - away, I've got a perfect backup right here. So EIGRP is running along, life
00:02:34 - is good, the router is just sending packets, you know, humming along and all of a
00:02:40 - sudden wham, you know; a tractor outfront hit's the primary link to the internet.
00:02:43 - EIGRP detects the failure and immediately says shum.
00:02:48 - Here is the backup route, no real calculations are necessary,
00:02:52 - it just says I've got it right here because I tagged this as a backup
00:02:56 - route when we initially calculated the routing table. You
00:03:00 - can see that little dual algorithm there. Dual stands for diffused
00:03:04 - update algorithm. What it is, it is just the engine that runs
00:03:09 - EIGRP. With OSPF, the engine is known as SPF, it's
00:03:14 - the algorithm, that the guy who created OSPF, his name is
00:03:17 - Dijkstra created. The problem with OSPF and the SPF algorithm,
00:03:22 - is that it is very hard on your router's processor. So as your
00:03:26 - router is chunking out that routing table to find back a path, it is increasing
00:03:32 - the processor load on there. With EIGRP, dual is much
00:03:36 - easier on the processor and memory. So that's the number one
00:03:39 - reason why you choose EIGRP, the only protocol to remember
00:03:43 - backup routes. Second reason is that it's easy. CISCO's goal
00:03:48 - with the EIGRP was not to have a super complex protocol,
00:03:52 - but they wanted a protocol that could do all the same things
00:03:55 - as OSPF, but be easy. Meaning take the easy to
00:04:00 - configure aspects of distance vector like RIP. RIP was really
00:04:04 - easy to turn on. Take those features and combine them with
00:04:07 - all the advanced features of link state and get a simple
00:04:10 - config. Third reason you'd use EIGRP;
00:04:15 - flexibility and summarization. With OSPF, now think back what
00:04:21 - was the only place we could summarize in OSPF.
00:04:25 - At the ABR, at the area border router between areas.
00:04:30 - Well in EIGRP there is no concept of areas, because you can summarize
00:04:35 - whenever and wherever you want. I'll actually do that in this video
00:04:39 - as we get into the configuration, I'll show you, this is how we go
00:04:42 - under into interface and just throw in a summary route wherever one and technically
00:04:46 - I should say create an area boundary.
00:04:49 - Fourth, EIGRP is the only one that allows unequal costs
00:04:53 - to load balancing. Every protocol, even static routes, allow you
00:04:57 - to do equal cost load balancing, one packet here one packet there.
00:05:02 - EIGRP can actually take a network, analyze it and
00:05:05 - say well I've got, you know, say I've got two routes to
00:05:10 - the same network.
00:05:13 - Some routers, a little LAN over here and router 1 right here is trying to decide and
00:05:17 - over here it sees a T1 line, which is a 1.544
00:05:22 - megabits per second and over to the right up here,
00:05:26 - it sees half TI line, which would be
00:05:29 - 768 kilobits per second; that's exactly
00:05:33 - half of T1. Every other routing protocol in the world would say
00:05:36 - you are the best my friend and you go in the routing table. And
00:05:40 - this one which you see here is a backup, it will just be unused,
00:05:45 - thrown away. So that would be idle bandwidth that's just sitting there. Now
00:05:49 - with other routing protocols you can tune in and you could actually
00:05:52 - lie to the protocol and go into the interface and
00:05:55 - say the bandwidth of this interface is such and such and you know make
00:05:59 - it exactly equal to a T1 line and every other routing protocol
00:06:03 - would send one packet here and one packet here, but the problem
00:06:06 - with that is that it has to drag this T1 down to a
00:06:10 - 768k speed, so that it can equally distribute
00:06:14 - the load. So the point is you just can't load balance over
00:06:17 - unequal cost paths with other routing protocols. With
00:06:21 - EIGRP, you can set it up in such a way where you can
00:06:24 - type in a variance command and say, well I'll take a variance of two,
00:06:28 - which says exactly half. At that point, the router will load
00:06:34 - balance across links that are half as good as the primary.
00:06:38 - Now I don't want to get to deep into the variance command, but that will say,
00:06:41 - the EIGRP will say okay well I notice that I have a
00:06:45 - 768K link here and a 1544K
00:06:49 - link here or 1.544 megabit link. This is
00:06:52 - exactly half. So I'll send two packets on this link for every one
00:06:56 - that I send over here,
00:06:58 - on equal costs load balancing. By doing that you are effectively
00:07:01 - combining these into one logical link and using that bandwidth
00:07:06 - to its best, so the backup doesn't just sit there as idle bandwidth
00:07:09 - which you're paying for but not using.
00:07:12 - Five, I mentioned that are already, combines the best of distance vector.
00:07:16 - That's the easy to configure side of it and all the advanced
00:07:18 - feature of link state. Six and you've got to throw
00:07:22 - this in here.
00:07:24 - Supports multiple network protocols. I would say maybe eight
00:07:29 - years ago this was a cool feature, maybe even longer than
00:07:33 - that, back when we were using protocols like IPX/SPX
00:07:36 - and Apple Talk. EIGRP could support them all.
00:07:41 - Nowadays all we use is TCP/IP and that you know, I guess you could say it's still
00:07:46 - a feature but just hardly anybody uses it.
00:07:49 - Now let's get into how EIGRP works. EIGRP routers maintain
00:07:54 - three separate tables, a neighbor table, a topology table
00:07:59 - and a routing table.
00:08:01 - When you first start running the protocols, the neighbors will
00:08:04 - discover each other and just like OSPF, EIGRP discovers
00:08:10 - neighbors and uses the hello protocol or a hello message
00:08:13 - to say, hi are you online and exchange hello messages between
00:08:17 - them. Now EIGRP is not as strict as OSPF with what
00:08:22 - neighbors it can have, so it can more easily form neighbors,
00:08:25 - but once the neighbors are formed they will exchange routes.
00:08:28 - Now all of those routes go into a topology table and this
00:08:33 - is EIGRP's road map of the network. It will remember
00:08:37 - all of the best routes and all of the backup routes in that topology
00:08:41 - table as little flags. So for example, let's say
00:08:45 - well this network isn't very redundant, but let's say it is.
00:08:49 - We've got a link right here, so router 1 has two ways that it
00:08:54 - can get to the 10.1.2 network. The best route will
00:08:58 - go into the topology table and be marked as and this is
00:09:02 - getting in to some of the terms, a successor.
00:09:09 - Successor, that's like the primary route that is going
00:09:13 - to be chosen. And let's talk about the other table, that one
00:09:16 - gets moved into the routing table. That is the one that will
00:09:18 - be actively used by the router. Now router 1 also notices
00:09:23 - that it can go through router 2 and then through router 4 and
00:09:27 - get to this network. And it says, you know what, let's go in and
00:09:30 - add that guy into the topology table. So I'll have the
00:09:33 - 10.1.2.0 network over here and I will mark
00:09:37 - that one as a feasible successor.
00:09:43 - Now I know, I know that these terms can be kind of confusing
00:09:48 - at least for myself when I started
00:09:52 - thinking about them, let me finish writing there. Successor I almost think
00:09:56 - about like a throne and I think oh well the successor to the throne. So
00:09:59 - that would be a backup right. Well you have to kind of change the logic.
00:10:03 - The successor is the one who is, this is the way remember it,
00:10:07 - is succeeding; they're the best. You know, I am very successful
00:10:11 - you know, they're successful in what they do. So
00:10:15 - the successful one ends up in the routing table, that's the
00:10:19 - primary. Feasible successor is the one that stays in the topology,
00:10:23 - but it gets flagged; I put a little (b) here. It gets flagged as the
00:10:27 - backup. So if life is good and going along and all of a sudden wham the bomb
00:10:31 - hits and this this router 1 to router 4 link dies, this immediately
00:10:36 - drops out of the routing table as the successor because it's down,
00:10:40 - EIGRP says I've got that feasible successor and slide
00:10:44 - it right in there. With a little tuning,
00:10:47 - EIGRP can support something known as sub-second convergence.
00:10:52 - Meaning your network recovers in less than a second and
00:10:56 - it does take some tuning to get there, but that's the kind of
00:10:59 - level you can reach.
00:11:01 - Now let's get into configuring EIGRP. I have the
00:11:04 - same topology set up as I did when I configured OSPF, but now
00:11:09 - we're going to convert it to an EIGRP environment. So we'll start
00:11:12 - off on router 1 up here and the first thing I am going to do is go
00:11:16 - into router 1 and turn off OSPF; no router ospf one,
00:11:21 - good bye. I'll then go in and do router EIGRP; oops router
00:11:27 - EIGRP question mark, and you can see autonomous system
00:11:31 - number. Now you might remember with OSPF, this number was the process
00:11:37 - ID. In EIGRP this represents the system that you
00:11:42 - are in and unlike OSPF, it must be the same on all the routers
00:11:48 - in your network. So if I go in here and type in router
00:11:51 - eigrp 10, which I'll do right now, I have created the
00:11:55 - autonomous system ten and all the routers in my company have
00:11:59 - to be in that same autonomous system, otherwise EIGRP will
00:12:02 - say, oh you're not my company, I don't need to change routes with
00:12:06 - you. So once we're under the router EIGRP process, we
00:12:10 - turn on EIGRP in the same way that we do every
00:12:13 - other routing protocol. So I'm going to type in show IP interface brief,
00:12:17 - this is my internet router. I've got the 192.168.1.1
00:12:20 - and that's my internet link. I don't want to run
00:12:24 - EIGRP on my internet link or else you know I could form
00:12:27 - relationships with my internet service provider if they happen
00:12:31 - to run EIGRP. It would be very doubtful, but you never
00:12:34 - know. So I can type in network 192.168.1.0.
00:12:39 - Now remember,
00:12:43 - one of the criteria that CISCO wanted to meet, was they wanted
00:12:47 - to make this as easy to configure as RIP,
00:12:51 - but have all the advanced features that link state protocols
00:12:55 - have. So here we are at the network statements. If we were in
00:12:59 - RIP, this would be all we have to type; we hit the enter
00:13:02 - key and it starts running on any interface that starts with
00:13:05 - 192.168.1. You remember, think back, RIP
00:13:09 - you have to type in classfull networks. Meaning, whatever
00:13:13 - the default class of network is. So if I had 10.1.1.1,
00:13:18 - interface, I would type in my network as 10.0.0.0
00:13:23 - enter, because the 10 network is a class
00:13:28 - A network. Now right here I'm typing in network
00:13:32 - 192.168.1.0. It will work if I hit enter, but watch this.
00:13:35 - I hit enter and it says or hit question mark.
00:13:38 - I can either hit enter and just use it like I'm using RIP or
00:13:43 - I can allow wild card bits.
00:13:47 - Now wait a second, that's an OSPF thing. You better believe it and that's
00:13:51 - what EIGRP can do. You can go in and say I wanted to
00:13:55 - use it as simple as RIP or I want to use it you know with
00:13:59 - the complexity, and I should say complexity and flexibility
00:14:02 - of OSPF, because with OSPF you can really get specific as
00:14:07 - to what interfaces you would like to enable EIGRP on. So
00:14:11 - I hit enter and I am done. EIGRP is now sending hellos out
00:14:16 - to the 192.168.1 interface up here at router
00:14:20 - 1. Let's hop down to router 2.
00:14:25 - Router two, I am going to get into global config mode. You want to know
00:14:28 - something, you can't hear me type anymore, can you.
00:14:32 - That's because my wife bought me a brand new keyboard. It's
00:14:36 - awesome, it's an Apple keyboard. Have you seen these things,
00:14:40 - these things are like razor thin and you can, literally they are
00:14:45 - super thin and you cannot hear me type. You know it was, I'm sure
00:14:49 - a little selfish motivation on her part not to throw her under
00:14:53 - the bus. I am sure she had a great heart and everything. But when I'm in
00:14:56 - here and I'm a typing, I'm slamming on the that keyboard and it's loud and she's
00:15:00 - oh you type so loud come on, and so this keyboard you can't
00:15:03 - hear me anymore.
00:15:05 - Anyhow, so I am going to type in, no router ospf 1. I'm turning
00:15:09 - off OSPF, killed the neighbor. Now I am going to type in router
00:15:13 - EIGRP 10, to be in the same autonomous system. On this
00:15:17 - one let's do a show IP interface brief and there's my
00:15:22 - 192.168 network. So I'll do network 192.168.0.0, question mark,
00:15:26 - and there's my option for
00:15:29 - wild card bits. Oh that's so helpful. If I were using this with
00:15:33 - a RIP, I would have to type in a unique network statement for every
00:15:36 - single one of these; 192.168.1.0 enter,
00:15:39 - 192.168.10.0 enter,
00:15:42 - 192.168.20.0 enter. Here I can just say
00:15:46 - 192.168.0.0.0.0.255.255,
00:15:50 - which again says I care about 192; I care about 168;
00:15:56 - I do not care what comes after that. So I will automatically
00:15:59 - run EIGRP on every interface starting with
00:16:03 - 192.168 and right there we can see a neighbor
00:16:06 - relationship has formed, a new adjacency. I am going to type in
00:16:10 - show ip eigrp neighbors.
00:16:17 - You have to spell neighbor. Okay, I'll go back and do a show, hang on;
00:16:23 - show ip; I spelled EIGRP wrong,
00:16:30 - eigrp neighbor. It must be this new keyboard.
00:16:34 - Alright so there we go, we've got the neighbor, we see the address
00:16:38 - 192.168.1.1, that's our router 1. I can
00:16:41 - see the interface I formed a neighbor on, I can see how long
00:16:44 - that neighbors' been running, I can see the whole time; whole time is
00:16:48 - how long it believes until that neighbor is dead.
00:16:52 - By default, EIGRP says hello once every five seconds.
00:16:56 - So if the neighbor stops saying hello for any amount of
00:17:00 - time, you notice that the hello timers 11 seconds, 10 seconds, oh
00:17:03 - backup to 14, that's because this guy is saying hello once
00:17:07 - every five seconds. Hello, as soon as this guy receives a hello, it's starts the countdown.
00:17:12 - It says if I don't hear another hello from you in 15 seconds, a.k.a. Hold
00:17:16 - down timer, you are considered dead and I will no longer use your
00:17:19 - routes and that's why you should never hopefully see this hold
00:17:23 - timer go below 10, because if it does that means you're missing
00:17:28 - hellos. You see it go down to 10 and back up because it received
00:17:31 - another hello. SRT, I won't get too deep into this stuff, but
00:17:35 - that stands for source round trip timer, that's how long it
00:17:38 - takes to get to the neighbor and back. And that helps
00:17:41 - gage how long it should be waiting before it expects a hello.
00:17:44 - Now over here H,
00:17:48 - that is the most unknown column to anybody in EIGRP.
00:17:53 - I challenge you to find what does H stand for and I'm serious.
00:17:58 - Nobody really knows. I can tell you what that column is, it
00:18:02 - is a list of the neighbors and the order it was received.
00:18:07 - So for example, if router 2 gets another neighbor, which it will,
00:18:10 - it will be H1 or and then two more neighbors will be
00:18:14 - H2 and H3. Those are the order it learned about the neighbors,
00:18:17 - but nobody knows what H really stands for. I know somebody suggested
00:18:21 - hop count, but hop count, your neighbor can only be one hop
00:18:26 - away or no hops away otherwise you're not neighbors,
00:18:29 - you're remote distant cousins. So anyway mystery; hop.
00:18:34 - So I am going to go over to router 3, let's get that guy running;
00:18:38 - no router ospf 1, we are killing that guy, router eigrp 10, go into there;
00:18:43 - network and let's check out router 3.
00:18:50 - Okay he's 192.168.3 and 2. So I'll
00:18:54 - , let's do 192.168.0.0
00:18:58 - and we'll use the wild card bat bits. That gets
00:19:02 - it running on all the 192.168 networks and
00:19:05 - poof it forms a neighbor, that's fantastic. And this one is
00:19:08 - the one that has all the loop back interfaces. So we can
00:19:11 - advertise those as well and that way I can also show you summarization with
00:19:15 - the EIGRP.
00:19:16 - Let's do network, 172.30.0.0
00:19:20 - and we'll add in 0.0.255.255 as our
00:19:24 - wild card bits, so it automatically runs on all of these interfaces
00:19:27 - and advertises them to the rest of the network. Super, so at
00:19:31 - this point I should be able, well I'll stay on router 3 to do a show
00:19:35 - ip eigrp neighbor
00:19:38 - and there's my neighbor I learned about. This is router 2 that
00:19:41 - is router 3's neighbor. I can do a show ip route and I
00:19:45 - should be learning at this point D routes, D as in dog.
00:19:51 - D stands for EIGRP, because E was already taken by
00:19:55 - the external or EGP external gateway protocol. So CISCO
00:20:00 - said well let's use D. So all routes learned by EIGRP
00:20:04 - is going to be represented with a D.
00:20:09 - Now you can see right here 192.168.20.0,
00:20:13 - 192.168.1.0 are all in the table and there's
00:20:16 - all my loopbacks and so on, but I want to show you something.
00:20:20 - Let me show you something. I am going to go over to router 2. I am going to do a show
00:20:26 - ip route, prepare yourself.
00:20:31 - Wait a second, where's all the loopbacks? 192.168.30.5 and four and seven
00:20:35 - where did they all go.
00:20:41 - Ah, hah. Look at that guy, 172.30.0.0/16.
00:20:45 - What we have experienced is my least favorite feature
00:20:51 - of EIGRP. It is a feature known as auto summarization.
00:20:57 - What EIGRP does, is any time you have a network that
00:21:02 - is advertised across a boundary that is not the same network,
00:21:06 - it will auto summarize. Let me give you an example of that.
00:21:10 - Right here I have a network, it is a class B,
00:21:13 - 172 dot; oh I still need to fix that. Good grief, it's
00:21:17 - 172.30 networks, right. You guys have seen
00:21:21 - that. Wow I just moved up my screen a little bit but that's alright; 172.30.0.0,
00:21:27 - that's the network said this
00:21:30 - represents. That's a class B network and that one class of addresses.
00:21:34 - Now up here I have a class C network, 192.168.2.
00:21:39 - Remember class C addresses start with 192 and that goes to
00:21:42 - 223, so it's a class C network. Over here class C network.
00:21:47 - So when I advertise some, it's actually technically called
00:21:52 - a discontinuous network, a network that is not of the same
00:21:55 - type or same class as this network across
00:21:58 - that boundary. EIGRP thinks it's doing me a favor and
00:22:02 - it will say; Well I'll tell you what, I'll auto summarize that back
00:22:07 - to its default class B boundary. Remember by default,
00:22:11 - 172.30 is a class B network.
00:22:19 - Let's get my screen moved up here. It's a class B network, so it
00:22:24 - will auto summarize back as if it was a class B network all
00:22:28 - over again, that's a class B subnet mask. Now I don't like that feature.
00:22:33 - Whenever I hear anything in auto, in CISCO that's auto,
00:22:36 - I think I auto not use that. No auto feature is good
00:22:40 - or I should say very very few of them are. Now let me give
00:22:43 - you another example. Up here in router 1 I had
00:22:47 - 10.1.1.0/24 and 10.1.1.2.0 and
00:22:51 - and 3.0. Now I've subnetted those
00:22:54 - with classy subnet masks, but when they are advertised over here
00:22:58 - this is a discontinuous network. I am not advertising it over
00:23:01 - another 10 network, so EIGRP would auto summarize
00:23:05 - back to this 10.0.0.0/8, because it thinks it
00:23:12 - is doing me a favor and just auto summing them up. Now some people
00:23:15 - like that and that it's very distance vector protocolish to
00:23:18 - do something like that, there's other protocols that do that
00:23:20 - like RIP, but I don't like that. I like control over where my
00:23:24 - summary routes go because you know what, I could come up with
00:23:27 - a much better summary route than 172.30.0.0/16
00:23:31 - because if I use that it kills the whole
00:23:34 - 172.30 range; because all these routers believe
00:23:38 - router 3 has everything to do with 172.30.
00:23:41 - So I am thinking I need to turn off that feature and
00:23:45 - here is how you do it.
00:23:48 - Holy cow, was I typing in, you can see what I was typing in for a little bit.
00:23:53 - Forgive me, I hope not; I've got to review this video and make sure
00:23:57 - it looks okay. Okay, so where was I?
00:24:03 - Oh, auto summarization. The way that we turn it off, router
00:24:06 - eigrp 10; is I can type in no auto summary. I just think
00:24:12 - no auto, no auto that's what we need to type. It resets
00:24:16 - the neighbor relationships and will reform them, says summary
00:24:19 - reconfigured. I am going to go up to router 1. Router eigrp, got
00:24:23 - to do on all of them, no auto; router 3,
00:24:27 - router eigrp 10, no auto, turn that off on all of
00:24:32 - them, no auto summary. So that will
00:24:35 - reform all those neighbor relationships and now look what happens.
00:24:38 - I go over router 2 and I see, I do a show ip route,
00:24:44 - and I am now getting all the more specific routing information
00:24:48 - from that router. It does not auto summarize that into
00:24:51 - 1/16 block, that's good.
00:24:54 - Now let me go back and show you how I can inject a manual summary
00:24:59 - route. I had to pause the video there for a moment, to make sure I didn't
00:25:01 - cut anything off from my screen. It jumped around and I didn't, that's good.
00:25:07 - So I'm going to go to router 3 and actually let me stop
00:25:11 - right there and first mention, if you are a CCNA candidate
00:25:14 - I have talked about everything you need to know for CCNA.
00:25:18 - For the EIGRP, I am about to show you a cool CCNP concept,
00:25:21 - but again very simple and it's a way that you can make your
00:25:24 - network much more efficient. I am going to go on, we're going
00:25:28 - to the place where all those routes came from; router 3.
00:25:32 - Show ip route, I can see that I've got all those directly connected,
00:25:35 - 172.30.6. Now you remember if you watched the
00:25:39 - OSPF videos, that I was able to summarize at the ABR.
00:25:43 - In the EIGRP I can summarize it anywhere. All I need to do
00:25:47 - is go under the interface that I want to send the summary route
00:25:51 - out of. So on router 3 I want to go underneath serial 0/0,
00:25:56 - because that's where I'm going to be sending the summary route
00:25:59 - out of.
00:26:00 - I am going to go serial 0/0 and I am going to type in ip eigrp; oh hang on,
00:26:12 - ip, wait a second.
00:26:15 - I jumped ahead of myself, ip summary address, good old
00:26:20 - context instead of help. For EIGRP, that's the protocol that I want
00:26:24 - to do. What autonomous system? Autonomous system 10.
00:26:28 - Do question mark and it says what do you want your summary route to
00:26:30 - be. I'll do 172.30.0.0. Now in the
00:26:35 - last video on OSPF, we figured out the best summary
00:26:39 - mask for the 172.30 networks would be
00:26:43 - 255.255.248.0 and that would
00:26:47 - summarize zero through seven. Now I know we added eight in there
00:26:51 - and we'll see how EIGRP handles that.
00:26:54 - I'll put 255; it's going to hit the question mark, 255.255.248.0,
00:26:58 - it's asking for that summary mask. Now I'll do
00:27:02 - space question mark and if you want you can tune the administrative
00:27:05 - distance, which is the believeability of that summary route. I don't
00:27:09 - need to do that so I'll hit enter and now it's going to create
00:27:13 - this neighbor change. It kind of downs the neighbor and comes back up
00:27:16 - and says a new summary is configured, new adjacency is brought
00:27:19 - up. I am going to do, go over to router 2 now and do a show ip route.
00:27:25 - Look at that, there's my new summary route that encompasses zero
00:27:29 - through seven and it automatically advertises eight as a separate
00:27:33 - network because it realizes that's not encompassed in my summary
00:27:35 - route. Now I want to show you one more thing
00:27:40 - and this is going to be a massive concept. What I
00:27:43 - mean is how this affects your knowledge of routing, not
00:27:48 - so much a big unbelieveable concept. Right here we go. Look at
00:27:53 - that. You see in the router that is sending the summary route,
00:27:57 - it says I have 172.30.0.0 that is a summary route
00:28:01 - that I typed in and I'm sending all traffic that is sent to
00:28:04 - that summary route to Null0.
00:28:08 - Null0 is the garbage can. What? That means any traffic that
00:28:14 - it gets that matches this summary route, the router is going to
00:28:18 - automatically send to the garbage can. It's going to drop that
00:28:20 - traffic. Now why would it do something like that, well
00:28:25 - thing about this. All of these routes have a very specific subnet
00:28:29 - mask /24. When we create a summary route,
00:28:33 - let me put that up here 172.16.0.0/21,
00:28:37 - that's our summary route, that encompasses zero through seven.
00:28:41 - What if this one didn't exist, what if our router, router 3
00:28:46 - had 172.30.0.1.2
00:28:51 - three, five, six and seven and we said oh well that's alright; let's
00:28:54 - just create a summary route for all of those and, you know,
00:28:57 - we'll just not use dot 4 anywhere. Well the way EIGRP
00:29:01 - works is if they gets a packet for the 172.30.4
00:29:05 - network, it will start asking other routers with these
00:29:08 - things known as query packets and it will say other routers can
00:29:11 - you find a way to the dot 4 network and they will say I don't know.
00:29:14 - They will start searching the whole network causing all this traffic to try and
00:29:18 - find a route to a network that doesn't really exist. So what
00:29:21 - this Null0 route does, is it says you know what if you
00:29:26 - get a packet for something you don't have a more specific route
00:29:30 - for then threw it away.
00:29:33 - Here's what I mean, you've got all of these routes in the routing
00:29:36 - table. Notice this one, six, seven and the router organized these at
00:29:42 - its own will, whatever it thinks it's going to use first.
00:29:45 - So we've got this organization right here. These are all
00:29:47 - more specific subnet masks. Rule number one of routing, it doesn't
00:29:53 - matter what routing protocol you have, what you're running, is
00:29:56 - if it has a more specific subnet mask, it will use that.
00:30:01 - So here's what I mean. Router 3 gets a packet from 172.30.3.50,
00:30:04 - looks at it's routing table and says
00:30:07 - ah 3.0, I've got a match. Needs to go out and loopback 3
00:30:11 - interface, but then it looks and says, oh wait, I've got another
00:30:14 - match 172.30.0.0/21, that
00:30:17 - includes 3.50. That really represents zero zero through
00:30:21 - seven dot 255. So 3.50 is included in
00:30:24 - there. So it looks and goes well I am not going to use that one because I have a more
00:30:29 - specific route. The better the subnet mask, the more specific the subnet
00:30:33 - mask, the better the routers. So this will never be used as
00:30:37 - long as it has a more specific route right here.
00:30:41 - The only time you will actually use this route to the garbage can,
00:30:44 - is if one of these more specific routes that don't exist and
00:30:47 - that means the network doesn't exist. So that's the idea behind
00:30:52 - that Null0 route and that idea of specificity in those
00:30:55 - subnet masks is big.
00:30:58 - That is the core of the EIGRP routing protocol. As you
00:31:02 - can see EIGRP is far easier to configure than OSPF
00:31:09 - in multiple areas and all those kind of things and as you get into
00:31:12 - the more advanced CCNP curriculum, you will even see that ease
00:31:15 - come out more and more, that ability to summarize on any interfaces
00:31:19 - is a big one when you're looking for good features in a routing
00:31:22 - protocol. So we saw the reasons that you would look at EIGRP
00:31:26 - as a good replacement for your organization. That was the
00:31:30 - fact that it never throws away routes. You can summarize at any
00:31:33 - point in the network, the algorithm it uses, which is known as DUAL, is
00:31:37 - far more efficient than the OSPF routing protocol
00:31:41 - and it is the only one I can load balance over on equal
00:31:44 - cost paths. We saw EIGRP auto summarization, which is
00:31:49 - a feature that I don't like. EIGRP
00:31:52 - will summarize networks back to their classfull boundary
00:31:57 - any time you advertise them across a discontinuous link. The best
00:32:01 - thing you can do for your network is to go in and type in
00:32:03 - no auto and put in manual summary routes wherever you need. Last but
00:32:08 - not least in no specific order, we saw the EIGRP configuration
00:32:12 - and verification. Simple commands router EIGRP and the autonomous
00:32:16 - system followed up with your networks, verified by doing a
00:32:19 - show ip eigrp neighbors and show ip route. I hope that this
00:32:25 - has been informative for you and I'd like to thank you for viewing.

Access-Lists: The Rules of the ACL

Access-Lists: Configuring ACLs

Access-Lists: Configuring ACLs, Part 2

NAT: Understanding the Three Styles of NAT

NAT: Command-line NAT Configuration

WAN Connections: Concepts of VPN Technology

WAN Connections: Implementing PPP Authentication

WAN Connections: Understanding Frame Relay

WAN Connections: Configuring Frame Relay

IPv6: Understanding Basic Concepts and Addressing

IPv6: Configuring, Routing, and Interoperating

Certification: Some Last Words for Test Takers

Advanced TCP/IP: Working with Binary

Advanced TCP/IP: IP Subnetting, Part 1

Advanced TCP/IP: IP Subnetting, Part 2

Advanced TCP/IP: IP Subnetting, Part 3

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Jeremy Cioara

Jeremy Cioara

CBT Nuggets Trainer

Certifications:
Cisco CCNA, CCDA, CCNA Security, CCNA Voice, CCNP, CCSP, CCVP, CCDP, CCIE R&S; Amazon Web Services CSA; Microsoft MCP, MCSE, Novell CNA, CNE; CompTIA A+, Network+, iNet+

Area Of Expertise:
Cisco network administration and development. Author or coauthor of numerous books, including: CCNA Voice 640-461 Official Cert Guide; CCNA Voice Official Exam Certification Guide (640-460 IIUC); CCENT Exam Prep (Exam 640-822); CCNA Exam Cram (Exam 640-802) 3rd Edition; and CCNA Voice 640-461 Official Cert Guide.


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