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Cisco CCNP TSHOOT 642-832

Route TSHOOT: BGP Concept Review

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Video Titles Duration
1. TSHOOT: Setting Your Expectations
2. General TSHOOT: The Troubleshooting State of Mind
3. General TSHOOT: Troubleshooting Before You're Treading Water - Proactive Steps
4. General TSHOOT: Troubleshooting Before You're Treading Water - Proactive Steps, Part 2
5. General TSHOOT: IOS Tools to Monitor and Maintain the Network
6. General TSHOOT: IOS Tools to Monitor and Maintain the Network, Part 2
7. Switch TSHOOT: VLANs and Spanning Tree Concept Review
8. Switch TSHOOT: VLANs and Spanning Tree
9. Switch TSHOOT: VLANs and Spanning Tree, Part 2
10. Switch TSHOOT: L3 Switching and Redundancy Protocols Concept Review
11. Switch TSHOOT: L3 Switching and Redundancy Protocols
12. Switch TSHOOT: L3 Switching and Redundancy Protocols, Part 2
13. Route TSHOOT: L3 Connectivity and EIGRP Concept Review
14. Route TSHOOT: L3 Connectivity and EIGRP
15. Route TSHOOT: L3 Connectivity and EIGRP, Part 2
16. Route TSHOOT: L3 Connectivity and EIGRP, Part 3
17. Route TSHOOT: OSPF and Route Redistribution Concept Review
18. Route TSHOOT: OSPF and Route Redistribution
19. Route TSHOOT: OSPF and Route Redistribution, Part 2
20. Route TSHOOT: BGP Concept Review
21. Route TSHOOT: BGP
22. Route TSHOOT: Router Performance Issues Concept Review
23. Route TSHOOT: Router Performance Issues
24. Security TSHOOT: Access List Concept Review
25. Security TSHOOT: Access List Chaos
26. IPv6 TSHOOT: IPv6 and IPv6 Routing Protocols

TSHOOT: Setting Your Expectations

General TSHOOT: The Troubleshooting State of Mind

General TSHOOT: Troubleshooting Before You're Treading Water - Proactive Steps

General TSHOOT: Troubleshooting Before You're Treading Water - Proactive Steps, Part 2

General TSHOOT: IOS Tools to Monitor and Maintain the Network

General TSHOOT: IOS Tools to Monitor and Maintain the Network, Part 2

Switch TSHOOT: VLANs and Spanning Tree Concept Review

Switch TSHOOT: VLANs and Spanning Tree

Switch TSHOOT: VLANs and Spanning Tree, Part 2

Switch TSHOOT: L3 Switching and Redundancy Protocols Concept Review

Switch TSHOOT: L3 Switching and Redundancy Protocols

Switch TSHOOT: L3 Switching and Redundancy Protocols, Part 2

Route TSHOOT: L3 Connectivity and EIGRP Concept Review

Route TSHOOT: L3 Connectivity and EIGRP

Route TSHOOT: L3 Connectivity and EIGRP, Part 2

Route TSHOOT: L3 Connectivity and EIGRP, Part 3

Route TSHOOT: OSPF and Route Redistribution Concept Review

Route TSHOOT: OSPF and Route Redistribution

Route TSHOOT: OSPF and Route Redistribution, Part 2

Route TSHOOT: BGP Concept Review

00:00:00 - Well, it's time to visit our final routing protocol, the big
00:00:04 - grizzly protocol so known as BGP. BGP is awesome. It's one of
00:00:09 - those protocols you can never reach the end up. So what I want
00:00:12 - to do in this section is again get our blood flowing before we
00:00:15 - get into troubleshooting. Look at just kind of a big picture
00:00:18 - concepts of BGP and then some key troubleshooting tips.
00:00:22 - All right, well let's start off with the place of BGP and it's
00:00:26 - not always where everybody expects. Now you're at the end of
00:00:29 - your CCMP journey so you have a pretty good idea of what BGP
00:00:32 - is, I'm assuming, which it is the routing protocol of the internet.
00:00:37 - ISP is everywhere, exchange their internet routing tables using
00:00:40 - BGP but you also know that BGP is one of the slowest routing
00:00:45 - protocols on the planet by design. It's in, it's funny when talking
00:00:49 - to CCNA's people, people are just getting into the networking,
00:00:52 - you bring up BGP and they go, "Oh what's that." You go, "Oh,
00:00:55 - it's a routing protocol of the internet." And immediately their
00:00:58 - mind goes, "Wow, that must be really good, really fast, really",
00:01:02 - I mean like all of these preconceived notions because of course,
00:01:05 - the internet is so big you have to have a really crazy big protocol
00:01:07 - to run it, which it is true. BGP is crazy big, no doubt. But
00:01:13 - it is not fast but it's really slow by design because when you
00:01:17 - have a network the size of the internet, you can have rapid fire
00:01:21 - updates that go across the internet and tie a network goes up
00:01:24 - and down. So, it's not the ideal protocol for internal use. It's
00:01:29 - meant for external use. Now BGP is typically used between internet
00:01:33 - service providers but larger companies or companies that deal
00:01:36 - with multiple internet
00:01:39 - service providers find BGP very handy to allow themselves to
00:01:44 - advertise their own block of addresses. So maybe this company
00:01:47 - right here hosts a website or has an email server or whatever.
00:01:51 - They want something that's available through multiple service
00:01:54 - providers. Here's ISP1
00:01:57 - and ISP2. Well, outbound access is easy. All you have to do is
00:02:03 - setup a default route and you could say, okay well, this is we'll
00:02:05 - say the preferred, you know, my primary path and this is my backup.
00:02:09 - Or you can even set up if you got equal cost internet connections
00:02:13 - or equal internet connections, you can set it up to where it'll
00:02:15 - load balance between those out bound without a problem. It's
00:02:18 - the inbound stuff that gets pretty complex and harry, because
00:02:23 - you got, we'll say, let's just say that
00:02:28 - sub net.
00:02:30 - You're advertising out to the world. Well, when you advertise
00:02:33 - that out to both ISPs you're going to get traffic that comes
00:02:37 - in, it's low balance between, you know, those kind of but not
00:02:41 - really you have to tweak how the distance of this and you have
00:02:45 - to make sure that this address block is independent meaning neither
00:02:48 - ISP is claiming it for themselves like they're the owner of those
00:02:51 - so you have independent address spaces. There's a lot of complexity
00:02:55 - that deals with having your own address space and handling redundancy
00:02:59 - with BGP but that's one of the uses of BGP. But let me broaden
00:03:03 - your mind a little bit because larger organizations uses BGP
00:03:06 - for not just internet connectivity. I just, I was just dealing
00:03:10 - with the whole network team from a, I'll just say a credit services
00:03:15 - group. It's a well known credit card company. If I said the name,
00:03:19 - you would recognize it and I was talking with their group and
00:03:22 - I say, "Well, how are you using your network? How was your network
00:03:25 - designed?" And they said, well internally it's just a bluff,
00:03:28 - I mean we've got OSPF running internally. We've got the EIGRP
00:03:33 - between another group. We're redistributing between those guys
00:03:36 - and he said, we even have RIP in some areas of the network because
00:03:39 - some of our mainframe systems only support the RIP protocols.
00:03:42 - He said, we have every routing protocol under the sun but we
00:03:45 - also use BGP, not just for internet connectivity. They use BGP
00:03:51 - to the internet but they also have partner organizations. I'll
00:03:54 - just put partner A over here which might be a credit processing
00:03:58 - firm, partner B which might be another credit card company I
00:04:02 - said B but I wrote A so we've got all these partners and so what
00:04:05 - they wanted is they wanted to be able to hand out routes to those
00:04:09 - companies and accept routes from those companies within controlled
00:04:14 - limits. BGP allows you to do that. So, one of the only routing
00:04:18 - protocols that does not trust neighbors. You actually have to
00:04:22 - manually configure your neighbors and then you can put very very
00:04:26 - tight filters on exactly what route you send your neighbors and
00:04:31 - what routes you accept from them. So BGP is awesome when it deals
00:04:35 - with controlling what routes you're allowing inside and outside
00:04:38 - of your company. All these other protocols, OSPF, EIGRP and RIP
00:04:42 - they're super, well except RIP. They're super for internal route
00:04:47 - exchange because everybody is trusted, everybody just exchanges
00:04:49 - route and it just works internally by default but when you really
00:04:53 - want control, that's where BGP comes in. Okay.
00:04:56 - So let's roll down into the facts about
00:05:00 - BGP. BGP is one of the, well, it's the only
00:05:05 - internal thing, I think-- I think it's the only protocol that
00:05:09 - runs, routing protocol that runs on top of TCP. All the other
00:05:12 - protocols, OSPF, EIGRP, RIP RIP uses UDP. EIGRP and OSPF have
00:05:18 - their own little reliability mechanism. They are their own protocol.
00:05:20 - They don't use TCP or UDP. So BGP being that it's slow and clunky,
00:05:25 - when you really get down to it, it's a let's go and use TCP three
00:05:30 - way handshakes, we'll use TCP keepalives as kind of our hello
00:05:33 - message, if you will. So it really relies on TCP to ensure the
00:05:38 - underlying network fabric is working okay between the BGP neighbors.
00:05:44 - So TCP is one of the core pieces of BGP. Updates,
00:05:48 - of course are incremental and triggered. It would just be madness
00:05:53 - if BGP would send an update anytime a change occurred because
00:05:56 - in a routing table the size of the internet, you're always seeing
00:06:00 - routes goes up and down, up and down and all kinds, I mean a
00:06:03 - hundred of changes to the table happen every instance. So in
00:06:06 - BGP we're going to say, oh, oh, let me send that, right away.
00:06:09 - Okay. Let me get that. It would just bug the whole thing down
00:06:12 - and thus this talks about why BGP is so slow. It is because it's
00:06:17 - impossible to have rapid fire triggered updates, it's just going
00:06:20 - to go ahead and receive all the updates and whenever it reaches
00:06:23 - its increment, then it will send all the updates at once to its
00:06:27 - neighbors and I kind of describe it like you know, a router receives
00:06:31 - an update and say, "Oh thanks for that. It's nice. Let me just
00:06:35 - kind of sit on that for a little while. Oh, here's another. Okay.
00:06:37 - Let me sit on that." And then once it reaches its timer, it says,
00:06:40 - "Okay, well let me tell this to all of my neighbors. And so it's
00:06:44 - often used DNS as a good comparison you know, where you add in
00:06:49 - a DNS entry to an internet name server and then it replicates
00:06:52 - to its DNS peer on a time interval. So it takes a long time
00:06:56 - for a route domain name to show up in the internet DNSS, a kind
00:07:00 - of same style of concept with BGP but maybe not quite as long.
00:07:06 - So you're probably looking at that forth bottom bullet, I'm not
00:07:09 - even going to go there. Guys, I was like, do I go to the metric
00:07:13 - of BGP and I thought, no way. Shoot on back to the route series
00:07:18 - in the CCNP, meaning, you might remember that, that list, I think
00:07:22 - it's about 10, 11 different I think it's 10 attributes that BGP
00:07:25 - uses to figure out the best way around the network where it says,
00:07:28 - "Okay, what's the highest weight?" Figures that out on the space
00:07:32 - on it. Okay, let me check the local preference and it just keeps
00:07:35 - going down to this list. The big tie breaker that most of the
00:07:39 - time breaks the tie is the autonomous system path which is why
00:07:42 - BGP by default is no better than RIP in many senses because you've
00:07:47 - got you're autonomous systems right here. Will say it's AS, just
00:07:50 - say 100 connecting to this guy and this guy, this guy and all
00:07:54 - these autonomous systems all around the internet and you're trying
00:07:58 - to find the best way to get to this autonomous system up here.
00:08:02 - By default most of the metrics ties to the BGP says, "Well, I
00:08:06 - can go through this autonomous system, two, three, and I'm there
00:08:10 - or I go, okay, one, two, three and eight, well, of course my
00:08:14 - diagram would be a tie." But you get the idea. It uses autonomous
00:08:18 - systems like hops and finds his way around the network that way,
00:08:21 - which is just kind of a random roll of the dice. So that's one
00:08:25 - of your big jobs when you get BGP as tweaking the metric for
00:08:29 - the routes that really matter. So you make sure you uses the
00:08:31 - best exit point. So and I mentioned this, it is the slowest routing
00:08:35 - protocol in the planet to converge by design. As
00:08:39 - we get ready to dive in to the troubleshooting and so my key
00:08:42 - tips for you when you do trouble shooting, let's look at the
00:08:45 - packets and tables that build BGP, kind of behind the scene,
00:08:49 - what does it use. Well, it's nice because BGP despite its massive
00:08:55 - scope and complexity when you get to the route maps and modifying
00:08:58 - your attributes of BGP and your metrics, really it's simple when
00:09:04 - it comes to the communication. You've got four types of packets
00:09:07 - that it sends. You've got yours open which says, "Okay, I want
00:09:11 - to start this session." Now keep in mind all of these, I'm just
00:09:14 - skipping the right by TCP, all right. TCP does its thing. You
00:09:17 - got the scene, the scene act, the act where negotiating our session.
00:09:20 - So assuming TCP does its thing, the next packet that's going
00:09:24 - to come would be an open message. And the open message is going
00:09:27 - to say, "Hey Bud, I'm BGP, let's be neighbors. I'm configured
00:09:31 - to talk to you, let's talk." So it's going to come back from
00:09:36 - the, well I should say the neighbors is going to receive that
00:09:39 - open messages and say, well, okay let's see if all of the criteria
00:09:43 - match? Am I configured to speak to you as a neighbor? Do I have
00:09:47 - EBGP multi app?" All of the configuration settings that BGP is
00:09:52 - required to do is compared in that open message. Assuming all
00:09:56 - of those agree, they become neighbor. And then from there, they
00:09:59 - are going to start sending update messages to each other. "Hey,
00:10:02 - I know about this, I know about this, let's exchange our BGP
00:10:04 - tables." All of that exchange happens, life is good, from there
00:10:09 - on now all that's going to be sent is keepalives, but just duh!
00:10:13 - That's TCP keepalive, it keeps the session alive. Make sure that
00:10:17 - the neighbor stays online. So if TCP fails, then your neighbor
00:10:20 - fails and then on that triggered interval,
00:10:24 - whatever interval you decide to set, it's going to send updates
00:10:29 - so that would be you know, anytime something changes in the BGP
00:10:32 - routing table. You don't want to see notification messages.
00:10:36 - That's usually you think, well what kind of notification? You
00:10:39 - know that's just a message. It's like notification that means
00:10:42 - something bad happened. So you know, something maybe you tore
00:10:45 - down a neighbor, you shut down your neighbor, something like
00:10:48 - that. It's going to send a notification and just letting the
00:10:50 - other guy know, "Hey, I'm going down, go ahead and tear down
00:10:53 - the session, TCP is limited and all that. Now obviously, if you
00:10:56 - lose network connectivity you're not going to get notifications.
00:11:00 - TCP is just going to die eventually, the keepalives fail and
00:11:03 - then by the time it's said and done, you will, I hate that
00:11:09 - when that happens. You ever heard that happen? You're just going
00:11:12 - going and all this in your brain is like, I'm thinking about
00:11:14 - the Easter bunny. Actually I know why it happened. I've got,
00:11:17 - my Easter is right around the corner for us and my Aunt bought
00:11:23 - my daughters this little bunny that they push a button on the
00:11:27 - bunny and it's really quite amazing, the first time you see it.
00:11:30 - That's not a bunny. That's like, some kind of little devil or
00:11:34 - something but it's got this little bunny right here. That's kind
00:11:37 - of how I think about the bunny. You push the button on the little
00:11:40 - mitten and its ears start clapping and it sings, If You're Happy
00:11:44 - and You Know It. So it's very loud and its ears are always clapping,
00:11:47 - so that's exactly what happened as I hear this bunny begin singing
00:11:51 - and I, exactly, right here. Something bad has happened. My brain
00:11:54 - is like bunny happy if I know and it just blanked out. So what
00:11:57 - was I talking about? TCP, oh yes. Okay, so if the network connection
00:12:02 - goes down, right, TCP is going to fail. You're not going to see
00:12:05 - a notification message. It's just going to see, "Okay, TCP has
00:12:08 - failed. I'm not getting any keepalives, so I'm just tearing down
00:12:11 - the session to that neighbor. So, with that being said, bunny
00:12:16 - is turned off. So we've got the tables themselves. Biggest thing
00:12:20 - to get used to, first off just like any routing protocol we've
00:12:22 - got our neighbor table. Great first step in troubleshooting is
00:12:26 - my neighbor there. But one of the weird things about BGP is this.
00:12:30 - You've got a BGP table and you've
00:12:34 - and a Routing table. I compared this a lot to the EIGRP topology
00:12:40 - table because it's kind of the same thing. BGP, let's say you've
00:12:43 - got a connection up here to ISP1, I'll just put I1 and I2, ISP1
00:12:50 - and ISP2. They're going to send you all the routes, BGP and I
00:12:54 - should emphasize, they're best routes. The ones that they're
00:12:56 - actually using that are in the routing table because they may
00:12:58 - have some uplinks to ISP three, four, five, six over here, they're
00:13:01 - going to send you everything. They're just going to get the best
00:13:03 - routes from each of those and then send you those. But that internet
00:13:06 - of itself, if that's an internet connection has a lot of routes. So
00:13:10 - you're getting the full internet routing table from ISP1 and
00:13:13 - ISP2. That's big. That's a lot of routes that are coming in there.
00:13:17 - All of those go into the BGP table. From there your router is
00:13:23 - going to go through that BGP metric. Remember those ten attributes,
00:13:26 - the way, the local preferences, down the list we go. This is
00:13:29 - going to pick the best of those routes and it has a lot of criteria
00:13:32 - like, you have to be able to reach the next hop and there's a
00:13:34 - lot of troubleshooting that comes into that but the best of those
00:13:38 - routes are going to be moved into the routing table by the BGP,
00:13:41 - well it's going to go through the BGP scanning process and move
00:13:44 - those into the routing table and then you are going to send the
00:13:46 - best of your routes. So you're going to pick the best ones and
00:13:50 - then send those to your neighbors via BGP. Let's say this is
00:13:53 - ISP9 over here. If you're a transit system you're going to pass
00:13:57 - those routes on and that neighbor is going to get the best from
00:14:01 - you and the list goes on and on. So you do a show IP BGP, you're
00:14:05 - going to see everything in this BGP table. It's a good place
00:14:09 - to start digging if routes aren't showing up in the routing table.
00:14:12 - Am I receiving them, are they showing up with little asterisk
00:14:14 - next to them, all of those kind of things. Now excuse me, you're
00:14:18 - going to be listed in the BGP table and then of course, we've
00:14:22 - got the routing table which is just like every routing protocol,
00:14:25 - list all the best routes that exist in your system.
00:14:29 - All right then. So let's take that and wrap all that up by looking
00:14:33 - at the key troubleshooting commands for BGP. First off, I know
00:14:38 - that you know that BGP is just for gadgets, it's a giant protocol
00:14:42 - so we could put a billion trouble shooting commands up there.
00:14:45 - I just want to give you the core that work most of the time.
00:14:49 - I would say, cover most issues. First off, show BGP summary.
00:14:54 - I would say that is by far my favorite command for BGP because
00:14:57 - it shows your neighbors which I know you're looking two commands
00:15:00 - below this and you're thinking, well that would show your neighbors.
00:15:04 - No, well it does, it does, but you're going to get like four
00:15:07 - pages of output for every single neighbor. It's going to be like,
00:15:09 - here's everything that I know about this neighbor. They're social
00:15:12 - security number, what lollipop flavor they like, everything.
00:15:14 - And it's very hard to weed through and get that information you
00:15:18 - want. This is like that good all show IP interface brief to where
00:15:21 - you're just like, "Give me the facts and give it to me quick."
00:15:24 - You're getting a table list of what every single neighbor, the
00:15:27 - big thing that you're looking for is what state is that neighbor
00:15:31 - in. So, I should pull up, I should pull out an output of this
00:15:35 - but you'll see when we see the troubleshooting thing. It's usually
00:15:38 - you'll see the IP address of the neighbor, their up time, blah,
00:15:41 - blah, blah. You're looking at the very very end of this command
00:15:44 - and it shows you the state. It'll either say, I think the title
00:15:48 - is like, it's the state and then slash and then puts like, prefix
00:15:52 - is received. If there is any words listed in here, that's a bad
00:15:56 - thing. If you see idle, if you see active, if you see any word
00:16:00 - that is listed there, that means the neighbor is not working
00:16:03 - right. You wanted to see a number here. You want to see like
00:16:06 - 500,000 maybe not that many but maybe like 200,000 which tells
00:16:10 - you how many prefixes or network advertisements you've received
00:16:14 - from that neighbor. So that's your first troubleshooting command.
00:16:18 - Do you see the neighbors listed there. It does the state show
00:16:21 - a number right there? If those two are good, then move on, do
00:16:25 - a show IP BGP. That's where you can see the entire BGP table
00:16:30 - that exists, so all of the prefixes that you're receiving, think
00:16:33 - of that as, like I said, your topology table, your link state
00:16:36 - database if you will, for BGP. But unbelievably,
00:16:40 - BGP is a distance-vector protocol and when you really know the
00:16:44 - difference between distance vector and link state, it's not so
00:16:46 - hard to believe. Distance vector again, its core attribute is
00:16:50 - that it only knows what neighbors are telling. Link state knows
00:16:53 - everything in the system and when you think about this scope
00:16:57 - and scale of the internet, good grief, I mean no way to run BGP
00:17:01 - if it were link state protocol because it have to know everything
00:17:04 - about everything. Whereas, distance-vector, this is far more
00:17:08 - reasonably, you only know what the neighbor has told you to know.
00:17:11 - It's just, again, when you our first introducing people to distance-vector
00:17:15 - and link state they're like, oh okay. So distance-vector is like
00:17:17 - this simple but like RIP routing protocol, I mean, that's why
00:17:20 - it gets in their mind and then when you say, well BGP is actually
00:17:23 - distance-vector like, oh, no way. That's amazing. So, anyway,
00:17:27 - we're fast. Show IP BGP neighbors, I talked to about that one
00:17:30 - already. If you really want to get nitty-gritty, you want to
00:17:33 - know everything about everything about that neighbor that's the
00:17:36 - command you use, so a lot of times, too overwhelming to be useful.
00:17:41 - And then you've got your two debug commands of depth. I say that
00:17:46 - because if you're not careful, if this is like an internet phasing
00:17:49 - router and you're receiving this from an ISP, for instance, if
00:17:52 - you're doing a debug IP BGP or an updates and you then cleared
00:17:57 - the neighbors, brace yourself. I mean, that's one of those could
00:18:01 - end the routers life kind of commands to where the router could
00:18:04 - lock up because you're getting hundreds of thousands of updates
00:18:07 - from a neighbor about different prefixes so, there's just going
00:18:10 - be a lot shown on the screen. So definitely, if you do use these
00:18:13 - commands to watch the communication, put some filters on it.
00:18:17 - Make sure that you're protecting yourself from getting too many
00:18:20 - updates from
00:18:24 - BGP. So that is BGP in a nutshell. If you're ready, I'm ready.
00:18:30 - Let's move into the troubleshooting. I hope this has been informative
00:18:32 - for you and I'd like to thank you for viewing.


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Jeremy Cioara

Jeremy Cioara

CBT Nuggets Trainer

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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