Cisco CCNP ENARSI - BGP Configuration

[Music] hi this is David Voss CCIE 1 1 3 7 2 and in this video we're going to be going over bgp configuration so here's specifically what you're going to learn you learn how to enable BGP on a router and then also how to bring up bgp neighbor relationships then you're going to learn about advertising networks to those neighbors and then taking a look at the BGP table itself as well as some best practices on implementing BGP in your environment or simply to be able to answer the appropriate test questions so there's certain requirements that you need to know about when you enable BGP and that is you need an autonomous system number you type in router bgp in that autonomous system number that normally is a number that has given you or assigned to you and then you need to know the IP address of each and every neighbor that you would like to communicate with you would type a neighbor there the IP address of the neighbor and whatever there the remote is so you need to enter in whatever their remote a s is that's it that's required so here we see for example router bgp 1 our neighbor is 10.1.1.10 neighbors other certain requirements Ras must match our neighbors a us as they point to us so when they say I need to communicate with this neighbor they need to make sure they get the a s right the bgp router IDs are the two routers must not be the same if there's configuration obviously that needs to be configured correctly and then each router must establish a TCP connection with its neighbors note the remote router IP address must match what the local router configures in a bgp neighbor remote a s command so instead of talking about this because that could get confusing let's actually do it let's jump into the lab and we'll be working on the point-to-point between rudder - and router 4 so here we want to enable BGP on router 4 and we simply do that by typing router bgp and let's say our autonomous system number is 10 now we want to establish a neighbor relationship with router 2 - their serial interface so then we type in neighbor the IP address of our neighbor and then the remote a s and we'll say they're remote a s is 10 as well so this is an AI BGP connection which we will talk about later but basically we're connecting two routers in the same a s and there you see our neighbor is not up we see it in our BGP table but it's not up and active because we have not enabled it on router 2 so on router 2 we type router bgp 10 the neighbor the IP address for root router 4 and now we should see this neighbor relationship come up and it may take a second here there we go so now then the BGP neighbor relationship has come up between router 2 and router 4 simply by entering two commands on each router we now have a valid bgp configuration now when I show IP BGP which shows the BGP table or show IP route we don't see any BGP routes being shared because we're not inserting anything the BGP just yet so how do you advertise networks you can do it many ways you can do it through propagation of received BGP routes that you're already receiving from someone else you can redistribute routes into BGP you can source the routes from your actual router and you can do that by using the network command which would specify the exact network you would like to insert into BGP and there needs to be a match for that in the local routing table or you can use the aggregate address command which does what it says it a grits multiple routes into one larger route so here's an example of the network command router bgp autonomous system and then the network 191 6 8 1.0 / 24 we want to advertise that route and that would do it now what is the BGP table at a high level the BGP table contains all learned BGP prefixes so it takes all the learned learned prefixes from all neighbors and then from there it chooses the best path from those options and that is the route that it advertises to its neighbors so let's take a look at some of these concepts we're on router for now and let's say we have got a route here that we were learning 10.10 dot but we want to advertise that in the BGP and we do that via the network command so you can see 10.10 dot into BGP that route we've learned via eigrp is now going to be advertised via BGP from router for over to rudder - and we show IP bgp neighbor the route the neighbor IP address in the advertised route and you can see that we are advertising this route in router 2 will certainly show that they are receiving this route now on router 4 let's go ahead and redistribute connected routes there's another way we can advertise routes so let's go ahead and take a look at the routes we are now advertising over to router 2 and now you can see we are also now advertising connected routes so those are just two ways you can advertise routes from a router via BGP and as you can see router 2 is now receiving all of those routes in on rudder - swatting table you can see the BGP route marked by a B is now in the routing table all the BGP routes are marked by the letter B so let's go ahead and do a quick review of ebgp versus i bgp now let's say we have an autonomous system 200 and we own four routers and we connect them all via BGP being that they're all in the same autonomous system we need a full mesh that's a rule within ibgp and these are again all ibgp connections because they're all connecting to the same autonomous system but let's say we have two different providers Internet service providers one is a s 301 the other is a s 450 these connections are each ebgp connections because we are connecting two autonomous systems that are not our own so an a s 200 we have full administrative control that's ibgp between them and then ebgp connections to our upstream providers where we do not have a ministry of control now let's take this concept and actually implement it in a lab so router 3 and router for what we're going to work on now now remember we have an AI bgp connection already between router 4 and router 2 so now what we want to do is we're going to create an e bgp connection to router 3 so we're gonna we're gonna do a neighbor statement over to router threes interface serial interface and that remote a s is going to be 999 that's going to be our ebgp session over to router 3 we're treating them like for example an internet service provider and now on router 3 they need to do the same otherwise the neighbor ships not going to come up so they do router bgp 999 they point back to us on the other side of the link and they put in our remote a s and they create their EBT P programming and then this neighbor relationship will come up and the neighbor relationship has come up between router 3 and router 4 and now you see on router for we have an eye bgp session 2 router 2 and an e bgp session 2 router 3 s 10 and a s 999 respectively pretty straightforward concept but now you know so a few best practices in rolling out bgp you should use a loopback address for neighbor ships we've not been doing that yet we've been using interfaces and when you use loop backs you should manually set the router ID and then you should also use ebgp multi-hop an update source loopback bgp by default will not communicate to loopback addresses you need to allow for multi-hop communications time to live with bgp is usually 1 you need to increase it to higher than that so I want to talk about some of these concepts so let's go ahead and do let's go ahead and enable bgp in a typical way that you would do it on router 3 we're going to start from scratch here again and enable bgp on router 3 and we're going to use loopback 99 on both router 3 in router for to set up our bgp neighbor session while loop x lube x are stable they don't flap they can be learned via multiple interfaces interfaces flap but loop backs do not so ideally you're gonna want to establish bgp between loopback addresses so and so we have the loopback addresses with IP addresses then you also need to make sure you have an a static route in place to make sure that you can reach the loopback on the other router since we're not advertising it via nigp we're just gonna use static routes for that and then we type in router bgp 10 we're gonna manually set the bgp router ID to the loopback address 10.30 dot 30.1 and then our neighbor is going to be the loopback of router for 10.40 dot 40.1 and then we are gonna set a bgp multi-hop to increase the time to live from one and let's increase it to 3 if it stays at one this neighbor ship would never come up we need to increase a bgp multi-hop to 3 so the loop X can communicate and then we're going to make our update source loopback 99 so all of these are really required or properly roll out bgp between loop backs and we'll do the same thing on router 4 and we will soon see this neighbor relationship come up and there we see that the neighbor relationship has now come up between the loop backs so we have a valid and stable Rene be relationship between router 3 and router for now let's go ahead and redistribute connected on router 3 and make sure that router 4 can actually see those routes and we'll look at the BGP table we don't see them yet often clearing BGP clear IP BGP star soft is something that will reset the neighbor relationship and will allow for any changes you make to be implemented and in that case we now see that we've received the routes from router 3 finally let's just do a quick review on BGP attributes so let's say we have a web server and we are hosting it within our autonomous system we have three routers connected via a BGP and then we're connected to two different service providers using ebgp and let's say we have users on the internet who are trying to get to our web server and they see this is pretty much an often equal equal distance so half of our traffic's coming over one link half of our traffic's coming over the other link there both we know where as50 and the way the users see it right now is that we're just a couple guesses away so we want to make one path preferred let's say there's one circuit that we want to use more often than the other we can add our a s over and over again and prepend it to what we advertised out to our provider let's say on the top here and then the provider on the top would see these multiple and implement these multiple AAS additions to the attribute of the routes we send them users would no longer prefer that path they would prefer the the other path that had just won a s listed but if that router went down and then the users would choose the less preferred path now that's a that's a high-level example of how you can manipulate a s path but let's do it let's do a route map a s path and then and then we're on router 3 here by the way and what we want to do is we're gonna say in this route map we're just going to set the a s path and we're going to prepend is the proper word we're going to prepend and we're going to keep adding ras over and over again and we're going to prepend it to our advertisements out to router 4 and then router 4 as you can see right now the path is just one instance of an AAS well we're going to change that with this prepending we're going to apply this route map to our neighbor relationship to router 4 and we're gonna place it outbound so any outbound advertisement we give router 4 will have a prepend of these AAS numbers we're gonna clear the bgp session and then now look at router for all of these additional a s numbers which makes the path less preferred that's just one of many ways you can manipulate bgp attributes to affect routing so here's what you've learned you've learned basic bgp configuration you've learned how to enable it and turn up neighbor ships in bgp you've learned how to advertise networks in bgp and how to take a look at the BGP table at a high level you've learned best practices with BGP using loop backs and then you've also looked at the BGP attributes and how to manipulate those as well good luck in your studies

Channel: Paul Browning

Views: 804

Keywords: cisco ccnp enarsi, BGP configuration, Routing Fundamentals, Layer 3 Routing OSPF, EIGRP, OSPF, OSPF Concepts, border gateway protocol, BGP Concepts, IPv6 Addressing and Migration, Troubleshoot IP Routing, VPN Technologies, RADIUS and TACACS+, Network Troubleshooting, Troubleshooting Methodologies, ccnp enarsi exam, bgp cisco, cisco bgp configuration, bgp configuration example, cisco bgp configuration example, bgp configuration step by step, configuring bgp on cisco routers

Id: yLQFuOYe5Gw

Length: 16min 43sec (1003 seconds)

Published: Wed Apr 29 2020