BGP Split Horizon and Route Reflector Client

hi everyone my name is Sandeep welcome back to another session of PGP let's start for today's session okay so today we are going to teach bgp split horizontal and how to overcome this so there are two solutions route route reflected client and which be full mesh so before we start let's understand our topology let me take a screenshot of this okay so what BGP split horizontal says that if you have an eye bgp neighbor between two routers the route learned from one IP GP neighbor will not be sent to the next ibgp neighbor let me explain it more let's say I have this 200.000 network which is learnt on router 1 ok and this node is being sent from router 1 to router 2 so this route has come here onto router 2 200 0 0 1 this route will not be sent to the next ibgp neighbor so this route 200.000 will not be sent to router 3 ok this is a BGP split horizontal this is used to avoid the routing loops and by default BGP is gonna block this route from advertising from router to router 3 ok so we are going to do the practicals and we are going to see how it is going to work so to give you a brief we have three routers router one router 2 and router 3 all these three routers are in BGP autonomous system 100 and we are going to advertise this route 200 G row 0 1 ok so let's go ahead and start doing the configuration we will understand how the routes are not getting propagated from router to to router 3 we will verify the BGP routing table on router 3 and then we will go towards the solutions that is route reflector and full machine ok let's jump ahead on to router 1 this is my router 1 I'm going to quickly configure the IP adresses see the interface FA 0 slash 0 IP address 10 dot one dot dot one two five five two five five and I'm going to execute no shirt on this that's it so let's jump on router to term interface FA 0 slash 0 IP address 10.1.1.10 - 2 v 5.0 no shut interface FA 0 / 1 I P address 10.1 dot t 3.2 - 5 5 this let's verify the connectivity between router - and router 1 first pings 10.1.1.1 I should say a ping is taking some time to learn the app let's jump ahead on router through three interface f8 0/1 I peer res 10 dot one dot twenty-three dot three to five 5.0 no let's say just do a ping n dot one dot twenty-three dot two to the router to looks good okay so right so let's start doing our BGP configurations now so far what we have done is we have these IP addresses configured here 12.1 and 12.1 we have this up and working okay so let's go ahead and configure this IP address on one of the loopback interface of router one and we will bring up the bgp between router one and router to also between router two and outer three so let's go ahead and do the BGP configurations first on router 1 and router 2 okay let's see hundred neighbor ten dot one dot dot two autonomous system is 100 let's go ahead and do the same configurations Rueter bgp hundred neighbor 10.1.1.1 remote autonomous system is 100 and we should see a BGP coming up shortly here let me bring the second neighbor 10.1.1.1 over system is 100 and we will go ahead and configure router bgp 100 neighbor ten dot one dot dot remote autonomous system is hundred let's wait for for a minute for BGP to come up show IP BGP summary it shows state is active it's still an active state let's do a quick ping test to make sure that we have reach ability Bishop is going to take 180 seconds okay so we could say that the BGP is up here bgp neighbor shows up so let me quickly verify show IP BGP summary here you could see the we have neighbor ship with 10.1.1.1 OMA system is 200 messages received and message is sent and you could see that this is up since 12 seconds and we have received zero prefix which means that if I execute show IP BGP I don't have any prefixes learnt here similarly let's jump on to router 2 and verify that we have two neighbors show IP BGP summary we have two neighbors okay so what we have done is on this router I have performed an eye BGP between router 1 and also on between the router 3 so I am going out a 2 and you could see that I have to be cheap innovation ok so I am on a router 2 here and I have bgp neighbor with 10.1.1.1 which is this IP address and the next neighbor is with with 10 dot one dot dot 3 which is this hydration ok so far we will we are good with the configurations so what we are going going to do is we are going to add a loopback IP address with this IP address 200 0 0 1 and I am going to advertise this route into the router 1 okay so this route should come to router 2 but this should not be advertised to router 3 alright so let's go ahead and configure a loopback interface loopback 200 I'll give I pay address 200 dot zero dot one two five five two five five zero and let me advertise this route into bgp so to advertise this route I'm going to use a network command to hundred zero zero zero mass will be 255 255 255 dot zero so now I'm advertising this route into the BGP show IP a quick verification from router one to see that we are advertising this show IP BGP neighbor 10 dot one dot dot to advertised routes ok so we could see that this 200 network is being advertised from router one this is the best path this star indicates that this is the valid path and greater symbol test that it is the best best best route okay so this is being advertised from router one let's quickly understand this so this network we have created here two zero zero one and we we are advertising this route into the BGP so let's verify on the router - if we have learnt this route so I pp GP summary you could see that one route or one prefix is received from 10.1 or 12.1 ok so if you go ahead and check that show IP BGP you could see that its best route it's valid and best route 200-300 I am learning from 10.1.1.1 so far this looks good sure IP route so I figure out you could see that the route is learned from BGP here the same route should be advertised to the router 3 as it is in its routing table however it is not going to do that because of BGP split horizontal which tells that the route will not be you don't drop two three okay so let's just quickly verify so IP BGP summary you could see that we have received zero routes show IP BGP you don't see any route do show IP route you don't see any route here this is the BGP split horizont to avoid any routing loops okay so so far we are good with this so we sent a route from here 200 it is learnt on this but this route is never getting advertised to the next router okay so to to fix this problem we have two solutions first thing is that we could configure this router to as a route reflector client route reflector client there is one command you need to execute neighbor 10.1.1.10 flector client and also you need to execute neighbor 10.1 or twelve dot one route reflector client which means that this route learnt here will be propagated to router three so let's verify that let me see if we could log the messages debug BGP Ambridge debug IP BGP updates IP BGP you wench let's see if we could capture the route which is I learned on router 3 okay so let's verify quickly what our configurations look like you're running section BGP okay so the configurations are pretty straightforward let me go ahead and configure route reflected client router bgp 100 vp hundred the command is very simple its neighbor ten dot 1.3 dot three route reflector client that's it please note that when you configure a router reflector client in a production network your bgp neighbor is gonna flap so you could see that the BGP neighbor has terminated and it has come back up so this will be disruptive change so if you are in a production please make sure that you have all the downtime and things like that ok so I am on so I am on this router now and we could see that debugging messages are logged in here right so let's see what's happening okay here okay so when we configured this route reflected client okay let me stop the messages okay when we configured the router afflicted lined the BGP neighbor got reset BGP 10.1 or 23.2 reset due to peer close decision when we configured it out reflected client the router to close this TCP session we of BGP and it has come back again as soon as it has come back again you could see that we see you know we received an update from router 2 okay and then we could also notice that we have received this route 200 euros ero / 24 now which earlier was not received but you know there is one more problem in this network that you could still see that this is not a valid path it also tells that this is still not a valid path 200 zero zero zero is still not a valid path so let's quickly verify show IP BGP summary first to make sure that we are receiving that 200 Network so we have received this 200 Network if I execute show IP BGP you could see that this network is learnt 200 0 0 0 and you could also see that this is internal I indicates that internal it's a valid but what we are missing is this is greater symbol this is still not a best route okay so can you think of what would be the problem here is any idea in my previous classes we discussed about bgp synchronization which means that when you have a BGP okay the rule of synchronization says that any BGP routes I bgp route you know if you learn any any routes from the third party it will need to be and when you are advertising it to the next router it it needs to have an it needs to learn through IGP so you should have the interior gateway protocol it could be your OSPF or eid RP or any other routing so what we are going to do here is that I'm going to use ICP configurations here okay so we were discussing that the 200 Network is learnt however it is still not the best path right so what we are gonna do is that let's quickly verify show IP bgp 200 zero zeros you know you could see that the next up is 10.1.1.1 which is not accessible so you should have a ICP running in the network and you should have reach ability to 10.1 or 12.1 so what we will do is let's configure any IP protocol foreign for instance let's configure router GI g RP or Rooter OSPF one and neighbor 10.0.0.0 or let's say let me realize all the networks okay sorry it was my typo instead of neighbor we should use Network Auto summary show running section OSPF let's do the same configuration on the other three routers quickly okay now I should have the BGP route here instead of inaccessible it should come as reachable let's see why are we still not having negotiable okay the OSPF was still conversing and I could see that it's loading and then it has converged to full state now so I should see this route here which means that we should have this route as accessible and that's it you could see that this is the best part now when available route and it's the best part and it is reachable so this is the BGP split horizontal you could see that in before we configure the route reflector the route was not learned from BGP ibgp neighbor and as soon as we configure this is a route reflector client you could see that the route is learnt ok so what we will do is now let's remove the eye BGP route reflector client configuration the first solution which we applied we will remove that so running section bgp router bgp hundred and i'm going to remove this command you could see that as soon as you remove this the BGP neighbor ship is gonna flap and let me verify this again you could see that show IP BGP neighbor and the route is not learnt in the BGP because of rule of you know BGP split horizontal okay so they're now the same scenario again we are back to square one the router one has advertised this route into ibgp the router 2 has learnt this but router t2 is not sending this route to the third neighbor so we had seen the first solution that is BGP route reflector now we will see the second solution that is BGP full mesh let's quickly verify show IP BGP 200 0 0 0 is learnt here ok so you could see that this route is here now BGP full mesh means you should have neighbors ship from each and every router so the same topology I am going to draw this way router to this is router 2 and you have router 1 and this is router 3 we have these ibgp neighbors this way and now we need to have one more ibgp neighbor to make this as a full mesh as soon as we establish this neighbor ship between router 1 and router 3 then this route will be propagated ok so let's go ahead and do this from router 1 so from router 1 I should have a reach ability to router 3 so the router threes IP address is 10 123 3 and 10 dot one dot 12.1 okay so alright let's go ahead and do this rotor bgp 100 neighbor 10.1.1.1 homage system is 100 router 3 let me just jump on to the router 3 Rooter bgp 100 neighbor 10.1.1.1 remote autonomous system valid okay and now you can verify that the bgp neighbor has come up 10.1.1.1 now on this router show IP bgp 200 0 0 0 and i should have this route here ok so far we have seen the two possible solutions for the BGP split horizon truehl ok the first solution we saw is route reflected client and the second one is beautiful mesh thanks for watching this video and I hope this has been informative if you liked this video click on like button and subscribe my channel to get the more videos regarding BGP and all other technologies thanks a lot have a good day

Channel: Sandeep S

Views: 305

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Id: Alxq83jdj3M

Length: 24min 2sec (1442 seconds)

Published: Tue Oct 23 2018