Using Nexthopself - Video By Sikandar Shaik || Dual CCIE (RS/SP) # 35012

[Music] in this video we'll try to understand the default BGP like stop behavior the next stop is one of the attribute which can be used in the best path calculations and it is it is well known and manager attribute so whenever a BGP carries its routes it is going to carry the net next hop information but the behavior of the next stop is slightly different when compared with our normal routing protocol like here I got some points view BGP is an ASIS protocol not as routers by router protocol so which means BGP will only changes a next stop when it changes the autonomous system number ok let us try to understand the difference here I got a very simple diagram here you can see I got autonomous system 500 here 600 and I got from four routers in that and I just named those routers as BC a b c d e f g some names it can be any IP address I am NOT listing any specific IP just to make it very simple I'm going to name them with some respective alphabets now what I want is I am just trying to understand the default routing behavior and and the default bzv behavior so we'll try to compare and then we will try to understand what is the default next or behavior in the BGP so take an example I got a router 10 dot Network now I want to make sure that tails general network whenever BGP inside the bgp router day is going to advertise to router B because it's an external bgp neighbor and then the outer b is going to orders to see as well as it is going to attach to d as well as it is going to advertise to e now depending upon how you configure your ibgp neighbors ship here because if you're using full mesh we will send to everyone if you are using router factors then it will send to RL server and from there it will go but anyway the update will go to all the neighbors and from the router e again it will go to F and F is going to forward to see now where it is forwarding it is also going to carry the next top information like the B network will be anyway it will be addressed along with the next top information because BGP also carries the next stop information so if you talk about normal routing normal routing what we learn so this is our normal routing so after a 10 10 dot network will be advertised by router a router B now router is going toward a out of B when it is analyzing 10 dot Network what will be the next shopper next reporters will be out right because the router beer is used some router a so which means the next or bottles will be these circles whatever the IP arrows now B is going to forward it to the out of C now C is going to receive the same network but what is the next hop address the next row of purchase will be generally it will be B and C will forward to D let's say if you're in case of normal routing next up is maybe C and then extrovert is maybe e sorry T so in case if it is going to route or D or E or else if d router is directly sending to e because of full mesh but all the routers and extra orders will be e only right or it can be C or it can be T so I am just taking as a normal routing so in case of normal routing if you remove the BGP concave beach be part the next reporters will be B here and on the router D the next reporters will be C and on the router a the next orders will be D because D E is going to this user out from D which means the next reporters it's going to write as T from there the update goes to F F will rise the next operators as E and G is going to write the next reporters as f because next stop simply next starter all right that is what we learn in our normal routing configurations if I use any of the routing protocol like OSPF EIGRP our IP any protocol the next operators will be always the next router uh truth there is something called normal routing so we are talking about normal routing what we learn so now we'll try to understand the behavior of the BGP now now we are going to verify with BGP behavior now in case of BGP behavior how the next of the behavior will be now when the router B receives the next job butters will be a now when the router series use the next operators will be again a again it will be a it will be a now again after that now the next hop address will be e and the next orders will be so now you may now we need to understand what is this exactly now in case of BGP there is a rule that whenever any update is send one ibgp neighbors sending any update to another ibgp neighbor which means when the update is going within the same autonomous system nimble between the same ibgp neighbors ships the next hop address will not change the next hop address remains the same so and in many update it is sending some money which be neighbor to another ebgp neighbor which means when it is going outside there is it is going to change an extra behavior so which means in case of BGP the default behavior of the next storm is when it changes the autonomous system number then only it is going to change the next orbital but when it is added izing to the same routers if it's in the same autonomous system number it will not change the next hop so that is something what we need to understand with this scenario here so let me show you again here now in my diagram my diagram here the next job orders now this is route is coming from external bgp neighbor so when a route is coming from external bgp neighbors it is going to write this as next hop that is again same in both the cases normal routing as well as BGP routing but when in any update and B is sending an update to see where it is sending to B where it is sending to E which means whenever it is arising the update within the same a is it is going to or dies attend all networks at the same time it will not change the next opera because when it is when BGP is going to arise any network it will also include the next stop information but when it is analyzing to the same autonomous system numbers or the routers it in the same is it is not going to change an extra which means that n dot network will be allowed to router C with the same next top a and then say next top a same next from a and then when the same updates the same technology work is allowed to another ebgp neighbor now it is going to e be GT neighbor now when F receives S will receive an extra paddles to the next round runners which means now here it changes but when the router F sends to G again it is not going to change the next all now there is something the default behavior in BGP BGP will only change an extra when it changes the autonomous system number now B is going to receive the update and it is going to forward the suite the same next job to all the routers inside this now this might affect your network reachability song in some cases because let's take an example I got the same diagram here also now let us take an example this is our niche Network gains let's say 15 dot one dot one dot one this IP address of this network now router C is going to receive the network with $10 at work and the next job or this is a something but 15 dot one dot one dot one now if the router C do not know how to reach the next job then it might affect your reach ability so you you will receive the route but you don't have the best route and you will not be able to communicate with the $10 at work which is no different is so now there are two possible solutions either you can to fix this type of issues one option is either you need to advertise all your the value interface so the first solution is advertised all your van interfaces which is very less because advertising the line interfaces again makes your means you need to authorize all these van interfaces inside the BGP so that router C should know where is that 15 1 1 1 so that it can forward the packet directly to that address or what I can do is the best option is to change this next stop behavior now we can manually change the next top so to manually change the next stop we need to go to the border routers here I need to go to outer B and inside the router bgp 500 or 600 we need to go to router bgp 600 and then i had to say in abel whatever the neighbor neighbor in my example it is C so it can be IP address actually neighbors see I am going to say next of self-command so when I give this command automatically it am saying that whatever the updates I am sending to this neighbor please change an extra bar just Amaya's so by default the next hop address will be a now it will change to B now similarly you can do the same thing for all the internal labels neighbors pointing to D and then I am going to say next top self-similar I can say label pointing to e next offset so when you ne apply this command on the bottle outer pointing to our internal routers so we are manually changing the next top behavior to these things that's the reason we we use an extra press command select ops command is really required if you want to change the default next or behavior and the default next stop behavior is by default within there is the next stop will not change so what I can do I can say next top serve on this router so the next top orders will become B on this router now even if the next table others is be the probably ear outer knows how to reach B because internally we are also running IGP and in that IGP we are organizing those networks maybe I always PF am running I am just terrorizing my networks inside the wispy of non outer iNOS wait is b so automatically it will not affect your reach ability so it's something we need to keep in mind if you see that out in the routing table so now if the next table is not reachable you will not see that out in routing table but you'll definitely see that out in the beach in the BGP table so definitely it will affect your reach ability there are two possible solutions either your dies the vine interfaces or change the default next or behavior by using a command called next stop cells something what is recommended now similar way if you are if you are doing from the other end let's take out a few feet of network here now you are seeing that out from G to F and from F to E you are getting the route and router II will send to D without change the next stop but I can go to the outer e and I can say neighbor D next stop cells I can do that but similar I can do the same thing on the other end also so this is the default behavior of the next stop so it's really important to understand now we'll try to verify the same thing by a lab now if you remember in our previous video we have done a very basic ebgp configuration as for this diagram so I am going to continue with that and I already did this ebgp configurations now I am going to verify the D for next stop behavior so let's go to my console screen here so I got my diagram here this is my screen here and if you verify in our previous video we did these basic ebgp configurations with the outer one is already establishing neighbor ship with router 2 and advertising the val interfaces now anyway I am analyzing the Valley interfaces here so I think it won't be infect the reach ability but we want to verify the default next-hop behavior here and if you verify my router 2 BGP configurations now router 2 is already contrary its neighbor one dot one dot one dot one in 500 and neighbor 3.2.2 dot 0 2 in 600 and on the router 3 this is pre-configured so if you want again continue with the same lab what you did over there or as you can start from the scratch and make sure that you finish this configuration so now if I verify on my router 2 I can see both of my neighbors and from both the neighbors I am receiving around so now we will verify the next stop behavior now I will say show IP BGP or if I say show IP route BGP if you try to see you the next hop address for studied or network is 2.2 dot 2.2 on the router 1 now by default so here I got a very simple scenario here so this study door network is a - - router or two and then I'll totally use this study tour network and the default next hop address will be what is the next Roberta's to door to door to door - because it is received from this neighbor 2.2 door to door - that is my router 3 connected interface now what's happening here is router to is are sending update to internal BGP neighbor the same network but without changing the next hop and the next hop address is - door 2.02 only without saying the next stop so that is something what's happening here now if you try to very far here or you can you show IV BGP BGP table here also you can see that even at work I am getting and the next hop address is 2.2 da - da - on the router one that's my next one or you can verify with this command more in detail you can see the next reverses is 2.2 dot dot - okay it's coming from Wanda Wanda one or two okay so anyway this BGP tables those things are getting to more in details and I when I get into my path manipulations process now in this case I really don't have any problem communicating with 30 dot one dot one dot one I can still able to access because I advertise the one interface if you remember now router1 if I verify my routing table where outer one to reach this network it has to go y a2 dot 2.0 - and it knows varies the two door network it is on this yr 1.1.1 or two so now in this case I don't have any problem in communication because I did the rudiments of Van interfaces here let's say if I don't do that so what I will do is I will try to go my put my router three and I will remove that to door network from my advertisements the same thing I am going to do on the router - as well on the router - I'm going to remove that two door network from the advertisements now if a very fine you can see the student network is not present now even if you are very far here the sides or network the next top artists is this and if a verify my routing table there is no tile or network because there's a 3G cellular network the next hop address is 2.2 row 2.2 and router one don't know where is 2.8 or 2 because of this default next stop behavior now analyzing all the wire interfaces is really not possible so either you can go with that option but what I want to do is I want to change this next sub behavior to a normal routing behavior so I will go to my router 2 and then I will go to my router 2 and Elson neighbor what's my neighbor neighbor is 1.1 1.1 and I'm going to say next stop self-command there's something I am going to do so I'll go to my router 2 and then I will say router bgp 500 and ponding to my internal labels so majorly done on the border routers pointing to my internal routers and then I will say next top self-command done so once I do this now if a very fine my router 1 show IP b GP or if i qi p bgp so previously you can see the next two bottles for this before i configure the next top self-command now if you verify the next hop address automatically changes to router 2 because I have ID'd that manually by saying the next stops of command so now if a very fine my outing table show IP route BGP you can see this cellular network router has so you can see that out in my routing table and if I try to ping I should be able to ping so this is something very useful this is a very basic lab for understanding the next wrong behavior when you are working with a big-sized networks definitely you need to consider these things so whenever you are receiving any routes from XL BGP neighbor and then you are arising the same routes to internal BGP enables make sure that your next opportunity in case if the next or process is not reachable or this one interface in order dies so make sure that you change the next hop address to your a local router address it in the same is by using the next tops of commands [Music]

Channel: Sikandar Shaik

Views: 55,215

Keywords: bgp, bgp videos, noa, noa vdieos, ccna, ccna videos, ccnp, noa videos, cisco, ccie, subnetting, ccna security, ospf, firewall, ccna subnetting, ipv6, stp, ccna vdieos, ccna free video, ccie certification, ios, iou, virtual, eigrp, cisco virtual lab, iosv, asav, gns3, routing, noa solutions, zone based firewall, zone pair, zbf, flsm, cisco firewall, cisco security, cisco certifications, wan, ip addressing, netmetric, vlsm, eigrp configuration, vlan, ccna, ccna videos, ccnp, noa videos, cisco

Id: vJXYjfy_O8s

Length: 17min 48sec (1068 seconds)

Published: Mon Mar 06 2017