BGP Part 25 allowas in as override as prepend

allow is in love yes if this is one command when do we use this why do we need this let's assume this one is your private autonomous system 6 5 5 2 5 sounding it 6 5 5 2 3 no same number two autonomous systems your own site but in different location your own site in different location and these two sites are connected through public and ISP you know so you you did not purchase this private number it's free to use you want to use BGP to advertise your own network you know you will be having a layer 3 VPN tunnel through ISP only then this service is provided when you when you come to MPLS I'll be repeating these things again so you will understand where it fits in the real world advertising the private es to the public no one agrees but if you want to have in a your own tunnel between this then it is possible fight now you got your sights with same autonomous system and you want the communication and let's say we have 55 advertise from Road fight 44 44 44 44 advertise from rudra for the advertisement will go from retro fighter of the three and dr2 also will advertise it in router for but our before will not accept it why because when it when it receives 55 Network fifty-five network it will learn that it is coming from autonomous system 10 and 10 is received from six five five two five six five five two five is my own autonomous system the update says that this 50 Filatov originated from me then how should I accept it it's originating from me to prevent loop I don't think me I don't accept this BGP won't accept this to prevent loop when traffic is originated from its own autonomous system number to prevent loop it will not accept in this scenario I tell to harmful it's okay I love a it is like allowed locally yes that's the meaning of it allow a s in when you do that router for will see 55 network in BGP table like this when you say allow a s in here or if I will see 44 Network in BGP table now you can ping each other this is a lau AC do you have any question before we see the demonstration let's finish the other one the other one is is override company yes to overwrite is overwrite we can figure on router 2 you can figure it on all of the touch so when you say is override order to before advertising it to router for it will override with its ol number six five five to five will be overwritten or will be will be returned as ten seen stuff is in allow a scenic can use is override to solve each problem to solve the yes like if the traffic is originating from six five five to fight it will not accept because it's my own autonomous system so when you put a s overwrite the a s number of router five will be overwritten as 10 so when router for receives the update five five five fifty five fifty fifty-five will be seen like this ten ten to ten that's a is override both solves the problem so we need type show BGP and if you see if you see two times the same autonomous system two things are possible one they have used a so right or you don't have this duplicate a s number scenario let's say you'd just have six hundred and still you have two autonomous system for repeated which means to poison one of the route they are added they have repented some autonomous system number they have repeated some autonomous system number so that the a s path will be longer than the other part this is to poison the route this is to avoid the best route and pick the other looked Oh No so these are the things that I'm gonna demonstrate to you now if you have question you can ask now right now and wrote a five and four I'm going to remove EGP now hundreds of five no Beach no router bgp 30 and this is let's say this is going to be 65 and even this one is 65 - to do some sort of for all size River no router bgp I don't know what number to us Wendy Oh show at the BGP summary nice visibility all right let's put router bgp 65 - - to my neighbor is 10.24.0.2 remote is then that will be wondered what I see here is 44.4 folder for the folder for default mask to firefighter to fail to forget about this you know locks that is coming because the other side is still having the older configuration in order to show IP interface brief I don't have 44 Network so I'm saying interface a little bit 44 IP address I'm going to router 2 to do some alterations interphase g1 slash little I shut down for a while to avoid this log so undoubted 32 I am going to remove this one EP 10 now instead I'll put neighbor remote a yes then alright so I can't say no out now interphase g1 / 0 no sure I could be TV summary you see you got the new neighbour and you are learning one prefix from that neighbor which will be 44 Network see you're learning 40 furnace from me be sure I be G B you can see that it is coming from autonomous system 6 5 2 2 2 now let's go to low to 3 and do the alteration before we change Row 2 5 3 router bgp 10 do show run section now I'm going to remove this one and replace it with 65 - all right now in router 3 if you see show IP BGP you arse you're learning that 55 it's a valid next up address because undoubted to the next up self is given and it is coming from 6 5 2 2 2 now let's go to router 5 and have an interface called 55 with IP address for 555-5555 and then router bgp 6 5 5 32 neighbor cleaned out 30 4.0.3 remote AAS is dead and I'm advertising this network 55 but unfortunately this 55 which I'm advertising why I won't ask for to reach this 55 but are firmly not learning because the update is coming from the same number horrible system number likewise 44 I advertised not for expecting our five will will receive the update so that our if I can reach our for but show ibgp we are not learning 44 here let's try to debug debug IP BGP something updates updates and I want to refresh on our three near high PGP star soft all right see 44 44 44 / 32 is denied due to a s path contains our own ears look at this so nice can note the way that it can raise the issue straight stops very clearly straightforward and explains what the problems a spot contains its own yes so router 5 couldn't accept this right now let us type you all and then on our three if you check show ibgp you got 44 and the 5555 is coming from ebgp 44 is coming from ibgp which is relevantly but autonomous system is same for both so same thing will happen on our 4 also if you debug our 4 will also be filtering am I going to fresh it clear I PPTP star soft 55 okay here it is alright so how to solve this problem two weeks one is all right the other one allow a is in let me show another is in first thanks for doing that I want to say show IV bgp right now you are not learning 55 which is coming from other at all of us other other site your autonomous system same with our system number but in remote site router bgp 65 triple to the neighbor to allow AAS in that's it it's okay even if it is own autonomous system number you you can you can allow it that's the meaning of it so IP BGP now look at this even though it is it is your own autonomous system number you still learn it and the path is via autonomous system 10 you're still learning it that is internal fire you still you don't have the route because we have not 40 you cannot put the allow a sin so you don't have the Route 444 let's do that router bgp 65 triple through whenever you've learned that any sum any update from 35.0 dot three you can allow the a s even if it is your own yes you know if this is you know to avoid avoid look bgp will not allow but you are overriding that because you are very sure that loop will not occur you're very sure that you have your own autonomous system with same numbers in multiple sites now show IP BGP you can see it ping source boom right you're pinging between to make to in networks that are in different sides would seem autonomous system all right I'm going to remove this I love you scene and put a override we are like a GPS so I've gone 44 and then now we are going to say router bgp 65 okay so uh no trick to what I'm going to do this okay before that let me let me show you the output there is no fifty-five here schweppe enough to fake God so we cannot pin now I'm going to do and say router bgp ten whenever you speak to the neighbor 10.24.0.2 is over right use the roadmap so I'm going to say it can be for specific Network like 5555 for any network so I'd say access list 10 permit any roadmap roadmap just yes for right I'm just putting a scene match IP address access list number 10 set okay but this is one more thing I want to show you a spot but we will see that less next one it should be here only a so right comment in this version of our printing system I don't have but if it is a service provider one H service product sexual coercion it's an advanced an IP service pet but I don't know why hey the command is not available so that's the syntax when you put that what will happen is routed to will advertise by replacing six five two two two it puts number ten so in router for receives it entry to see fifty five fifty five fifty by 10 again another ten it will not be six five two two two you know it's better to use a so allow a s in because you know the solution you are achieving easily even though you don't have a command is alright but if you have a so right you can see the provider has got A's overnight they can override and send it to you but you need to depend on the provider for that whereas Allah s in you have a solution on your own in your hands by your own you can do that alright so yes override hope you can manage when you have a situation in your production so that if you are in an ISP level if the customer is requesting you to do this like we have multiple sites with the same autonomous system allow the traffic to past or something like that then you know the solution what to do as a service provider you need to put the command a so right if it is not service provider then you have to do by putting a low AC now what poor thing that I want to show you here is one more thing that I want to show you here is you can poison a root by adding some s numbers in the pot now let us now use the allow a s let's now allow the a s in an hour for I'm saying a router bgp 65 and also in total five I'm saying hello AC now you will get the route show IP route you got this route 44 so I believe God now assume now this is not the right topology to explain that but I'm just explaining the since you have seen big big topologies paper you can visualize what I am saying or let me show you with this picture but my demo will be different I'll use this picture you see to go to the 66 Network this was also partially release scenario which he gave me study the 66 Network will be by default going this way both 66 and 166 and 77 network will be going this way because of the less AAS jumper I want to use a s path attribute to put 66 in this path I want to put a 66 in this path by using a century his path intended not local for friends or wait is path attribute I want to do this and this one you can do it from anywhere you can do from before you can do from means you can do from the neighbor autonomous system you can do it from your own autonomous system it can be done on router for our router to or even it can be done from row to row six if a router six don't want someone to come through this way for sixty six to need to take the other path like this anyone can do this adding a s path we can add yes but actually it is coming from sixty when this guy receives order to receives it will say 66 66 66 66 I are receiving from six five two two two and that is coming from sixty this is how it should shop actually only to hop but to poison this route to make it bad route you can add some values like two times sixty six three times 66 so that the hop count will look bigger this way and this way it is one to just three three hops so you can add more autonomous systems repeatedly to increase the hop count that's just what the point I'm trying to explain this is what I'm going to demonstrate how to add the hops for that you see I'm going to show you that I'm going to row two three and right now router three when I receive 55 Network I'm seeing this one hop router no before the less right a roadmap with a seal access list 10 permit host 55 then route map this is just far enough yes but no need to put all the same attribute me part increase insertion then match IP access lists match IP address then if this match happens set a s path C prepend command prepend the ace number are the last years has something else lastly is nobody can I prevent last year's juice the different is number this is also one way to allow the traffic you for the prima scenario but not widely in use so I'm saying repent is number 10 again 10 or you can also put different number let's use the same number which is there the topology I do this now router bgp whenever you learn any update from 10.35 dot 0.5 use the route map wrote Nam name I hear is yes but in one more thing I need to do is I need to use the route map I need to write the route map 20 sequence novel for the other traffic's just just follow the snow show ibgp clear let's go to dr. foreign cheek no it's not happening so I should not use ten I should use different numbers two or three ha look at this it's happening he took some time you know it will poison the root it increases the Hopkin right so it is it took some time now let's go to Raja for yeah more hops now this is also used by some people and they want to choose one path and take the other but so now this is having too many hops if there will be another path to reach 55 and long path this is not a genuine person in part this was a genuine path with less up come but now we have poisoned it so it will take the other path with her which has got the less hop which might have not been a default based path before right now when this part when that path ghosts are automatically fall to this but this is by using a s path attribute you are tuning the beaten path me to be part traffic engineering using yes right now it's your time do you have any question we have seen and now is in ace all right yes Pat prepend and any other question you have based on your demo lab that you have practiced you can ask them all right if no do some work on this weekends

Channel: Jayachandran

Views: 354

Keywords: ccna, ccnp, ccie, subnetting, networking, jayachandran, sathiyan, training, online, switching, stp, security, BGP

Id: TRIvIXeQUQQ

Length: 33min 33sec (2013 seconds)

Published: Fri Jun 12 2020