BGP Path Attribute

hello and welcome to this short video of BGP path attribute my name is Ahn run in the short video we are going to learn about be GPS attributes be gp's metrics are called as attributes BGP path attributes for understanding BGP attributes we have taken 7 routers and they are in different autonomous system we have around five autonomous system here on eternal bond router on router 5 router 4 6 and 7 BGP is already configured and r2 is also configured as in the EB GB now I'm going to configure a BGP on r3 so I will say router bgp 10 neighbor 35.0 0.5 remote autonomous system is 21 more neighbor i have in autonomous system 10 that is 13.0 done 0.1 Ramudu s is thin right similarly I will go to r1 and say router bgp 10 neighborís 13 dot 0 dot 0 dot three remote autonomous system is 20 I'm sorry it is not 20 dis same autonomous system status 10 neighbor to l dot 0 dot 0 dot to remote ESS same tell all right now on our one I should see two neighbors show IP BGP summary array is getting neighbor now one more neighbor has to come let's try pinging this address pink all right out of some problems there it's the nature phone you if you find active-active is bad it is trying to form neighbor okay so you got vgp neighbor right between r1 r2 and r3 we have neighbor similarly between r v r3 and our seventh show ID v GV summary we have neighbor similarly i will show you an arts are for show IP bgp summary it has two neighbors likewise an r6 i should find two neighbor show IP BGP summary we have neighbor so this means you know BGP is properly configure now we are trying to understand how path is selected based on attributes for the first you know let us advertise some network only their path can be selected so on r7 I'm going to I'm going to advertise this network CN r7 I am saying router bgp 50 network this is submitted so 75 door 1.0.1 mask sorry this one is not name needed mask 255.255.0.0 don't do well can mask here I also have one more network then it's 72 dot sorry 75.2 this is not like reaper OSPF rei GRP you simply type 75 dot 0 dot 0 dot 0 all 75 mega will maybe it's not like that we must exactly match the mask that you are given on the interface all right now you see let me show you one show IP interface brief these are the two networks that we have advertised now show IP BGP look for this two networks 172 dot 1/16 1 Saudi draw 2/16 this router 7 is running BGP I told you there are some attributes you know we have in BGP next top as an attribute MBD as an attribute local preference attribute weights another attribute path another attribute out of all this out of all these attributes is path must mandatory should be there next hub should be there origin should be there local preference and ma de are optional that's why that is why in our 7 local preference and weights they're optional Emily is also an optional one which is mandatory there should be some number or next hop address there should be path attribute there should be origin origin means you know from where it is coming origin this I means you know internally originating not through redistribution ie customer means coming through redistribution we will discuss about that in sometime now these are all mandatory attributes now if I'll go to r3 r3 I am in r3 now if a.type show ID BGP I am getting 75 and I told you there must be an explanation of address see there is an extra meter if there is no next hop address it cannot be a valid BGP update because next hop is what I am well known and mandatory attribute this is well known as well as mandatory it should be there for every update that is coming from neighbor on r7 since it is already from the same router it is 0.0.0.0 but if you go to r5 what will be the next hop address and are fine extra buttons will be 57 dot 0 dot 0 dot 7y and it's coming from 7 router on r3 what will be the next hop address 35 out 0.05 why it is coming from next autonomous system now you see autonomous system is also well known and mandatory yes part is also must mandatory so that's what you see here this is 75 dot one the 75 dot one is learnt on our three is learned on our three from where it's learned on r3 from where from 20 autonomous system 2000 must have learned from whom 50 path attribute this is also well-known and mandatory attribute should be there see for both the roots you have path attribute for both the roots you have next up but this is all nothing why they are optional maybe there may not be them amiri metric is called as a midi immediate option 'l local preference is optional wait is a cisco preparatory attribute you cannot find on other vendors it is also an optional 0 by default now what do you have here I I means it is IGP meaning it is advertised by BGP itself see how do you got this because we advertise on our seven on our seven we advertise using network command this network is advertised by whom hey JB know OSPF know these two networks are advertised by BGP itself that is the reason why you have I eyes if it means don't think you know it's an IP protocol eigrp are OSPF normally it means by this protocol itself here it means that so this IP is not IP protocol IE a zr p ro SP for rip it this i means this IG b means it is originating from bgp itself it is originating because of name network comment that is mentioned somewhere on some router hi gb here it means it is this networks are because somewhere on some router and bgp you have used network command not coming through redistribution from other protocol but if you'll find question mark instead of i which means it is coming from some other protocol or it is coming through redistribution i'll show you that see I have router 6 here and router 6 has 127 router 6 has 127 soil go to router bgp 40 redistribute command see reduced immune i'm saying connected if i say reduce if it kinda what are all connected to r6 show me what all networks tell me what all networks connected to are 6.30 5.11 notified or 267 and 46 see when i say they see what happens I'll go to r2 and show you that on our to show IP BGP look I'm having 46 and 67 okay 125 dot 1 1 dot if I wrote two so far I have not a sign on interface that's why it is not showing but anyway you are seeing one proof here 47 and 66 TV 7 is having question why you read this unit you reduce network command to advertise this whereas these things are coming through we're through BG bits have you used network command it says once all you dreadful sorry 75 at 1 I learned from router for that is the next hop address which was in autonomous system 30 and that autonomous system learned from autonomous system 40 that alarm system us learn from what on our system 50 in here we did use redistribution command we used what network commit that's why for that network it is having I for the networks that year that is coming through redistribution it is having question mark why question mark means incomplete incomplete means it is not true BGP zone network it is someone some other protocols network being redistributed inside some other protocol or connected it is not used it is not coming because you use network commit you didn't use net recommend you made something to bring this network that's so it has question mark alright now what is this e since there is no EGP concept now previously BGP was true different protocol now you have ib g b eb g b two flavors but previously there was a BG b Bradley bgp separately in sub-e BGP we had eg B now we don't have a concept of EBG B we have only two flavors of BGP that is ibgp re-visioning ebgp means external border gateway protocol 15 boundaries IBG be within Bond right within autonomous system so you will never find any in your life name that those stories are old stories you will not inside I in the fine version but I mean what these networks are coming because somebody use network command question mark this networks are coming because somewhere you really seem unit from somewhere you might have already submitted from another protocol or you might have redistributed the connected networks in our scenery we need a signal connected now let me add 125 s well on our six now on our two I must find we help so I to be GV c 125 is also been advertised here on this router that's why 0 let's go to router 2 and ask for another show I will be GB summary it has two neighbor router for every router for neighbor is going down coming up by BabyTV summary right there are six prefixes learned from our six what are they for prefixes from directly character and two prefix from down sonar for I should see show I could be GB yeah see these are all having question man why not coming because you use NATO command you didn't use NATO command for this Edwards alright what is this our trip failure is what is the sorry failure means this for T sakes actually is there an hour for itself correct hour for knows about 46 or not it knows that if the content but silly it is learning through bgp to sources for 46 one is b gb another one is not having again then you will have a failure are not sort of matter okay that's not an area of study also no go to our our to show IP bgp towards you have a question mark and you have i so that's what the origin attribute means origin will be there always see origin is also mandatory from where it is coming is it coming through bgp or redistributed everybody's coming through rebe gb then you will have i'ii finish because of redistribution if you have question mark so this is also a well-known mandatory attribute right let me let me show you on our three show i DBGB look in our three also one twenty five and forty six and sixty seven is having question mark and all these attributes are mandatory next half path and then origin these are all mandatory attributes whether if go to r1 and r1 I will type show IP BGP summary now this router has two neighbors a very important this place are what are one has two neighbors only stout two and another one is router three now through both the routers all the six networks will be learnt now two ways are seven will say hey I know about seventy five dot one 75.2 yr this way it can also say why are this way correct two ways like this whatever you redistributed here will be said by our this way as well as this way correct or not correct now I would like to remove the 67 and there 46 from scenario we will take only these two why unnecessarily we bring the 67 and 46 which is there on link so to filter that what I will do you know I will go on our six and I'll write router bgp 40 we said redistributed connected now but when I say read is people connected even these two links are really similar I'd want to reduce if only Lubeck so further what I can do is I can use a route map okay I'll tell you what is a node map the map that you write to decide the route this route map the map that you write from here in the route now I say route map now before I writing road map I'll read access list access list one vinai let me say 46 dot 0 dot 0 dot 0 0 are 255.255.255.0 view you don't want to redistribute 67 I'll write this and then I'll add this on the road map route map filter if I say route by filter route map filter number 1 will begin this filter is the name that I gave let me do one thing I made a mistake instead of giving in lower case if you give in upper case if you lie either understand this is a user-defined name and not a command I just give a name and say match access list match IP address match IP address what is access list number one match access list number one that's it now this what I'll do I'll call this route map called filter underwear router bgp 40 this is the command we gave previously which one redistribute connected I will cancel this I am saying hey you read this you will connected but filter what 46 and 67 you understand this I read an access list and denying call that into a road map and here I say route map name that you need to follow is filter got it so when this redistributes it will not redistribute 46 and 67 instead because it is denied in the access list now whenever you do this type of attribute change we need to do something called reset there are two types of reset hard reset and soft reset to type of resets what are they hard reset soft reset it is mentioned in Europe PPD you know if I really worry about that no when when you go through PPD you should know okay this things are covered all right that's what I want no need to really write in hard reset it softly said what is hard reset look at this this is an example of under is it clear I be BGP start I am saying refresh all the neighbors disconnect the neighbor re-establish that is hard reset disconnect the neighbor and re-establish the neighbor that is how does it see when I do hard reset to Labour's will go down and comes up you see that recent it's going down and coming up there is one more reset called soft reset what is that you say clear IP bgb star and followed by followed by soft you see that soft this soft means this will not terminate neighbors it will simply reestablish without resetting it will reestablish it won't it won't cut the neighbor relationship without cutting it you'll try to establish again that's why you know you are not seeing going down and coming up in real-world scenario they will use soft reason not hard reset when you do hard reset all have to change because you're cutting neighbor relationship she's our neighbor relationship other routers would say hey never got neighborhood so I'd that self reason is good right now now let us go to r2 and see show IV bgb it has not learned anything it will take some time show IBB he be nothing has been learned our six try vgv okay can someone say what mistake has been done now 127 is also not advertised by us no in a CLI filter 46 and 67 but I forgot to say permit any I denied for disease I denied 67 I forgot the same permit any so let us add ACL access-list one / made any now if you see you will get it now we have a signed show IP interface brief so I BBG be look one twenty fire has come but the problem is all our not best okay now all our best you see we have filter to knit words using route map route map is very very important for CCIE those were first PCIe it's very important note map on our to 'let's go and check still nodded come are for our phone has received our tool should also racino yes r2 has received okay and rr3 also has received now for our three which is near 75 or 125 75 is near only two hops for our two which is near 1/2 DB is near this is a long way this is near fine now let's go and see what is near in r1 see if you see here on diagram diagram and say you will say for r1 to go to 75 going where R 3 R 5 is near then going where r2 r4 r 6 and r7 correct for 75 Network going like this is easy then going like this great so R 1 should say hey 475 I will go I R 3 R 1 should say for 125 I will go where R 2 3 y less number of autonomous jumps if you go away R 3 there is only one two autonomous jumps 20 and 50 if you go away are two it is third if 40 and then 53 jumps that's the case for of 75 for 125 you go by a R 2 it is only two jump if you go via are three it is three jumps 20 50 and 40 now show IP BGP whatever we discussed is good but definitely it is not going to show the same what you discussed it says another route is good why it says valid all are valid but not best why not best because you have learned from ebgp which is not reachable you remember we learned ibgp will inform other ibgp the next hop address that is told ye BGP will just carry like that heebie jeebies address will be carried into ibgp this router has to say hey outer v 4 is not the next hop I myself is the next row they some something is wrong actually I should see to whale in learning show ITB GB now it's correct see 75 I'm learning through router 5 is that right 25.5 I'm also learning from 24.4 which is shorter going by a 5 is what shorter or 75 20 20 and 50 only but going by r4 is too far 30 40 and 50 so according to what we discussed here I should have valid and best but it is not best it is valid only why next up address is not a reachable address what is the comment that I need to type on r2 and r3 next up self-command very good so I'll go to our three and solve this problem I'm an r3 and say an outer bgp ten I'm saying Delta neighbor 30.1 that you yourself is the next hop likewise an r2 router bgp ten tell to the neighbor r1 then you yourself is the next hop now if you see your problem solved sorry not Feeny see one neighbor is often going down and coming up I have never only through three I should have towards okay we got the neighbor to neighbors but it says valued and based only for three is that right or not 75 if you go away three that is shortest path 475 if you go by our - it's a long path craig 'no sir for 125 if you go by a - in a short path that is why you have married and based same here also but for 13 you don't have L done based because it's a long path you understand me right now you understood how this has come this now this is the place where we are going to start learning about attributes the first attribute in BGP path selection is weight highest weight now in our example we have router one that can reach 75 via r2 as well as r3 now r1 has to decide whether to go by r3 or r2 first you check through which way weight is higher not lower higher but by default weights are zero why are outer - as well as router three so it couldn't decide based on weight next what it will do let's see the order next it will go and check the local preference the highest local preference let me assume this document the highest local preference is what makes you next visible check now for that if you see here the local preference is also type by default local preference is 100 where both the roots so now it cannot decide based on local preference there's a tie-in wait there's a tiny local preference now let's see what it will go and take now what you will do come on it will check whether it is IR question mark what is I using the Tor command or Jade whether it is coming whether it is locally originated by a network command or algebra gate logical means you know free distribute command now you see in our scenario for 75 you have two routes and both the roots have I both Hawaii if you have one I the other one customer which one it will choose i YB jeebies or network i means but here there is a tie again both are having I there is no customer since there is a time it goes to the next attribute in order what is the next attribute in order a spot now when you are singing is part it found that one a is for the shorter than the other a spot so it decided that let us go with this that's why it is showing route the three is best path to go you understand if we are not setting any attribute it is going to decide based on EA's path so that becomes a default attribute busy bees default attribute becomes a s path if something is said if I would have said wait eager of decided based on weight not based on a spot now I'm going to say wait if I said wait to r2 it will start going we are to instead of going we're on three I'm going to show you that now changing weight on our one you can change the path selection currently currently 475 the pods taking this 13.3 correct it goes through r3 by changing weight on r1 I can change the direction of the traffic flow see now routing table show IP route when I type show IP route 475 it will not have this address as the next stop it will have this address see 475 thirteen is the address it is not showing too but after changing the attribute mid-weight you will see in stuff 13.3 you will see 12.2 shall we do that right for that very simple go on the router bgp 10 this is a cisco proprietary attribute wait is a cisco proprietary attribute and this is non-transitive attribute wait is a cisco preparatory and non-transitive attribute this will not be this will not be eat tagged and sent to the next router the weight that you said the set is locally significant will not be sent to do next out that's a non-transitive weight is a non-transitive attribute now how to set that I'm going to say what is the default weight 0 bigger is good always bigger is good now what I'm going to do I'm going to say neighbor 12.0.0 dot - what's your name you want traffic to flow yr to not yr 3 why your company policy says how many policy says all traffic should go AR 2 what is the solution this is the solution you go and say r2 is my neighbor who has more weight age the default bed is zero if you give anything more than zero I will give 100 now you give importance to router 2 then Row 2 3 whenever you change the attribute like this whenever you change attribute like this we need to do one clear IP BGP star at least soft you should say resending the OSPF now what is this message digest see before we starting this before we start this lab we are doing bgp authentication now this error once it comes means it won't stop it's a BGP s error in Cisco routers see actually as indication problem will not be solved is solved long back but still it is showing bad authentication once it has come means until you restart the router this will be coming this is the bug already you found and then everyone knows well-known bug in Cisco device fine now you see show IP BGP look all traffic's are going by r2 order I guess one neighbor has gone to try to DGP neighbor summary yep see all the roots are going via router to previously does going via router 3 one more time show IV bgb why you have said more wait for that neighbor previously it was going way r3 or not 75 now even though it's a long route it is going via are to previously we're having seventy-five going with our three the routing table you will have you are having 13.3 now you have show IP route 202 cut it traffic goes where are to changing the way it changes the path selection changing the attribute changes the path selection you learn how to said wait no because there is a tie in the bay there because there is a tie breaker right in the first attribute first attribute is weight I do not go to the next and ripple you will not why that is also already a client I breaker but still I am not convinced with this out are no it is correct look even though you have two routes 13.3 as well as 12.2 which is taken too old or too is taken because it has more weight even though path is too far it is not considered before come path comes what weight tie breaker but weight is non-transitive meaning you cannot see this number hundred on next router you will not see null transitive enter you will not be thought it is locally significant to that router and it stood weights the next attribute analysis local preference if there is a tie in weight tie breakers next local preference to understand local preference what I'll do I just go and delete the weight that I said why I am deleting it there should be a tie no I want to try until it does so we will say you know clear BGP star soft now as usual traffic should flow now for 75 it should go by our 3 for 125 should go air our to show IP b GP s-- it has become normal now I deleted paid I deleted wait so it became normal 75 is going we are 3 and 1 125 going where r2 172 125 going by r2 75 it is going where our 3 became normal because I deleted vision now this local preference by default it is Android vigor is good you can sit on any router you can sit on r3 r2 or r1 anywhere against it it is transitive but partial meaning the attribute local preference that you set on one of the router in this autonomous system will be flooded to all the routers in the same autonomous system but not to the next autonomous system it is transited say for example I am sitting local preference on r3 it goes to R 1 it goes to R 2 but not to r4 r5 r6 arson transit but partially got it local preference is local to that autonomous system why it will not be sent to other autonomous system but they will be flooded with in the autonomous system whereas of 8 that we learned before it is locally significant on that router only wait is significant on that router only it is not transitive whereas local preference is transitive but partial not sent to either autonomous system right now the preference is transitive but not sent to other autonomous system within the autonomous local preference is partially transiti we cannot say non transit now transitivity still it will not sell to anyone it sends but within the data Rama system partially transitive so in order to sit on any every router or non autonomous system 10 and configure this you can see only on one round now let us let us take one example 75 is going way of each router r3 I want 75 to go via our - I want 75 to go er to this I can do in two ways you can follow any one way what is default local preference 100 if I want all traffic to go via our - I go and decrement the local preference on our three I mean I'll decrement the local preference of our three - Sophie so automatically r2 is bigger goes bigger is good otherwise what go to r2 and increment some 50 150 you make it as 150 r3 will have 100 r2 will have 115 so more bigger is preferred I will go anything now each one will do decrement our increment increment that always be like increments so what is our aim all traffic should go i r2 including 35 I go to r2 and say router bgp ten neighbor I'm getting update from our for no I'm getting a bit from work for so my neighbor is 24.0 dot zero dot for I give local preference I'm sorry so I think uh - different BGP default local person sorry this is the command BGP default local preference right BGP local preference I would like to give 200 what is default default is hundred right I say 200 so this type of neighbor comment is not needed actually there is advanced level of local preference configuration other than this which I will be showing by the end of this video for that I need neighbor in and out lot of stuffs others will come to that hotpot leader this is very simple right I am sitting local preference more for this router for our time setting more local preference and this is the command yeah that's a simple command BGP default local preference and then the number whenever we change attributes like this so what we need to do clear either hot treated or sound freezes clear IP BGP stars soft now if you'll go to r1 and C go to r1 and check our one previously 75 hours going we're out to 3 125 was going wire order to see that then previously goes like this this is previous scenario now values a set local preference on r2 or r1 I I did an r2 r2 I did see an r2 only I did it but you see on r1 will get the number wait something is going learning is notable show IP BGP so we will be somebody an r1 show.i DBGB look all traffic given 75 is going by r2 why local preference where do we set local preference not on this router we set an r2 but because it is transitive it has come on r1 we have received local preference from our tow we need sit on our bottom let's come from r2 and now all traffic's are going way R to show IP route bgb see all going way r2 seventy-five yeah that's right that's right let me show once again show ID PEP it's called a down that's why my this thing is confusion now all are going we're out on to it should go by or over to see all are going way around this is the correct state is according to your local preference all once how do you do as well as 25 ago we're out onto something is going down and coming in now that's what local preference your little preference right local preference now after local preference comes if there is a tiny local preference only then it will come and see whether it is I our question mark I means one free distributed through network so again coming to network a customer means redistributed if you have two roots one is having cost mark the other one is having I for the same network if you have two roots see for 172 narrow on sound if I network I have two roots but both are having IE if I have one I and one question mark it will take which one the one with I so in origin God is preferred more than II and he is preferred more than question mark but he will never come across the e is no more it's old protocol we have only ibgp and ebgp so this and this so that is next if there will be tie in origin next its neck city ready to take the autonomous part then if there will be yes part also same as you mean our scenery we don't have a spot same if you will have a spot same see what it does that prefers the path with the lowest metric sorry before that prefers the path with lowers origin type Louis origins type igb is lower than eg P and eg be slower than income right come on you're confusing here say to network Emil you are getting IGP no I this and this has some connection same origin actually but this is lower storagee lowest origin type it takes right now after this comes immediately you don't have a scenario for this to explain but this is what you need to know mostly our five selection will finish in four steps itself is positive in case if it comes it will come to Louis origin type if that is also same only then it comes to Ma da Emily is nothing but metric what is the default metric zero now M it is metric zero this is a meeting is not for choosing the package within an autonomous system not for choosing the path within an autonomous tough it is to choose the path between autonomous if I'll have another connection between r2 and r5 and there is no correction there is no r3 assume there is no arc right if I have to connection now if a MIDI is 50 here for our for M it is 100 here for our 5 it will choose the one with a lower mm Emily for Emily lower is better for Emily smaller is good so MVD is the only attribute that we learn now which affects the other autonomous system right now amelia is the only one which affects the other autonomous systems path selection now if you want to set a media have to set very simple go under in go under router bgp ten and say neighbor twenty four dot 0 dot 0 dot four metric I'm sorry then there is no need of saying neighbor here simply say set me free set me trick after neighborhood set metric said I shall metric no BG be the comment goes like this default metric and then the metric number this is how we set metric amédée we called SMED MBD this service area midi media exit discriminator to say which media of each router it has to exceed we said something like this but this is the only midday attribute that we are learning which will affect other not renova cyst so other autonomous system to choose says if this router are under the notify there are two panel collections two redundant connections you need a mealy if you have multihoming to choose one is P then the other one you said a MIDI right okay now in the in our scenario we cannot test a mealy this is how we set a MIDI now hope you understood the six metric that we need to know first one we started with wait actually next hop address itself is a attribute without next hop address none of the route will be considered as valid but that is not mentioned in the attribute list that is one second one is weight third one is local preference third always sorry fourth one is locally originated fifth one is EA's path six for its lowest origin type sixth one is a MIDI right so six attributes are very important the other things you know they will be happening automatically which is not under our control these are all the things that we can do local versions you can tune it ma D is included wait you can tune it right so next you know we are going to do same thing that you learn now in local preference or with MBD along with route map right let's take a scenario over our one show IV BG b now right it is not learning properly let me reset the router and get back right we are on our one show it could be GP but still he does not learn through our to show ibgp neighbor show a beauty summary right here we got four four routes show ID BG b vp see we said bade no but the weight is not really considered why there is a tiebreaker before we that is a tour of a system so it is going where lowest autonomous now forget about wait let us say close automaton the system now according to autonomous system path selection 475 which is the gateway router to RO 2 3 so 475 Network which is the gateway router 3 are out of to row 2 3 4 125 out of 2 that's what you are seeing here now with the help of local preference I am going to change just opposite what is that for 7513 tool will be based for 75 proto 2 will become based for 125 3 will become being based how my setting local preference with the help of road map I can do this with the help of road map I can make 75 to go via to 125 to go by our 13 even though it is a long route why before checking is path a local preference will be checked if you change local preference it is possible now how to do this when you make it out man see what I'm going to do I'm going to do on router 2 or out of 3 I do thrust this on route 3 why if you do in one router that is enough it will be flooded to all the other routers local preference is significant on that autonomous system on our three I'm going to do this if I do in one router it will affect the other outlets because it is not only a local City local preference it is locally significance of that autonomous now what's her name 75 should go air ro to do what I can do for that on our three and decrease the priority only for some effect automatically 75 will go wire or two we are to have 100 on our three you only 475 network for on our three only buy a 75 Network if I decrease the priority if I decrease the local preference then our one will start sending by r2 because our 1,200 I'll make local preference for 75 50 on our three on the same router only I'll make 150 for 125 I want to define is also learned via this way I'll give more preference so 125 will go away at this place 75 will go I this way without touching r2 r1 I can do this I already access less the aim is what 172 a 125 should go by r r3 from r1 + 75 should go AR to for r1 which is not a default situation scenario by default what we see in r1 is this 75 is going away r3 125 is going by r2 now it is going to be opposite what we are trying to do local preference you can do on any router so I am doing on our three for that I'm writing an ACS access list are made reactions list 10 per mate prior made and copy this 0 dot 0 dot 255 dot 255 when this okay I'm just adding okay this and then this I'm just grouping the network with the help of access left I'll write one another access list called 20 that will have 125 not to one 25.1 to access let's I have written one thing I forgot in the first exercise what is that access list 10 permit oh another minor minor minor mates permit statement their mind about this now this is death please write it out map road map route map I'll say fil T IP address so if match IP address match IP address access list 10 if this match happens what need to do it has to which 1010 is 75 right 20 75 75 do you want to go away are three you don't want to go out break so what do you do if this match happens said local preference as 50 unison what I am doing you know no preference here whereas the other outer has a bigger preference hundred up to a hundred for this right next one route map filter 20 C that is 10 this is 20 if you can say any number after filled it takes 10 second number I am giving 20 match IP address 20 I want traffic what 20 is matching with what 125 I want 125 go by our this router so what I need to say if the match happens set local preference to 200 the other one is having hundred now this is having 200 so 125 will go away the spinner NSN the logit now for the other traffic's you simply write crowd map thirty simply you think you need to create one it is like permit any statement proud map is nothing but an advanced access list to define the route that has to be selected for path selection now you see let's verify show IP route map all right we're on for sure off man see these are the road maps that you created first first we created with siegen's number 10 we are matching with 10 access list setting local preferred 52nd De Sica's number 20 matching the access list 20 setting local preference 220 means 125 more preference given 10 mins 75 less preference so this router will not forward 75 because less prefer wind out 125 because more prefer alright next this is not in error you need to go to router mode router bgp 10 I am saying whenever you receive route from neighbor 35 dot 0 dot 0 dot 5 use the route map that I returned what is the route map name field use a road map and apply the policy in the update when the update comes from 37.5 apply this road map policy where it is coming it is coming inside our 3 or outside entry from our 5 inside so the inner doubt is very important in when our bread comes from file inside apply this roadmap policy that's the meaning when I route when having a winner when a route comes from an update comes from this particular neighbor inside this r3 apply this policy filled fill disease out map that we created now what I am going to do is I'm going to copy this clear right without star once I'll restart the behaving process so what do we see here 125 i watch 75 is going back no no no still not still not reflected in local preference not reflected it is not reflected which means there is some problem go to r3 there's some problem clear IP route BGP I have not clear either out star clear I will be G be sharp and clear IV BGP that's what I was know wondering why is that did reflect all right let's go to our word and shake now try biggie somebody calm neighbor first let's wait hog at the forum labor right now let's verify show maybe somebody we have two neighbors try baby look 75 is going where r2 125 is going where tray which was opposite why it is because of local preference the local preference that you said in one one drought and will affect the all the other routers that is then their autonomous system this is what we said if wondered if it matches give 200 if served if it matches you give 50 where did we say we say done are three hope you understood how BGP attribute works thanks for watching this video see you in the next video bye

Channel: Jayachandran

Views: 88,962

Rating: 4.8169012 out of 5

Keywords: -BGP-, -Jayachandran-

Id: qJ9RgfCP38s

Length: 75min 41sec (4541 seconds)

Published: Tue Nov 20 2012