3. Troubleshooting Route Maps - Cisco CCNP Enterprise ENARSI (300-410)

there's no doubt we understand the idea of course of routes and redistribution but what can we do to affect those the way that we want to we'll find out more next right here on it pro tv you're watching it all right we are jumping into the realm of route maps today and here to give us better context on when we would actually use them and how we're going to use them effectively anthony saquara all right anthony there's no doubt that as we come from the ccna part of of our studies and learning more than likely if anything kind of gets a little bit confusing of course redistribution is probably the big one but right after that it's going to be the use of route maps and where they're actually used effectively and and how do we actually get them to actually work the same way that we want them to so anthony where are we going to begin yeah you know that's a great point ronnie i didn't think about that you know route maps can be a little confusing for students when they're first starting out and then you just reminded me that one of their biggest confusions is they're used for so many different things ronnie's very handy and one of the things that ronnie can fix is automobiles and i bet you even ronnie in the automobile industry has used duct tape i always like to think of route maps as like the duct tape inside of our routing studies because we can use this tool for so many different things we can use it for attribute manipulation in border gateway protocol we can use it to tag prefixes in ospf we can use it to do policy-based routing on a router these are just some right off the top of my head that i'm kind of randomly picking when we go across all the different product protocols remember now route maps are not specific therefore to any one job and they're also not specific to any one protocol that's why we're covering them in this section of our anarchy studies now you actually mentioned something at the this idea of actually doing policy uh type of routing here for a moment can you explain that a little bit more because that may be the first time maybe somebody coming from the ccna has really even heard about that too much yeah and you know what great news is we get to shoot an entire episode dedicated to that which i think is so valuable because that is kind of one of those mind melts for people relatively new to cisco networking the policy-based routing feature is so cool ronnie it allows us to construct a route map that's going to give the instructions for how routing is going to go and then we end up applying this with a policy routing command underneath the interface so we can take a cisco router and make it route however we want it to we can override the default routing table and you might say well isn't that what a static route is for well this goes well beyond static routing this allows us to go in and like do multiple things like we can see that the traffic is for a certain destination and we can add a quality of service marking and then send it on some like different path so the sky's the limit essentially and it's a really exciting feature now anthony that sounds almost like trying to set up some conditions that we can actually route by so we want something to go uh from one router to to a specific router it sounds like i can actually do some conditions on it is that what you're talking about in terms of policy absolutely and and that all and that brings us back to you know our main topic here which is route maps that all really just um is that that capability that amazing policy based routing capability is really all because of the magic of a route map which is uh an if then kind of programmatic logic in fact what do you say ronnie should we jump on the equipment and just show everyone uh the route map in action i often find that this is one of those uh kind of technologies that really is best demonstrated as a way of teaching it right so uh here we are on this r3 device i just quickly spun up some devices inside of cisco's viral the topology don't worry about it okay this is just really to focus in on route maps um just a simple topology that i spun up and you can see i've done the show ipbgp on this device and when we look in the routing table for bgp in fact let me back up what we're looking at right here is the bgp topology table and so it's not the routing table but when we look in the bgp topology table we can see this prefix right here for one nine two one six eight zero one slash thirty two and we can see sure enough by default it has a cisco weight value of zero so the default weight boy wouldn't this be great for weight watchers is zero and the uh default weight by the way just out of curiosity at this point for a prefix that we advertise notice is going to be 32 768 and a higher weight is the first thing that a cisco router would prefer when choosing the best path so weight's a very important powerful value in border gateway protocol and we can see again zero is the default for routes we learn and then 32 768 is the default weight for routes we generate well what if we wanted to give that incoming 19216801 prefix a higher weight how the heck would you do that well a route map comes to the rescue like it does in so many different cases so the first thing that i'm going to do and i'm glad we're getting a sneak peek at some of this bgp related stuff the very first thing that i'm going to do here is i'm going to do what's called a prefix list a prefix list is a very very cool flexible straightforward way in which to identify prefixes instead of having to use an access list which is a pretty cumbersome way to do it so i'm going to say iprefix list and i'll be real silly here and just call it my list and then i'll get some context sensitive help i want to permit and then i give the prefix and the prefix masked lengths all in one handy statement so i'm going to say 192.168.0.1 32. wow what an easy simple way to call out a particular prefix and now the syntax we're really interested in i say route map and give it a name again not being creative i'll call it my map and then our context sensitive help we do a permit or deny on the route map which would have like filtering logic if you were using this to filter but in our case we're using it to set the weight to a custom value for this incoming prefix so i'm going to say route map my map permit and then what's next we can do a sequence number so i can start the sequence numbering at 20 if i wanted to not start at the default of 10. now we're in route map configuration mode as you can see and we match on traffic this is kind of like the if part of the if then programmatic logic so i say match ip address and it was called my list oh in fact i think i have to say match ip address prefix list there we go my list so if we match on the prefix specified in that prefix list which was of course 192.16801 the routing question here then i'm going to say set the weight and let's do a number that would jump out at us how about 7777 so look at that an if then programmatic structure called a route map and in this case we're using it to set a bgp attribute which by the way is a super real world uh you know application of this feature so ronnie there's a big problem here though if i ended this now and in fact uh this would be really dramatically witnessed if we were learning like thousands of prefixes which is very realistic for bgp from our neighbor if i ended this now and attached this route map into the bgp config sure it would set the weight to 7776 for that prefix i called out but it would then deny all of the other prefixes from coming into the router because there is an implicit deny here just like we have with an access list so what i need to do here is i need to just use my up arrow i'll do a line called line 40 that is just to permit everything so notice i have that kind of empty line that empty segment of the route map at the end and that would permit all other prefixes the way i'm using the route map now anthony with this single line that actually is going to give us that permit all is there sort of like in the access list where we can actually put that in and then put in like a keyboard log at the end is that something that can be done so that we can see if it's actually working or not uh that isn't done but the great news is that we have uh logging on the route map nice so here you can see it ronnie so we don't have to do anything special when i do my show route map it will give you a breakdown of the route map that you've constructed and notice there's you know uh policy routing match information right built right in there so when we use the route map from a policy routing perspective we have a built-in counter all right now anthony is this uh sort of like also i keep going back to access list because that's what ccna students are probably going to be most uh comfortable with trying to compare that to from what you've actually from what we've seen so far so you've actually created the route map so where are we going to apply this didn't you say it's in the router config or is it on the interface that we would actually apply something like this great call so um i love what you said there you know a lot like access lists right um this thing's all fancy and beautiful and it's useless because right now it's not applied anywhere and i love what you brought up there ronnie where do we apply it would it be here would it be there well it all depends what are we doing with it right so we are manipulating a bgp attribute so we're going to be applying this in bgp but if this were a policy uh routing scenario then we would be applying this to none other than uh the policy route statement that's under the interface so oh and by the way ronnie you asked a great question about logging um if you wanted logging right associated with details of the route map one fun way to go would be to use an access list and turn logging on for that acl entry yeah so now you're getting the acl logging and that acl of course is used in the route map all right so what we're going to do here ronnie is we're going to get this thing applied i mean after all this is all fun and wonderful if it actually works now just to make sure there's nothing up my sleeve let's do that show ipbgp one more time and we want to make sure that the 19216801 prefix does indeed have the weight of zero still and we hope to change that with the work that we've done in the route map so i'm gonna go router bgp one i am going to say neighbor 10.0.0.5 i do believe we are neighboring with and i'm going to say oh look at that it doesn't allow me to enter the route map command there because we've actually done the address family configuration mode style here in bgp don't get freaked out by this if you haven't seen it in a while or never seen it um we'll be covering this in great depth with you here in an rc but i just need to go in there and do my statement so i go neighbor 10 0 0 5 and then i say route map and it was my map and we have to give a direction so we want this to apply to incoming routes and that error right there specify the peer group whatever this just means that i did the wrong neighbor ip address there and so let me just do show run pipe section bgp and i just need to remember what neighbor ip address that i'm working with and it's i wasn't even close it's 1009. all right so here we go we're going to go neighbor 10 0 0 9 and we're going to do route map in i'm going to end and we're going to do our show ipbgp and this is a point ronnie where we have to remember that bgp isn't all about convergence and so that can be really tricky when troubleshooting so we're kind of troubleshooting this route map right now aren't we because we applied it and we've got no change for this incoming prefix yikes but remember i went and looked pretty quickly so i chatted with you for about 30 seconds there and that was enough time to have the convergence kick in and notice we got a nice lucky sevens seven seven seven seven wait for that prefix in question now going back to your neighbor statement that you did so what we're actually saying when we do the inbound there is that is this an update to my router that's coming in or am i actually pushing this out that the other routers are actually able to see yeah so let's envision that ronnie so we in fact let's do this show run pipe section bgp uh let's take a look at the command and there is the command and it's a bgp command neighbor the neighbor id route map my map in so what's exactly happening here ronnie is we have the prefixes coming in via the 1009 hearing and the route map is applied as bgp updates are coming in so this local router r3 it looked at the updates coming in to see if any were involving the 19216801 prefix when it saw that update it set the weight of that prefix to the all sevens and then installed it into the bgp topology table now does that get moved into the routing table well if everything's okay with the reachability and stuff involving that prefix sure and there we can see that prefix in the routing table notice it's pretty interesting that the uh the weight of course isn't shown there right the weight is not something that shows up in the routing table the way to remember is in the bgp topology table there it is and that could help pick this prefix to be advertised into the routing table but it's not shown in the routing table so yeah sorry about that i i do have a question uh that uh it's now that we've actually affected this on your uh third router i'll call it router three here now that we've affected it there do i need to consistently go throughout my my particular interior bgp to ensure that i have the same thing all the way around or is this just a router by router um route map that we actually use yeah so excellent question so the way we did this we constructed a route map and set that route map for the directionality right on appearing of updates to influence those and that in this example would only be done here and this is why i say that weight remember is a locally significant value right so when this r3 device sends this update on to let's say r4 r4 is going to receive it and it's going to strip any weight value because by default because again uh wait a minute whoa back up the truck to be technically accurate here the weight isn't even sent right okay so yeah this uh this r3 device is not going to be sending the weight attribute along with the prefix in bgp the router creates the weight and we know that would be zero by default when the r4 device receives it so this was an interesting example ronnie in that uh not a lot of workload on us we might just be doing this on this single router and remember by the way it's worth just kind of refreshing about this remember the weight is a very very very fast and efficient surefire way it's the first thing the local router would look at if we had a bunch of different paths ronnie and bgp to get to that prefix the weight is the really quick tiebreaker that we can set all right anthony well thank you again for helping us to kind of get started here in terms of route maps and being able to actually be able to use them a little bit more effectively we can actually apply it here as well as some of the other contexts that anthony had mentioned but make sure you pay attention them as you're likely to see them again not only here but also of course on questions on the anarchy exam well that will do it for this picker episode then signing off for it pro tv i'm your host ronnie wong and i'm anthony saguerra stay tuned right here for more of your cisco and rc show thank you for watching i t pro tv

Channel: Coral Cert

Views: 28

Keywords: Coral Cert, CyberCourses, Cisco, ENARSI, Networking, Help Desk, System Administrator, Cybrary

Id: cjlVcx1MalI

Length: 19min 24sec (1164 seconds)

Published: Mon May 17 2021