Conditional Mark Routing Made Easy

Conditional mark routing

[Music] it's important for us to note that in any routing protocol default routes aren't created equal now what do I mean by that I mean that when we look at what's going on in our environment there are going to be different ways that we can generate default prefixes of the ways that we've been talking about up to this point have been involving rip version 2 and we've been talking about the fact that we could just go under a writing process and use the default information originated command now that generates a default route but that default route is going to be generated irregardless of whether or not there's an entry in the routing table for a default route and it also is just going to be generated with no basic fundamental criteria ie there's no conditional aspect to it and that's what I want to talk about right now I want to talk about the idea of content of the idea of conditional default routes let me double check to make sure that my console here is situated the way I want and it is so here's the situation what I want to do is I'm going to generate or advertise an idea of a default route on r1 now the default prefix or the default route that I want to configure on r1 is going to be again just in all zeros prefix 0 dot 0 dot 0 dot 0 slash 0 and ultimately it will be advertised out and up and I will end up having a load balancing scenario on r22 whereby I think I can use serial to slash 0 and serial to slash one to reach the default prefix now what I want to do is I want to make this a conditional default route I'm going to say I want to make it conditional on the loopback address of our twenty appearing in my rib on our one so that address and we can't see it here it's going to be one seven 2.16 dot twenty twenty now what I'm going to do is I want to cut over to r1 and see if that prefix is actually in my routing table show IP route and I'm going to see one seven two sixteen twenty twenty and there it is it's actually in my routing table now what I'm going to do is I want to create a criteria by which I can design and deploy this conditional default route and it's going to require a tool that we haven't spent much talk and time talking about right now up to this point referred to as a route map now in a route map I can actually create criteria that I want to do matching on now what we're going to do is I'm going to find myself in a situation right now where I'm going to be using an IP prefix list and a route map in unison with the default information originate command so let's take a look and see what that's going to come and look like well first what I want to do is I want to be able to match on that prefix that I was talking about I want to be able to match on this prefix right here and so long as this prefix is in my routing table on our one I want to generate a default route should that prefix disappear from my routing table I want to see generation generating that default route there is how we're defining this conditional State so on the condition that the prefix 172 16 2000 slash 24 appears in my routing table is the criteria by which I'm going to generate this default route should it disappear I want to stop now I'm gonna match that using an IP prefix list now the way I want to do this I want to say prefix list and I'm going to say L o 0 of are 20 so the loopback zero of our 20 let's say sequence 10 and what I'm going to say is I'm going to permit and I want to match on 1 7 2 16 2002 / 24 prefix because that's what I know is being advertised to me now what I want to do is I want to create this route map idea so when I create the route map it's going to be route - map and I'm going to say I want to track the yellow 0 interface of underscore R 20 and I'm going to say permit 10 now how do I track it well I'm going to use the match IP address feature but I want to match on an IP address prefix list so prefix - list and then list my name well the name that I want to match on is going to be loopback underscore of underscore R 20 and press Enter so now I have my route map do show route - map we see I'm matching this prefix list show IP prefix - list and I can see the prefix is matching 172 16 20.0 so how do I deploy this well I deploy it under my router process so router rip what I want to say here is this default in from default - information originated and what I want to do is I want to match on a route map and that's one of the features actually is the only option I have here and say route map and the route map that I want to match on is going to be this idea of track underscore l o0 of our 20 so let's plug that in there and we'll hit enter let's go ahead and clear our process here clear IP route star now once this has been cleared let's see if we're generating this loopback address so let's go up to r2 and say show IP route and see if we have a static default route we have a gateway of last resort it's not a static excuse me but it is a rip route that we're advertising and it's coming from 10 1 to 10 11 which is cat 1 so let's go over to cat one and see what cat 1 says show IP route we can see the same prefix that's coming from r1 so we are generating it now what would I want to do is I want to go over to r1 and I'm going to say show IP route and what I want to look at specifically here is going to be the route for 1 7 to 16 2002 the routing table now what I'm going to do is I'm going to go to our 20 and I'm going to go to that interface show IP interface brief he assigned what I'm going to do is I'm going to come up here and I'm going to say I want to disable this loopback 0 interface so config T interface l o0 shut now that should stop that prefix from being advertised let's cut over to r1 show IP route 1 7 2 16 2008 snow longer in my routing table so now the question is is r1 going to advertise that loopback prefix so show IP route and let's see what we have in the table here and notice now on r2 nor on cat 1 show IP route zero zero zero zero I have nothing in my routing table now the moment I come back over to our 10 and say no shut and bring that interface back up what we should ultimately start seeing here is first of all it will return to the routing table on r1 let's give it some time make sure I executed the right command I'm 20 no shut interfaces up there it is in my routing table now that I have it in my routing table show IP route zero zero zero zero and we now have it in our table and it's also being advertised to us from cat one when we go to cat one execute the same command and it's being advertised from r1 so this illustrates exactly what goes into the idea of a conditional default route now another criteria is is that we also have the ability to be able to use reliability now being able to track reliability with regard to reach ability on and print on an interface means I have actual reach ability information not just the fact that it's in my routing table right now all we're doing is we're looking at our routing table using that IP prefix list and as long as we see the prefix that we specified we're going to generate the default route the moment that address disappears that's not going that's going to cause an issue with regard to us being able to to create that default route but it has absolutely nothing to do with reach ability the moment we start looking at reliability and default routes then what we're going to do is we're going to find ourselves identifying a new tool we've talked about route maps we've talked about the default information command we've talked about IP prefix lists next what we're going to do is we're going to spend a little bit time talking about something called an IP SLA an IP service level agreement and we'll do that in the next video I'll see you guys there goodbye