CCIE Topic: 1.2h Route Redistribution

hey everyone i'm charles judd and in this video we're going to look at the 1.2 h topic of route redistribution first we'll examine the concept of a seed metric and then we'll look at both mutual route redistribution and route redistribution using route maps when we look at the different routing protocol options we know that they have various ways that they calculate the best path to a particular destination and that's a measure that we call the metric so for example eigrp uses a metric based on bandwidth and delay by default while ospf is based on interface cost when we start redistributing routing protocols into one another this can be problematic because there's no correlation between the different metrics that are used and that's why we use something called a seed metric and a seed metric is just simply a metric value that's assigned to a redistributed route we can do that manually or we can allow those to be automatically configured if we don't specify and assign the seed metric manually when we're redistributing then ios has certain defaults that are going to be assigned depending on the routing protocol combination in this table you can see a few of our most widely used protocols and the default ios seed metrics so for example you can see that by default a route redistributed into both rip and eigrp are going to have a default seed metric of infinity meaning that any route redistributed between these protocols is going to be considered unreachable and those routes will not be advertised to neighboring routers so what that means is that if we're redistributing into these protocols we must have a metric value manually configured if we want those routes to be valid when redistributing into ospf both rip and eigrp routes will have a default seed metric of 20 while bgp routes have a default seed metric of one and when we redistribute any igp into bgp you can see that the igp routes original metric value is going to be used as the seed metric so here's the topology that we're going to be working with and first we're going to take a look at mutual route redistribution this means that we're going to inject routes from eigrp into ospf and vice versa you can see that we have three routers here we have r1 found in ospf area zero we have r3 in eigrp autonomous system number one and r2 has an interface connected to each of those autonomous systems r2 is where we're going to configure our mutual route redistribution if we connect to router 2 and say show run pipe 2 section router this is going to show us the current ospf and eigrp configuration that's in place so here you can see that the eigrp process is routing for the network connected to gig 0-1 and the ospf process is running for our local loopback interface and for the network connected to gig 0-0 what we want to do is to perform mutual route redistribution we want to distribute eigrp learned routes into ospf and ospf learned routes into eigrp so let's go to r1 and let's say show iprout and you can see that we have no awareness here of our eigrp routes we only see those routes known by ospf if we go to r3 and we do the same we're going to see a similar story here we only know about eigrp learned routes so let's go back to r2 and let's also say show ip eigrp topology and this is going to specifically show us routes in the eigrp topology table now notice we only see our eigrp learned routes at the moment but once we redistribute ospf into eigrp we should see those listed here as well so first let's go under router eigrp autonomous system number one and we want to say redistribute ospf process id1 let's hit enter here and then let's say do show ipeigrp topology and notice that we still don't see any additional routes and that's because of the default seed metric that we previously discussed remember that when we redistribute into eigrp the default seed metric value is going to be set to infinity which is why our routes are not showing up here in the eigrp topology table so we need to manually specify a metric for this redistribution and we have a few options for that we can specify a metric using a route map we can add a metric configuration at the end of our redistribute command that we originally entered or we can set a global default metric for any protocols being redistributed into eigrp and the best practice recommendation from cisco is to set a default metric when we're redistributing so let's do that we're still under router eigrp configuration mode and the way that we set that is we say default hyphen metric and you can see that first we indicate the bandwidth on a gig link we'll set that to 1 million kilobits per second next is our delay value and i'll set that to 1 then we have the reliability i want to say we are 100 reliable by setting that to 255 then we have our load value and i'm going to say that we are minimally loaded with a value of 1 and finally the mtu and i'll use the default of 1500 when i hit enter now these are the default metric values that are going to be used for any route redistributed into eigrp so now if we again say do show ip eigrp topology now we do see some new routes here we're seeing routes learned via ospf let's go over to r3 which is in our eigrp autonomous system number and let's say show ip route and you'll notice that we now see new routes with the ex status code listed here and if we scroll up a bit to see our status code table you'll see that ex stands for eigrp external that means that although these routes are known by eigrp they were sourced somewhere outside of the eigrp autonomous system which of course in our case is ospf so that is exactly what we would expect to see now let's go back to r2 and let's complete our mutual route redistribution and we'll do that by now injecting eigrp routes into our ospf process so let's say router ospf one and we will say redistribute eigrp autonomous system one and that's all we have to do we can hit enter remember that when we're redistributing eigrp into ospf the default metric is going to be 20 so we don't have to explicitly configure a metric here if we go over to router 1 and we again say show ip route this time you'll see that we have some routes with the e 2 code listed at the beginning e2 being ospf external type 2 routes this again indicates that these routes were learned externally so we should now be able to ping the loopback address of router 3. we should be able to ping 3.3.3 and we can do that that is successful now one quick thing to show you as well if we go over to router 2 and let me break out of here and clear off just a little bit of room for us let's say show run type 2 section router ospf and i want to point out the redistribute command you'll see that at the end of that at the end of our redistribute eigrp command it has added the keyword subnets this is the default behavior in newer ios versions but if you're running an older ios you will need to specifically issue the subnet's keyword if you don't do that then any routes that do not have a classful mask are not going to be redistributed so that's just something to remember depending on your ios version again i did not have this keyword but ios automatically added it for me i'll also say that if you're redistributing into ospf with ipv6 there is no subnets option because ipv6 has no concept of classful networks one more important thing that we often do when we're performing route redistribution is to filter out certain routes one way that we can do that is by using a route map so let's briefly look at that if we go over to r1 and we again take a look at our ip routing table we again see our three e2 routes listed here and one of those is for the loopback address of router 3 the 3.3.3.3 address let's say we want to filter out this loopback interface that we're seeing from r3 we can go back to r2 and we can do that with a very simple route map and access control list so let's create access hyphen list one we'll say permits because we're just identifying the traffic 3.3.3.3 all zeroes mask and we'll hit enter to create that acl now we can create a route map by saying route hyphen map i'll name that loopback and i want to say deny i'll make that sequence number 10 and now i can use a match statement i'll say match ip address and i want to match that to acl number one now let's create our permit statement because remember we have an implicit deny all at the end of that so we'll say route hyphen map loopback permit sequence number 20 to make sure that this is added at the end of our route map now we can simply apply this route map to our redistribute command under our ospf process so let's go under router ospf 1 and again i'm going to repeat the redistribute command and i'm going to append the route map to the end of that so i'll say redistribute eigrp 1. if you look at contextual help we want to use the route hyphen map keyword that we see here so we'll say route hyphen map followed by the name of that route map which is of course loopback now if we hit enter and we go back to r1 let's see if this is working for us let's again say show iprout and this time we only see two of those e2 routes we see 20.1.1.0 and the 192.168.1.0 network that is attached to r3 we have successfully filtered out the 3.3.3.3 network and it is no longer being redistributed into ospf now of course there are other filtering options that may be appropriate depending on your use case or your implementation you can do things such as route maps with tags you can manually set artificially high metrics there's lots of other ways that you can filter and optimize this let's also quickly take a look at ipv6 because there are a couple of additional considerations that i want to point out as i've already said one of those is the fact that if you're redistributing into ospf even with an older version of ios there is no subnets option because ipv6 doesn't use classful networks the other consideration is that by default ipv6 will not include connected routes for a protocol being redistributed into another protocol here's our topology basically the exact same thing except we're using ipv6 addressing let's perform mutual route redistribution here with ipv6 again pretty much the same configuration as ipv4 but we do need to take into consideration the connected route redistribution caveat that i mentioned also note that just to save time i've already configured the default eigrp metric here for ipv6 as we already looked at doing with ipv4 so let's go to router 1 and let's say show ipv6 route and from here we're only going to see ospf learned routes we're not going to see any eigrp learned routes and likewise if we go to router 3 and do the same thing we're only going to see our eigrp routes we're not going to see any of those from ospf so let's go to r2 and from here let's say ipv6 router yeah grp one and we want to say redistribute we want to redistribute ospf process id1 and if we take a look at contextual help we want to use the keyword include hyphen connected that's going to take care of that additional issue that i mentioned we need to add this on when we're redistributing ipv6 networks let's hit enter and let's do the same for our eigrp so ipv6 router ospf one we want to redistribute eigrp autonomous system number one and again we want to say include hyphen connected now again i'll point out that the subnet's keyword is not available when we're using ipv6 because again we don't use classful networks so i'll hit enter and now we have performed our mutual route redistribution we should have complete awareness of all of our networks so let's go back to r1 and let's again say show ipv6 route and we do see our three external routes listed here as o e2 or ospf external type 2 routes if we go back to r3 and we say show ipv6 route here we likewise will see our eigrp external learned routes and we're seeing all three of those listed here with the status code ex for external eigrp so that's a look at route redistribution i hope you found this content useful and i want to thank you sincerely for watching

Channel: Charles Judd

Views: 1,087

Keywords: cisco, ccie, cisco enarsi, ccie enterprise infrastructure, cisco enarsi 300-410, cisco encor 350-401, ccie lab, my ccie journey, ccie training, ccie blueprint, section 1.2, routing concepts, 1.2 routing concepts, cisco routing, routing table, route maps, eigrp, ospf, bgp, route redistribution

Id: irYeRVFSRUY

Length: 15min 7sec (907 seconds)

Published: Mon Sep 14 2020