Cisco Loopback Interfaces Tutorial

in this lecture you'll learn about loopback interfaces loopback interface is a logical interface and allows you to assign an IP address to a router or a layer 3 switch which is not tied to a physical interface because we don't have any physical attributes that can feel loop back interfaces never go down route backs are logical so it's impossible for them to physically be in the same subnet as other devices so they're usually assigned a / 32 subnet mask to avoid wasting IP addresses that's a standard it's best practice to are saying and loopback interface on all of your drivers and all of your layer 3 switches the loopback is commonly used for traffic that terminates on the router itself that could be most commonly at management traffic also for other things like voice over IP if you need to send voice over IP traffic to the router also for bgp peering etc that provides redundancy if for our multiple paths to the router you'll see how that works in a second the loopback is also used to identify the router in OSPF because the loopback address is used as the router ID so you'll achieve us when we do the OSPF section when you're looking at the OSPF database etc you'll see routers being identified by the router ID which is the highest loopback address on that router the same with back interface is usually used for multiple tasks for example if you need to send traffic to the router for management and for BGP we'll usually just have one loopback interface and use the same IP address for everything multiple route box can be configured though it's not common we don't normally do that it's usually only done for special use cases where an additional back is required so not standard ok so here you'll see an example of why we're using a loopback we've got a PC let's see which is behind our four and it's got IP address 10.1 dot 2.10 and we want to connect to the r1 router to manage it well we've got two paths that we can get to r1 via our 4 from we can either go along the top half or we can go along the bottom path but if the top path goes down we can't connect to the 10000 dot one IP address and our one that's down if the bottom path goes down we can't connect 1000 3.1 so we're gonna use a loopback so that way we get a single IP address that we can use to connect to r1 even if one of those paths goes down so what we do is we add interface some loopback 0 and we give it I P address and our example 192.168.1.1 / 32 you can use any IP address you want for the loopback and we then advertise that in the routing protocol our 4 will then learn the two paths that it can use to get to one name two dot one sixty eight dot one dot one and it will use whichever one has got the lowest cost or both if they're got equal costs and our four can still connect to one name to don't one sixty eight dot one dot one even if either path goes down so this is useful for management and it's really critical for other things like BGP and IP telephony let's say that we're sending IP telephony traffic from behind our four to our one we want to make sure that it's always gonna get there even if one of the paths goes down so we don't direct it a physical address on r1 which can go down we direct at the logical address and that way even if one path goes down the traffic is still gonna get there across the other path so that's why we use a loop ax so let's configure this in the lab it's gonna be a quick and easy lab we'll do it right now so I'm gonna put the loopback interface 192.168.1.1 IP address / 32 on r1 we'll see how our four has got the two paths to get there okay so I'm on the labem on our four here and I'll just check I've got ya GRP running everywhere so I'll do a show IP route and I can see I've got an ERP route going out fast ethernet to slash 0 which is via r5 and I've got other ERP lights going out fast 0 0 which is r3 so I want to have two different paths available with one IP address that I can use across those two different paths to get to r1 so I go in r1 and I do a show IP interface brief I've just got my physical interfaces configured there right now so I'll go to global configuration and then to create a back interface the command is just interface loopback and then the number you want to use that creates the interface as well as taking you to the configuration mode for the interface and notice the interface goes up immediately because it is a loopback there's no need to do a no shutdown if I do I know shut down it won't do any harm through that's okay okay I need to configure the IP address on here so your IP address I was gonna give it one thing two dot one sixty eight dot one dot one and I'll follow best practice of using a slash for e2 subnet mask so that's 255 dot 255 dot 255 dot 255 so that is my loopback interface configured and given an IP address I also need to make sure that it's being advertised and my routing protocol so I'll do a do show run and for this section E I gr p just to check my edgy IP config and I can see I'm using a IG RP 100 and it's just network tender order order over is included in there right now so I need to include my loopback address as well so I'll go router aig RP 100 and then network 192.168.1.0 one and it's a wildcard mask that's the inverse of a subnet mask so 0.0 0.0 and hit enter and now if I go back over to our for EIG our P converges pretty quickly so let's see if the route is there yet yeah it's very already I've got a route going to one name 2.1 succeed got 1.1 but it's two paths but one of them has got a better cost so that's why it's with fastethernet 0/0 path but is made it into the routing table right now I can ping one name 2.1 succeed got 1.1 and that works and if i trace to one name two dot one sixty eight dot one dot one i can see that it's going along the top path with the next heart of 10.1.1.10 that was out interface fastethernet 0/0 so let's check that I can feel over and still get to the loopback so I'll go config T on here and go to interface faster zero slash zero and I'm gonna shut down our interface so that first path is not gonna be available anymore I see my ei GRP adjacency going down and now if I do a sure IP route so before the right to the loopback was going via fastethernet 0/0 if I do show IP right now I can see that it's in the routing table from E I GRP again and now it's failed over to the other path it's going to use fast ethernet to slash zero so I can still ping 192.168.1.1 and if I trace right to it I'm gonna see it going down the bottom path via r5 okay so that's why we want to use a loop backs so that we can get to our routers no matter what path we've got available still using that same IP address thanks for watching if you want to get hands-on practice with cisco networks for free then you can download my 400 Paige CCNA lab guide which you can see above my head right now also check out the video about my CCNA course it's highest rated course online thanks

Channel: Flackbox

Views: 17,916

Keywords: cisco, ccna, loopback interface, loopback address explained, loopback address

Id: h3LC_iITL18

Length: 9min 11sec (551 seconds)

Published: Tue Mar 10 2020