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This is one of multiple videos discussing static routing.

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So notice what happens now when we configure a default route to 10.1.1.1

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but specify an admin distance of say 100 and that should be the next-hop router of 10.1.1.2 with an admin

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distance of 100.

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So do show IP route

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we've got a route in the routing table

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notice the admin distance is 100 whereas previously

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the admin distances of the routes was 1.

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So 1 shown here the router can ping the loopback of router 5

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and when we trace to the loopback it's going via router 2

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and that should be expected because that's the route that we have in the routing table.

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What happens when we add a static route to router 3 but with an admin distance of 150 and let's add

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router 4 with an admin distance of 200? What do you think the routing table is going to look like?

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So show IP route only shows the route to router 2

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and that's because it's got the lowest administrative distance.

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So when we trace to the loopback of router 5 it's going via router 2 but the running-config shows us that

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there are three routes in the running config.

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So this is a way to implement a preferred path which is router 2 and then a backup path and a second

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backup.

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What will happen now is router 2 will be used as the primary path because that's the only route in the

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routing table

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but, when we shut an interface down, so I'll shut down gigabit 00 the link to router 2 we can see the

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interface has gone down.

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When we type show IP route

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notice the route has changed to go to 10.1.2.2. It has a high administrative distance but that's lower than

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the administrative distance via router 4.

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So now traffic it goes via router 3 again in the running config weve got three routes and this route

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is the route being used at the moment

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because the link to the next-hop router is down because the interface is administratively down.

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So the router can see that this IP address is an interface that's down and that IP address is in the same

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subnet as this IP address.

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So that route is removed from the routing table

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and this route is put in to the routing table.

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So again the static route via 10.1.2.2 is in the routing table.

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Now if we shut gigabit 01 down

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what we should see is that the third route appears in the routing table and it does traffic is now gonna

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go via router 4 what it does it goes to 10.1.3.2 and then on to router 5.

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So again we can still ping the loopback of router 5 but the traffic is taking a different path.

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Notice the administrative distance of this router is 200

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the next hop is 10.1.3.2.

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So if we now no shut gigabit 01

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in other words, enable that interface. What we should see is that the path changes and it has it's now

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going via 10.1.2.2 because that has a low administrative distance.

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And if we no shut gigabit00 

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traffic should switch back to 10.1.1.2 which it has. So administrative distances in this way are often

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used to select a primary path, backup path, and an alternate backup path

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this could be an MPLS link,

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this could be a good internet connection and this could be a not-so-good internet connection.

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So we've got three paths to get to our destination and we'll choose the primary path first

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but if it's not available then this path and if that's not available then we'll choose this path. Now static

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routes don't work that well in that, they will only be removed from the routing table if the local interface

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goes down.

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So as an example if I shut down this link traffic would still go via router 2 and would end up in

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a black hole.

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So as an example, I'll send a thousand pings to router 5 before I start that ping

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I'll get router 2 ready.

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So interface gigabit

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01 notice we are pinging but if I shut that interface down the pings start failing

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we get an unreachable message. Router 1 configured with static routes doesn't realize that there's a problem

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elsewhere in the network.

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So it's still forwarding traffic to 10.1.1.2 even though that link is down. Router 2 in this case

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is running a routing protocol.

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So it can dynamically change its behavior but a router with static routes doesn't do that.

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and that's a reason why you run dynamic routing protocols.

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So when the interface came up again router 1 was able to ping router 5 start that again and shut

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the interface down.

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Now it doesn't dynamically shift traffic to an alternate path.

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So that is a disadvantage of static routes.

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They are static by nature they don't dynamically change based on network conditions.

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They'll only reroute if the local interface goes down.

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But if these interfaces are up the routers unaware of problems elsewhere in the network.

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But if we were running a dynamic routing protocol it would dynamically adjust to network conditions.

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So dynamic routing protocol such as EIGRP, OSPF, and BGP are better than running static routes

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when you want your network to dynamically adjust to network conditions.

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I hope you found this video useful if it was of benefit to you please like it and please subscribe to my

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YouTube channel.

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I wish you all the very best.