Juniper JNCIA JN0-103 – Routing Fundamentals Part 3

5. Static Routing

Welcome back. In this lecture, we’ll talk about static routing. In the last lecture, we looked at a concept called route preference, and now we’ll move on to discussing static and dynamic routing. And we’ll start off by talking about static routing in this lecture. Let’s begin. What do we mean by static routes? Routes that are permanent fixed in the routing and forwarding tables are often configured as static routes. These routes generally do not change and often include only one or very few paths to the destination. To create a static route in the routing table, you must at a minimum, define the route as static and associate a next top IP address with it. The static route in the routing table is inserted into the forwarding table.

When the next top IP address is reachable, all traffic designed for the static route is transmitted to the configured next top IP address for transit. I have a diagram on the screen to help you understand how can static route help in routing the packets. There are two networks. The one on the left is 192 One and 168 right is 192 168 200:24. Assuming that the device on the left hand side, which is 192 168 110, wants to send a packet to 192 168 210, the device will first start by sending the packet to its default gateway, which is 192 168 one.

The packet has now reached the router, and the router is supposed to forward the packet to the network on the right hand side. This is where routing plays an important role. We must add a route on the router 192 168 one which points to the network on the right hand side. So we would add a route like this for the destination 192 168. Next hop IP address should be the router on the right hand side, which is 192 168 two One.

Similarly, if we wanted to send packets from the network on the right hand side to the network on the left hand side, we would have to configure some routing as well. For example, if 192168 211 wanted to send a packet to 190 to 168 One dot eleven, it will first start by sending the packet to 109 216821, which is the default gateway. Now the packet has reached the router, and the router is supposed to forward the packet to the network on the left. We can accomplish this by adding a static route for the destination 192 168. Next hub IP address of the router on the left, which is 192 168 one One.

That’s how static routing can help us in routing the packets across networks. Let’s now talk about a keyword called no readvrtise. Static routes are eligible to be re advertvisedized. What do we mean by reedvirtized? Well, re advertising means exporting the route from the routing table into other dynamic routing protocols. So static routes are eligible to be re advertised if a policy to do so has been configured to mark an IPV for static route as being ineligible for readvantagement. Include the keyword Nor advertise. It is recommended to use the Nor advertise option on static routes used for management purposes. Management routes are usually not re advertised into other routing protocols, and it’s a good idea to mark them as no re advertise. Let me show you on the terminal how you can mark a route as no re advertise. I’m at the terminal, and I’m first going to enter configuration mode, and I’m going to use the set command. I’ll start with set routing options. Let’s start off with a question mark, and I’m looking for this option over here called static question mark. This option over here called route question mark. I can actually add a static route over here.

For example, if I wanted to do something like this here route 410 10 slash 24, question mark. And here I have the option to specify the Next Top IP address, which is over here. So I could do next top and then the next top IP address. But right now, that’s not what we are trying we are trying to understand the no resolve keyword. And for that, I’m going to use an existing route, which is over here, zero zero, our default route. So let me erase this from here. Do a question mark. We have the existing route, all right? And now when I do a question mark, you’ll see over here, we have the option to re advertise the route, or we have the option to set no readvertise, so we can do no readvantage. So that’s how we prevent a route from being re advertised into other routing protocols. Let’s now talk about resolve. By default, the Juno’s operating system requires that the Next Top IP address of static routes be reachable using a direct route. By now, we know that when we configure a static route destination, we also configure a Next Top IP address.

All packets for that destination are forwarded to that Next Top IP address. Now, this statement says that Juno’s requires that the next top IP address of the static route should be reachable using a direct route. Unlike software from other vendors, the Juno’s operating system does not perform recursive lookups of Next hops by default. I know this might sound confusing. I have an example coming up right away. However, this behavior can be changed by using the keyword called resolve. In addition to using the resolve keyword, a route to the indirect Next Top is also required. I know this could have confused you. Let me show you a diagram.

So, we have three routers on the screen right now. Router A on the left, router B in the center, and Router C on the right hand side. Router A has an IP address of 198 168 one one. Router C has an IP address of 192 168, one six. And it is also connected to a network which is 109 2168-2024. Imagine this. If Router A wanted to send a packet to 192 168 next hop IP address would be 192 168 one six. Because Routerc knows how to forward the packet to that network, it makes sense to give the next top IP address as the IP address of Routerc. So for Router A, the next top IP address risk to reach 192 168 200:24 is 192 168 one six.

However, there’s a problem. The IP address 109 216816 is not directly reachable from Router A. It’s an indirect Next hop IP address because there’s another router in between. In such situations where the next hop IP address is not directly reachable, we have to use the keyword called resolve. In addition to that, Juno’s must also have a route to reach the next half IP address. Which means in this case, we must have a route available to reach 192 168 one six as well. So there are two items that we need to satisfy. Number one, we need to use the keyword called resolve.

Why? Because 192 168 200:24 has a Next hub IP address of 192-1681 dot six, which is not directly reachable. If it’s not directly reachable, or in other words, if it’s a indirect Next hop, we have to use the keyword called resolve. Additionally, there must be a route available to reach 192 168 one six, the indirect NextTop. So in configuration, this is how it will look like. We are under Edit routing options and we have done a show command. We can see that we have a route pointing to 198 168 Next top IP address of 198-21-6816. We additionally need to use the keyword called resolve, which will make the configuration look like this, right? So it’s just a simple keyword called resolve to make this work. Now, let’s talk about qualified NextTop. A static route destination address can have multiple Next tops associated with it. In this case, multiple routes are inserted into the routing table and route selection must occur. What this means is when we are configuring a static route for a specific destination, it is not necessary that we have only one Next top IP address. We could have multiple Next top IP addresses. In such cases, we need to select one.

Let me show you an example. In this diagram, we have a network on the left hand side which is 192 168 is connected to a router. The router has two IP addresses 192 168 one One and 192 168 one 5192 168 one one uses the next top IP address of 192 160 at one dot two to reach the Internet, while 192-1681 dot five uses the next top IP address of 192-1681 dot six to reach the Internet. As you can see, the ultimate destination is to reach the Internet. And we have two possible next top IP addresses one two and one six. In this case, we must select one of the two routes. How do we make this happen? The answer is qualified. Next top. Let me show you how. So, the primary criterion for route selection is route preference. We spoke about route preference in the last lecture. Route preference is what makes a route more or less desirable. It is possible to influence the primary route selection by setting the route preference associated with a particular Next Hub IP address. We learned that routes with a lower route preference value are always used to route traffic.

When we do not set a preferred route, the Juno’s operating system chooses, in a random fashion, one of the Next Top IP addresses to install into the forwarding table. In general, the default properties assigned to a static route apply to all the Next Top IP addresses configured for the static route. We know that static routes have a default preference value of five. In this case, both the Next Top IP addresses have been statically configured, which means both of them have the default preference value of five. If we want to configure two possible Next Top IP addresses for a particular route and have them treated differently, we can define one of them as a Qualified Next Hop.

Qualified Next Hops allow you to associate one or more properties with a particular Next Top IP address. Which means if we want one of the two routes to have a different preference value, we can use Qualified Next Hub. We can set an overall preference value for a particular static route and then specify a different preference value for the Qualified Next Top. Let me show you how we have the same diagram on the screen. The configuration would look like this. The default route is pointing to zero. The next top IP address has been specified as 192 168. One, two The Qualified next top IP address has been set as 192 168. One six. And notice that the Qualified Next Top has a preference value of seven. We know that static routes have a default preference value of five.

In this case, the Next tab IP address of 192 168 One Two, will carry the default preference value of five. And the Qualified Next tab, which is 192 168 One six, will carry a preference value of seven. Since the first one is lower, juno’s will automatically use that as the preferred Next Top IP address. As you can see, with this concept of Qualified Next Top, we can influence the route selection process. Isn’t that really cool? We can actually play a role in how Juno selects a route for forwarding traffic.

Let me show this to you on the terminal. I’m back over here. I’m first going to erase this command, and I’m going to start with set routing options. Let’s do a question mark and let’s do static route. Let’s do a question mark. Over here, we have only one configured static route, so we’ll have to use that. And I’m going to do a question mark. You can see that we have the option to specify the qualified Next Top IP address over here, so we can do qualified Next Top IP address, question mark here.

We can put the next top IP address, and we can specify the preference value. All right, so that’s all for this lecture. In the next lecture, we’ll talk about some really interesting concepts on dynamic routing. I’d like to thank you for watching, and I’ll catch you in the next lecture. Thank you.

6. Dynamic Routing

Welcome back. In this video, we’ll talk about dynamic routing. We’ll understand some of the differences between static routing and dynamic routing, and we’ll understand the different types of dynamic routing protocols. Let’s begin. All right, let’s talk about some of the concepts of dynamic routing. Static routing works well for smaller networks works, or when you need tight control over routing on large networks, static routing is hard to manage. There’s a lot of routes that you’ll have to configure. There’s chances of configuration mistakes and routing going wrong. For large networks or networks that change frequently, dynamic routing is a better choice. With dynamic routing, you configure the network interfaces to participate in a routing protocol. Devices running the dynamic routing protocol can dynamically learn routing information from each other.

When a device adds or removes routing information for a participating device, other devices automatically update. What are the advantages of dynamic routing? The first one is the most significant one. It is very easy to configure. Devices learn routing information automatically, eliminating the need for manual routing entries. Number two increased network availability. When routes change or fail, dynamic routing reroutes the traffic automatically with static routing. If a route actually fails, we have to make the changes manually. So that is another significant benefit. Number three better network scalability. When the network grows, new routes can be easily learned. Let’s talk about the different types of dynamic routing protocols. But before we talk about that, we need to understand what do we mean by autonomous system? An autonomous system is a collection of routers under a common administrative domain, also referred to as a routing domain.

Typically, an autonomous system represents a collection of devices under the same organization or managed by the same organization. It is also known as a routing domain. Routing protocols used for routing between autonomous systems, also known as inter autonomous system routing, are referred to as exterior gateway protocols or EGPS. The example of EGP is the most common protocol on the Internet. In fact, it is the only EGP used on the Internet border gateway protocol or BGP. On the other hand, routing protocols used for routing inside an autonomous system, also known as intra autonomous system routing, are referred to as interior gateway protocols or IGPs. We have a few examples for IGPs, for example, routing information protocol or rip, open shore dispatch first protocol, OSPF, interior gateway routing protocol, iGRP, and so on. Interior gateway protocols can be further classified as distance, vector, or link state routing protocols. Both of them are still interior gateway protocols, which means they are used for intra autonomous system routing, but they are different in the way they function. Let’s take a look at that.

All right, so before I talk about interior gateway protocols in detail, here is a diagram to help you visualize what is the difference between an exterior gateway protocol and an interior gateway protocol. I have one organization on the left and one organization on the right. As we just understood. A collection of devices under a common administrative domain is referred to as an autonomous system.

So Organization One has the autonomous system number 100 and Organization Two has the autonomous system number 200. The routing protocol that is used for routing within Organization One or within Organization Two is referred to as interior interior gateway protocol, while the routing protocol which is used to connect between the organization on the left and the Internet, and the organization on the right and the internet. So which means we are trying to route between the autonomous systems. We use exterior gateway protocols, for example BGP or border gateway protocol. All right, now let’s talk about distance vector routing protocols. Routers that share a link and configured to use the same routing protocol are called as neighbors. So if we have two routers, they share a common link and let’s say they both are running rip or routing information protocol. In this case, both. The routers will be called as neighbors with distance vector routing protocols. Routing updates are shared with neighbors. That means if one router has to share the information or a routing update, it will be shared with its neighbors only.

Routing updates are periodic, which means when a certain amount of time elapses, the routing updates are sent out. The router only knows about its own interfaces in the remote network that can be reached through its neighbors. In other words, the router is not aware of the network topology. Let’s now compare this with link state routing protocols, also known as shortest path first protocols. Link state routing protocols compute the best path to reach each destination. Routing updates are shared with all the routers, and this is a significant difference with distance vector routing protocols. Routing updates are only shared with the neighbors and we know what a neighbor means, right? Routers that share a common link and running the same protocol are termed as neighbors with link state routing protocol. The routing updates are shared with all routers inside the autonomous system.

Routing updates are sent only when there is a change on the network and only the changes are sent, not the entire routing table. This is another significant difference with distance vector routing protocol. Routing updates are periodic, which means after a certain amount of time, routing updates are definitely sent out. Over here, routing updates are sent only when there is a change in the network, which is definitely more efficient than distance vector routing protocols. Routers have complete view of the network topology with distance vector routing protocol, routers only know about the neighbors, not the entire topology. Convergence time is less compared to distance vector routing protocols. In simple words, convergence time means how quickly the routers exchange the information and get ready for routing the packets. So that’s all about dynamic routing protocols. From the examination standpoint, we are not required to know how to configure dynamic routing protocols. We just need to know the benefits of dynamic routing protocols. In the next lecture, we’ll talk about OSPF. I’d like to thank you for watching, and I’ll catch you in the next lecture. Thank you.