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Free CCNA | VRF | Day 54 (part 3) | CCNA 200-301 Complete Course — Transcript · YTtoTranscript

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Free CCNA | VRF | Day 54 (part 3) | CCNA 200-301 Complete Course

Jeremy's IT Lab · 2,392 words · 12 min read · EN-ORIG

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Below is the complete, readable transcript of Free CCNA | VRF | Day 54 (part 3) | CCNA 200-301 Complete Course by Jeremy's IT Lab on YouTube. Read the full text, copy any part you need, or generate a transcript for any video with our free tool.

Welcome to Jeremy's IT Lab. This is a complete course for the CCNA. In this video, we will cover virtual routing and forwarding, VRF. VRF allows us to divide one physical router into multiple virtual routers. You can think of it like VLANs for routers. VLANs divide a switch into multiple virtual switches, each with their own

broadcast domain. And VRF divides a router into multiple virtual routers, each with their own routing table. Here's what we'll cover in this video. First, I will introduce the concept of VRF and its capabilities. And then introduce VRF configuration. Note that VRF configuration isn't actually a CCNA exam topic. But I think seeing the configurations will help you

understand how it works. Unfortunately, VRF isn't supported in Packet Tracer. So, if you want to try it in a lab, you'll need to use something like Cisco Modeling Labs, CML. Or real Cisco devices. Let's get started. The diagram at the bottom gives an idea of how VRFs work. The black box in the middle represents

R1, a single physical router. The blue, green, and red router icons inside represent three virtual routers inside R1, three VRFs. Let's call them VRF1, VRF2, and VRF3. So, virtual routing and forwarding is used to divide a single router into multiple virtual routers. This is similar to how VLANs are used to divide a single switch, a LAN, into

multiple virtual switches, virtual LANs. By default, all interfaces on a switch are in the same LAN, the same broadcast domain. When using VLANs, we can divide that one broadcast domain into multiple virtual broadcast domains. Similarly, by default, all router interfaces are all in the same routing domain. By routing domain, I mean by default

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traffic received on one router interface can be forwarded out of any other interface on the router if the routing table says to do so. For example, without using VRF, in the diagram below, traffic received on R1's G0/0 interface can be routed to and forwarded out of R1's G1/2 interface. However, with VRF, that won't be

possible. G0/0 is in VRF 1 and G1/2 is in VRF 3. So, traffic cannot be forwarded between them. How does VRF accomplish this? It does this by allowing a router to build separate routing tables. Normally, a router has one routing table, but with VRF, it has multiple. Interfaces, specifically layer 3 interfaces, are configured to be in a

specific VRF, also known as a VRF instance. Keep in mind that VRF does not apply to layer 2 interfaces on a switch. Only router interfaces, SVIs, and routed ports on multi-layer switches can be configured in a VRF. It's a layer 3 concept. As I mentioned before, traffic in one VRF cannot be forwarded out of an

interface in another VRF. However, as an exception, VRF leaking can be configured to allow traffic to pass between VRFs. That is a more advanced concept, though, and I won't cover it in this video. So, what is the main purpose of VRF? Well, VRF is commonly used to facilitate MPLS, Multi-Protocol Label Switching. However, that's actually not the kind of

VRF we are talking about here. The kind of VRF we are talking about is VRF light, VRF without MPLS. So, keep in mind that when I say VRF in this video, I'm really referring to VRF light. VRF is commonly used by service providers to allow one device to carry traffic from multiple customers.

How does it help with that? Well, there are two main points. First, each customer's traffic is isolated from the others because each customer connects to their own virtual router within the service provider's physical router. In the diagram below, let's say the blue, green, and red devices represent three different customers. All customers connect to the same

service provider router, R1, but each connects to a different virtual router, a different VRF instance. And another major point is that customer IP addresses can overlap without issues. For example, the blue customer uses subnets 192.168.1.0/24 and 192.168.2.0/24. The green customer also uses 192.168.1.0/24 and 2.0/24. And so does the red customer. Without VRF, this kind of configuration

is not possible on a router. But with VRF, it works fine even though the IP addresses all overlap. Okay, now let's try configuring VRF to help understand how it works. To demonstrate VRF configuration, I'll use the network below. SPR1 is a service provider router providing WAN services to two customers, customer one and customer two.

C1R1 and C1R2 belong to customer one and C2R1 and C2R2 belong to customer two. Note the subnets being used. Both customer one and customer two use subnet 192.168.1.0/30. First, let's see what happens when we try to configure this without using VRF. First, I configured SPR1's G0/0 and G0/1, both connected to customer one's

routers. No problems yet. But when I try to configure G0/2, I get an error message. 192.168.1.0 overlaps with G0/0. G0/2 cannot use IP address 192.168.1.1 because it is in the same subnet as G0/0. In this case, it's the exact same IP address. But even if the IP address is different, it won't work. Let me

demonstrate that. To prove that point, I tried to configure it as 192.168.1.2, but again, it didn't work. Even if the IP address is different, G0/2 cannot be configured in the same subnet as G0/0. So, without the use of VRF, two interfaces on the same router cannot be in the same subnet. Next, let's use VRF to configure this

network properly. First, we have to create the VRFs, which can be done in global config mode with the command IP VRF followed by the VRF name. Here, I created two VRFs, one named customer one and the other customer two. I then used the command show IP VRF, which shows all of the VRFs on the

router. As you can see, the customer one and customer two VRFs were created. The next step is to assign interfaces to each VRF. So, from interface config mode for G0/0, I used the command IP VRF forwarding customer one. G00 is now part of the customer one VRF. However, I also got this message.

Interface G00 IPv4 disabled and addresses removed due to enabling VRF customer one. If an interface has an IP address configured, the IP address will be removed when you assign the interface to a VRF. So, I then reconfigured the IP address 192.168.1.1/30. I then configured G01. Again, the IP address I configured before was removed

when I assigned it to the VRF. So, I had to reconfigure it. I then configured the G02 interface. Note that this time it worked. I was able to configure G02 as 192.168.1.1/30 even though it overlaps with G00. That's because they are in separate VRFs. I then configured G03 as well. I then once again confirmed the VRFs and

now you can see the interfaces listed in the output. So, SPR1 is now divided into two separate virtual routers. The customer one VRF, which includes G00 and G01, and the customer two VRF, which includes G02 and G03. So, basic configuration of VRF light is simple. Create VRFs with the IP VRF command and then assign interfaces to

VRFs with the IP VRF forwarding command. There is, of course, a lot more depth to VRFs, but that's all we'll look at for now. I then used show IP route on SPR1, but I don't see any routes. Usually, you'd expect to see connected and local routes after configuring IP addresses on interfaces. So, why is

nothing displayed here? Show IP route displays the global routing table. That's the normal routing table you're used to when not using VRFs. In this case, all of SPR1's interfaces are configured in VRFs, so nothing displays here. By the way, you can have a mix of interfaces using and not using VRFs. So, I then use the command show IP route

VRF customer one. And now we can see some routes. Connected and local routes for G00 and G01. So, if you want to see a VRF's routing table, you have to add VRF and the VRF's name to the end of the command. Here I viewed the customer two VRF's routing table. So, these are separate routing tables

from each other and from the global routing table. By the way, if an interface is not in a VRF, its routes will appear in the global routing table. And it will be isolated from the interfaces in VRFs, just like interfaces in different VRFs are isolated from each other. To test reachability, I tried some pings

from SPR1. I first pinged 192.168.1.2, but all the pings failed. Why is that? It's because in the global routing table, there are no routes. As I showed in the previous slide, the global routing table is empty. You can specify the VRF when pinging like this. Ping VRF, the VRF name, and then the

destination. This time the pings worked. Which device was SPR1 pinging in this case? There are two devices with the IP address 192.168.1.2, C1R1 and C2R1. But in this case, SPR1 was pinging C1R1 because I specified the customer one VRF. In the customer one VRF again, I pinged 192.168.11.2, C1R2, which worked. And then

192.168.12.2, C2R2, which didn't work. That's because in the customer one VRF's routing table, there is no route to the destination .12.2. This time I pinged 192.168.1.2 and specified the customer two VRF. Who is SPR1 pinging this time? C2R1, connected to G02 in the customer two VRF. And I pinged 192.168.12.2, C2R2, which worked this time because I

pinged in the proper VRF. So, to sum it up, hosts in the same VRF can communicate with each other. And hosts in different VRFs can't. SPR1 was divided into two separate virtual routers. Here's what we covered in this video. I introduced VRFs and showed the basics of how they are configured in Cisco IOS.

But remember, what we mentioned in this video is more accurately called VRF light, which means we're not using VRF with MPLS. VRF is used to split a router up into multiple virtual routers, each with their own routing table. Service providers can use VRFs to allow multiple customers to connect to the same infrastructure while still allowing

their traffic to be isolated. Plus, it doesn't matter if customers use the same IP addresses in their networks because each VRF is a separate routing table. For the CCNA, it's enough to just understand the basic purpose of VRF. But if you go further to study at the CCNP level and beyond, you'll definitely

have to study VRF in more depth. Okay, let's go to the quiz. Here's question one. You issue the following commands on R1's G00 interface. However, after issuing show IP interface brief, you notice that G00 does not have an IP address. Why is that? Pause the video now to think about the answer. Okay, the answer is B. The IP address

was removed by the IP VRF forwarding VRF 1 command. As I showed earlier, if an interface already has an IP address, that IP address will be removed when you assign it to a VRF. You will then have to reconfigure the IP address. So, if you're planning to use VRFs, you should configure the interface IP

addresses after assigning them to VRFs. Okay, let's go to question two. Examine the network below. If you issue the command ping 192.168.1.10 on R1, which device will respond? Pause the video now to select the best answer. Okay, the answer is D. No device will respond. Actually, R1 won't be able to even send

the pings. All of R1's interfaces are assigned to VRFs, and a ping without specifying a VRF will use the global routing table. None of R1's interfaces are using the global routing instance, so the routing table will be empty, and it won't be able to send the pings. Okay, let's go to question three.

Which of the following statements about VLANs and VRFs are true? Select three. Pause the video now to select your answers. Okay, the answers are C, D, and F. VRFs divide routers up by creating separate routing tables. In effect, you are dividing the router into separate virtual routers. VLANs, on the other hand, divide

switches up by creating separate broadcast domains. And router interfaces in different VRFs can have the same IP address, as I demonstrated in this video. A is incorrect because VRFs do not create separate broadcast domains. Router interfaces are already in separate broadcast domains anyway, without VRFs. B is wrong because VLANs do not create

separate MAC address tables. Even when using VLANs, the switch still keeps one MAC address table. And E is wrong because VRFs can also be configured on the SVIs and routed ports of multilayer switches, not just on routers. Okay, that's all for the quiz and this video. I hope it was helpful. Thanks for

watching. Before finishing this video, let me thank my JNCIP level channel members. To become a member, please click the join button under the video. Thanks to Yonatan Macara, Velva Jacob, George Streeter, Funny Dart, Naseer Choudhury, Devin Suku, Gustavo Biar, Gerard Baker, Marcel Lord, Pavel M, Mr. Earlesson, Dragos Hirnea, Zaki Shah, Mer Salmon, Mazen Anderson, Vytautas 194,

Gino Lindley, Nehemia, Justin Watky, Mark Jackson, Bold 1C1U, Michael Carroll, Gerald Guian, Gabriel Braga, Renan Morais, Hector Hernandez, Ali Polat, Maratuba, Roji Kuriakose, Arpad Konives, 5 Feet, Daniel Brown, Tricky Micky 123456, Scott Thompson, Jose Alvarez, Kevin Hayes, Hussein Yavuz, Samuel Tavares, Mustafa Ersoy, Dear Diso, Nasser Zahar, Alexandru Badici, Brian Grant, Georgi Gemidjev, Ahmed Ismail, Dibya Swain, Tan

No, Arlin Plgaria, Adilson Pereira, Abdo Zizo, and Farhad 69. Sorry if I pronounced your name incorrectly, but thank you so much for your support. Thanks to you and my other supporters, I am able to make these videos and release them for free on YouTube. So, I really appreciate the support. Another great way to support the channel

is to like the video, leave a comment, subscribe, and most importantly, share this video with others. So, if this video was helpful, I'd appreciate it if you did any of those. Thanks for watching.