Configure And Verify VRF Lite

Exam: Cisco 200-301 - Cisco Certified Network Associate (CCNA)

We in this chapter will take up the topic of “configure and verify VRF lite”. This is a topic that you will find under the exam number 300-101 route. It appears under the main topic of layer three technologies. It is a closed book exam and the questions are objective type this is why it is essential that you prepare the topic well and prepare it from the exam point of view.

Let us first understand what VRF lite is. Well it is nothing but the extension of IP routing and provides a number of routing instances.VRF lite is the short form of “VPN routing and forwarding lite” for the ML- series cards. It is made in such a way that it will provide a separate IP routing and forwarding table for each of the VPN.

It is used along with the multi protocol internal BGP (MP-IBGP). In a ML series the VRF implementation is without the MP-IBGP. If the ML series comes with a VRF lite it will be considered as a PE-extension or a customer equipment extension. The CE extension can have multiple VRFs and can serve a number of customers with just one CE box.

You will also at times notice that VRF lite on a ML series CE can have a number of subinterfaces and interfaces with the PE for different customers. However, a normal CE will have only one customer. The routing information of the VRF is considered locally and it will not distribute the VRF to the connected PE. Sometimes it will also use the VRF information for directing the traffic to the correct subinterface or interface. This happens when the traffic is received from the customers or from an internet service provider.

The interfaces in a VRF can be both physical and logical. The physical interfaces are Ethernet ports. The logical interfaces are SVIs and VLANs. In case of layer three technologies you must remember that it cannot belong to more than one VRF at a given time. VRF lite can support the cat 4500. However, it does not include the provider edge MPLS functionality. It will also not include MPLS control plane and MPLS label switching. These are not supported in the VRF lite implementation. You must keep these points in mind as a network administrator. The VRF lite interfaces always need a layer three interface. Some of the points that you must keep in mind as you configure the VRF lite are:

A switch that has VRF lite will be shared by a number of customers. Each of these customers will have their own routing tables.
The VRF lite will allow multiple customers to use the VRF tables as a result the same IP address can be used again. Overlapped IP addresses are also allowed at times in different VPNs.
The VRF lite will also not support the ISIS and IGRP.
If you want to configure a multicast on the same layer 3 interface at the same time it may not be possible.
The VRF lite will also not affect the packet switching rate.
The customer can use multiple VLANs but the VLAN should not overlap with the VLAN of the other customers.

Now that you have got a good idea of what the VRF lite actually is we will now move on to discuss how you can configure the same. The steps that you will have to follow are as mentioned below:

First you will have to enter the VRF configuration mode and then assign the VRF name.
As a second step create a VPN route distinguisher with the help of the command – router (config-vrf) #rd router-distinguisher. The RD will help you to create forwarding and routing table. It will also specify the default route distinguisher for the VPN that is in use. The RD will always be added to as a prefix to the customers IPv4. The RD can be a 32 bit number or a 16 bit number.
As the third step you will have to create a list of export and import route target communities for the specified VRF.
The fourth step is an optional one. In this you are needed to associate the specified route map with the VRF.
In the fifth step you are required to exit the configuration mode you are in and enter the global configuration mode.
As a sixth step you will have to specify the interface and enter the interface configuration mode.
In this stage you are needed to associate the VRF with the subinterface or the interface.
In this step you will have to leave the privileged EXEC mode by using the command router (config- if) # end.
The last step that we are about to discuss is considered optional. What you are required to do in this is save the changes that you have made in the configuration to NVRAM.

We will now discuss how to monitor and verify the VRF lite. We will basically give a list of some commands that you can use in order to monitor and verify the VRF lite that you have configured using the above steps that we have discussed:

If you want to display the IP routing table for a VRF the command that you will need to use is router # show ip route vrf vrf –name.
If you want to the set of the interfaces and VRFs then you will have to use the command router# show ip vrf.
If you want to display the routing protocol information for the VRF the command that you will need to use is router # show ip protocols vrf vrf name.
If you want to ping an ip address that has a specific VRF the command that you will need to use is router # ping vrf ( vrf name ) ip ip address.

The topic is vast but these are all that you need to know from the CCNP exam point of view these are the points that you must know well and also try to prepare for the exam on these lines. It will help you to get a better score and do well in the exam.

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