Layer 3 VPN Static Routing: Advertise Directly Connected Subnets
Question
You have an established Layer 3 VPN where you are using static routing between your PE and CE devices. You must advertise their directly connected subnet to remote PE devices.
Which two methods must you use? (Choose two.)
Answers
Explanations
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A. B. C. D.BC
In a Layer 3 VPN, the Provider Edge (PE) devices are responsible for exchanging routing information with the Customer Edge (CE) devices to provide connectivity between customer sites. When using static routing between the PE and CE devices, it is necessary to advertise the directly connected subnets to remote PE devices.
To accomplish this, there are several methods that can be used, but the question asks for two specific methods. Let's examine each option in detail:
A. Use a site identifier: This method involves adding a site identifier to the route that is advertised from the PE device to the remote PE device. The site identifier is used to distinguish the route from other routes that may be advertised by the same PE device. This method can be useful in multi-site VPNs where each site may have its own unique identifier.
B. Use the VRF table label: This method involves adding a label to the route that is advertised from the PE device to the remote PE device. The label is used to identify the Virtual Routing and Forwarding (VRF) table that the route belongs to. This method is commonly used in MPLS-based VPNs to identify the VPN that the route belongs to.
C. Use a VRF export policy: This method involves configuring an export policy on the PE device to advertise the directly connected subnets to the remote PE device. The export policy specifies which routes should be advertised and how they should be advertised. This method can be useful when more granular control over the advertised routes is needed.
D. Use a route distinguisher: This method involves adding a route distinguisher to the route that is advertised from the PE device to the remote PE device. The route distinguisher is used to distinguish the route from other routes that may be advertised by the same PE device. This method is commonly used in MPLS-based VPNs to distinguish between routes that belong to different customers.
Based on the given options, the two methods that must be used are B. Use the VRF table label and C. Use a VRF export policy. The VRF table label is necessary to identify the VPN that the route belongs to, while the VRF export policy is necessary to actually advertise the directly connected subnets to the remote PE device.
