What are two purposes of using IPv4 and VPNv4 address-family configurations in a Layer 3 MPLS VPN? (Choose two.)
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A. B. C. D. E.AB.
In a Layer 3 MPLS VPN, the VPN service provider assigns a unique VPN identifier to each customer to isolate their traffic and allow for overlapping IP addresses between customers. The VPN identifier is used to create VPNv4 and IPv4 address-family configurations, which serve two primary purposes:
The first purpose is to ensure that VPN routes are unique within the service provider's network. This is achieved by adding a Route Distinguisher (RD) to the IPv4 route. The RD is a unique identifier assigned to each VPN by the service provider, which ensures that VPN routes are distinguishable from one another. The RD is prepended to the IPv4 prefix to create a VPNv4 address. The VPNv4 address is used to advertise the MPLS VPN label and to route traffic between customer sites.
Option A is incorrect because the RD is not prepended to the IPv4 route. Instead, it is prepended to the IPv4 prefix to create a VPNv4 address.
Option B is correct because the VPNv4 address consists of a 64-bit route distinguisher that is prepended to the IPv4 prefix.
Option D is incorrect because the IPv4 address is not needed to tag the MPLS label. The MPLS label is assigned based on the VPNv4 address.
Option E is correct because the VPNv4 address is used to advertise the MPLS VPN label and to route traffic between customer sites.
The second purpose of using VPNv4 and IPv4 address-family configurations is to allow for overlapping IP addresses between customers. This is achieved by using Multi-Protocol Border Gateway Protocol (MP-BGP) to carry both VPNv4 and IPv4 routes between customer sites. MP-BGP allows the service provider to differentiate between the VPNv4 and IPv4 routes and to maintain separate forwarding tables for each.
Option C is incorrect because MP-BGP is used to carry both VPNv4 and IPv4 routes between customer sites, but it is not used to allow overlapping IPv4 addresses between customers. This is achieved by using the VPN identifier to differentiate between customers.