In an inter-AS L3VPN Option B, the PE-ASBRs use which routing table to store all the VPN routes that needs to be exchanged?
Click on the arrows to vote for the correct answerA. B. C. D.
In an inter-AS L3 VPN Option B, the Provider Edge (PE) routers act as Autonomous System Boundary Routers (ASBRs) and connect to the core Provider (P) routers. The PE-ASBRs exchange VPNv4 routes using Border Gateway Protocol (BGP) with each other, while the P routers only forward these routes based on their MPLS labels.
Option B refers to a scenario where each customer site has its own unique Autonomous System Number (ASN), and the service provider uses AS override to advertise the customer's routes between the PE-ASBRs. In this option, the VPN routes are exchanged between different ASes, and therefore, the PE-ASBRs need to use a separate routing table to store all the VPN routes that need to be exchanged.
The correct answer to the given question is (B) VRF routing table. In an L3 VPN, a Virtual Routing and Forwarding (VRF) instance is used to create a separate routing table for each VPN. Each VPN has its own VRF, which stores the VPN-specific routes learned from the CE routers connected to the PE-ASBRs. The PE-ASBRs use BGP to exchange the VPN routes between the different VRF tables across the different ASes.
Therefore, in an inter-AS L3 VPN Option B, the PE-ASBRs use the VRF routing table to store all the VPN routes that need to be exchanged. The global routing table contains the Internet routes learned from the P routers, while the IGP table contains the intra-AS routing information. The BGP table is used by the PE routers to store the BGP-learned routes, including the VPNv4 routes, but not specifically for storing the VPN routes that need to be exchanged between different ASes.