300-440 Question 164
Select 3A service provider is implementing an MPLS Layer 3 VPN for a customer with multiple sites. The customer requires routing information to remain isolated between their VPN and other customers' VPNs. Which two mechanisms are used in MPLS Layer 3 VPNs to ensure this isolation and proper routing?
- A
Multiprotocol BGP (MP-BGP) to exchange VPN routing information
- B
Route Distinguisher (RD) to uniquely identify overlapping routes in different VPNs
- C
Label Distribution Protocol (LDP) to direct VPN traffic to the correct site
- D
Route Target (RT) to control route import/export between VRFs
- E
Interior Gateway Protocol (IGP) to propagate VPN routes within the MPLS network
Show answer and explanation
Correct answers: A, B, D
Explanation
MPLS Layer 3 VPNs rely on MP-BGP for advertising VPN-specific routes, RDs for ensuring unique identification of overlapping routes, and RTs for controlling import/export of routes between VRFs. These mechanisms collectively ensure routing isolation and correct traffic forwarding for multiple customer VPNs. LDP and IGPs are used in different contexts within the MPLS network but are not directly responsible for VPN route isolation.
- A. Correct.
Correct. MP-BGP is the protocol used to distribute VPNv4 or VPNv6 routing information between PE routers while keeping VPNs isolated.
- B. Correct.
Correct. RDs allow overlapping IP addresses in different VPNs to be uniquely identified, ensuring routing table isolation.
- C. Incorrect.
Incorrect. LDP is used for label distribution but does not directly handle VPN traffic isolation or routing information exchange.
- D. Correct.
Correct. RTs are used to control which routes are imported/exported between VRFs, enabling route segregation and policy enforcement.
- E. Incorrect.
Incorrect. IGPs like OSPF or EIGRP are not used for propagating VPN-specific routes; MP-BGP handles this function in MPLS Layer 3 VPNs.