Understanding Inter-AS MPLS L3VPN Option C
# MPLS L3VPN provides Layer 3 VPN services over an MPLS backbone by using BGP to exchange VPN routes.# Inter-AS MPLS L3VPN Option C (Carrier-to-Carrier Model) works as follows:
* ASBRs (Autonomous System Boundary Routers) exchange VPNv4 routes using MP-BGP.
* ASBRs do NOT store VPN routing tables. Instead, they advertise labeled IPv4 routes to enable inter-AS forwarding.
How ASBR-PE2 Enables Inter-AS Communication?
# VPNv4 Address Family (Answer A - Required)
* Used to exchange MPLS VPN routes between PE routers.
* MP-BGP (Multiprotocol BGP) exchanges VPNv4 prefixes between ASBR-PE1 and ASBR-PE2.
# Unicast BGP Address Family (Answer D - Required)
* Required to exchange IPv4 labeled routes between ASBRs.
* Ensures MPLS label forwarding between AS100 and AS200.
# BGP-LS Address Family (Answer B - Not Required)
* BGP-LS (BGP Link-State) is used for SDN controllers to learn topology information.
* It is not required for Inter-AS MPLS L3VPN.
# VPN Instance Unicast Address Family (Answer C - Not Required)
* This is used for PE-CE communication but is not required between ASBRs.
Why is the Answer A, D?
# VPNv4 routes enable inter-AS VPN communication.# IPv4 unicast routes are required for ASBR-PE2 to forward packets across AS boundaries.
Real-World Application:
* Service Provider Networks: Used in carrier-to-carrier MPLS VPN deployments.
* Enterprise WAN Interconnection: Enables multi-AS MPLS VPN connectivity for large enterprises.
# Reference: Huawei HCIE-Datacom Guide - Inter-AS MPLS L3VPN Option C (Carrier-to-Carrier Model)