Understanding Inter-AS MPLS L3VPN Option C
????MPLS L3VPN provides Layer 3 VPN services over an MPLS backboneby using BGP to exchange VPN routes.
????Inter-AS MPLS L3VPN Option C (Carrier-to-Carrier Model) works as follows:
ASBRs (Autonomous System Boundary Routers) exchangeVPNv4 routes using MP-BGP.
ASBRsdo NOT store VPN routing tables. Instead, theyadvertise labeled IPv4 routesto enable inter-AS forwarding.
How ASBR-PE2 Enables Inter-AS Communication?
✅VPNv4 Address Family (Answer A - Required)
Used to exchangeMPLS VPN routes between PE routers.
MP-BGP (Multiprotocol BGP) exchanges VPNv4 prefixesbetween ASBR-PE1 and ASBR-PE2.
✅Unicast BGP Address Family (Answer D - Required)
Required to exchangeIPv4 labeled routesbetween ASBRs.
EnsuresMPLS label forwarding between AS100 and AS200.
❌BGP-LS Address Family (Answer B - Not Required)
BGP-LS (BGP Link-State) is used for SDN controllersto learn topology information.
It isnot required for Inter-AS MPLS L3VPN.
❌VPN Instance Unicast Address Family (Answer C - Not Required)
This is used forPE-CE communicationbut isnot 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 incarrier-to-carrier MPLS VPN deployments.
Enterprise WAN Interconnection:Enablesmulti-AS MPLS VPN connectivityfor large enterprises.
✅Reference:Huawei HCIE-Datacom Guide – Inter-AS MPLS L3VPN Option C (Carrier-to-Carrier Model)
