The Inter-AS MVPN feature allows set-up of Multicast Distribution Trees (MDTs) that span multiple Autonomous Systems (ASes).This section focuses on multicast aspects of the Inter-AS MVPN solution.
To support Inter-AS option for MVPNs, a mechanism is required that allows setup of Inter-AS multicast tree across multiple ASes. Because of limited routing information across AS domains, it is not possible to setup the tree directly to the source PE. Inter-AS VPN Option A does not require anything specific to inter-AS support as customer instances terminate on ASBR and each customer instance is handed over to the other AS domain via a unique instance. This approach allows operators to provide full isolation of ASes, but the solution is the least scalable case, as customer instances across the network have to exist on ASBR.
Inter-AS MVPN Option B allows operators to improve upon the Option A scalability while still maintaining AS isolation, while Inter-AS MVPN Option C further improves Inter-AS scale solution but requires exchange of Inter-AS routing information and therefore is typically deployed when a common management exists across all ASes involved in the Inter-AS MVPN. The following sub-sections provide further details on Inter-AS Option B and Option C functionality.