Method and apparatus for exchanging routing information and the establishment of connectivity across multiple network areas

Abstract

Routes may be installed across multiple link state protocol controlled Ethernet network areas by causing ABBs to leak I-SID information advertised by BEBs a L1 network area into an L2 network area. ABBs will only leak I-SIDs for BEBs where it is the closest ABB for that BEB. Where another ABB on the L2 network also leaks the same I-SID into the L2 network area from another L1 network area, the I-SID is of multi-area interest. ABBs will advertise I-SIDs that are common to the L1 and L2 networks back into their respective L1 network. Within each L1 and L2 network area, forwarding state will be installed between network elements advertising common interest in an ISID, so that multi-area paths may be created to span the L1/L2/L1 network areas. ABBs may summarize BEB multicast trees such that the set of trees for a given I-SID transiting the ABB is condensed into a common tree. The L2 network may further be implemented as a second layer implemented using a L1/L2/L1 network structure, so that the L1/L2/L1 network structure may recurse an arbitrary number of times.