In TUC IP MPLS project, the IS-IS (Integrated Intermediate System – Intermediate System) chosen as IGP routing protocol for both aggregation and access layers.
As shown below, considering those ANs’ routing capacity and access layer’s expandability, each access layer(from AN to PN) will running a separate ISIS process; as the conjunction, the PNs have to running multiple IS-IS processes, one for the aggregation layer, another for mounted access layer.