IS-IS supports multiple levels and BIER is supported under each level using the following rules:
If the ABR is not a BFIR or BFER, the BIER sub-TLV must be leaked between different levels (areas) at the ABR. A BIER template without a BFR ID must be on both levels.
The ABR can support BFIR and BFER functionality. ABR does not support BIER header stitching.
A single area can have level 1 and level 2. In this case, the same template can be programmed on both levels.