BIER is only supported on FP4 network interfaces. BIER is not supported on FP3 or earlier cards, or on access interfaces.
If a chassis has a mix of FP3 and FP4 network ports, BIER is signaled on all FP3 and FP4 interfaces that are part of the IS-IS. From a control plane perspective, BIER TLVs are advertised using IS-IS on FP3 and FP4 interfaces. The BIER forwarding table is not downloaded to FP3 cards. Therefore, there is no BIER packet forwarding or processing on these cards. If IGP chooses FP3 L3 interfaces, there are BIER forwarding issues. An event log is generated if an FP3 is part of the BIER sub-domain.
BIER-encapsulated multicast traffic can egress only on FP4 interfaces. Non-FP4 egress interfaces do not forward BIER-encapsulated multicast traffic.