The ECMP hash algorithm requires the opaque value of the FEC (see Table: Opaque Types) and is based on RFC 6388 section 2.4.1.1.
The following hash is performed: H = (CRC32 (Opaque Value)) modulo N, where N is the number of upstream LSRs. The Opaque Value is the field identified in the FEC element after Opaque Length. The Opaque Length field indicates the size of the opaque value used in this calculation.
The candidate upstream LSRs are numbered from lowest to highest IP addresses. The selected upstream LSR is the LSR that has the value H, as calculated by the hash algorithm.