After IGP TE is configured on all LSRs in an MPLS domain, a TEDB is generated on each LSR.
Either OSPF TE or IS-IS TE can be used:
If neither OSPF TE nor IS-IS TE is configured, LSRs generate no TE link state advertisement (LSA) or TE Link State PDUs (LSPs) and construct no TEDBs.
TE tunnels cannot be used in inter-area scenarios. In an inter-area scenario, an explicit path can be configured, and the inbound and outbound interfaces of the explicit path must be specified, preventing a failure to establish a TE tunnel.
OSPF TE uses Opaque Type 10 LSAs to carry TE attributes. The OSPF Opaque capability must be enabled on each LSR. In addition, TE LSAs are generated only when at least one OSPF neighbor is in the Full state.
IS-IS TE uses the sub-time-length-value (sub-TLV) in the IS-reachable TLV (22) to carry TE attributes. The IS-IS wide metric attribute must be configured. Its value can be narrow, wide, compatible, or wide-compatible.