How have Traffic Engineering extensions to IS-IS been implemented?

IS-IS is an extensible protocol that uses Type-Length-Value (TLV) structures to carry information within its Link State PDUs (LSPs). To support Traffic Engineering (TE), new TLVs were defined to advertise additional link attributes not used by the standard SPF calculation. These attributes include maximum link bandwidth, reservable bandwidth, administrative group (color), and TE default metric. This information is then flooded throughout the IS-IS domain and used by algorithms like CSPF to compute constrained paths for TE LSPs.

A. LSAs (Link State Advertisements) are a construct of the OSPF protocol, not IS-IS. IS-IS uses Link State PDUs (LSPs) which contain TLVs.
B. OSPF opaque LSAs are specific to OSPF-TE. IS-IS uses its own mechanism (TLVs) and does not rely on OSPF constructs for its TE extensions.
D. CSPF is the algorithm that uses the TE information distributed by the protocol extensions; it is not the implementation of the extensions themselves.

1. IETF RFC 5305, "IS-IS Extensions for Traffic Engineering", Abstract. "This document describes extensions to the IS-IS protocol to support Traffic Engineering (TE). This is done by adding new information to the IS-IS Link State PDU (LSP). The new information is encoded in Type-Length-Value (TLV) triplets."

2. Nokia 4A0-103 Multiprotocol Label Switching Student Guide, Module 5: Traffic Engineering. The guide explains that IS-IS and OSPF were extended to carry TE link parameters, specifying that IS-IS uses new TLVs for this purpose.