10.2. Extending IS-IS
New capabilities are added to IS-IS through the addition of new TLVs. This section introduces one such added TLV. Chapters 11 through 13 discuss other TLVs that have been added to IS-IS to support optional capabilities.
10.2.1. The IS-IS Extensibility Advantage
IS-IS tends to be easier to extend than OSPF, and this can be observed historically by the timing of vendors’ rollouts of new features supported by IS-IS and OSPF. Both MPLS TE and IPv6, for example, were supported in IS-IS production implementations six months to one year before they were supported in OSPF.
The reason for this easier extensibility has to do with the fact that new features are introduced by adding new TLVs to an LSP, while the structure of the LSP ...