IS-IS is based on the OSI model and assigns IS-IS nework router addresses to facilitate routing, bandwidth scalability and convergence. Routers build link state packets (LSP) based on local IS-IS interfaces and adjacent router prefixes. The routers flood LSPs to adjacent routers, and packets are encapsulated in the data link layer. IS-IS then adapts to Internet Protocol data transfer.
Key IS-IS features include:
Flexible timer tuning
Rapid LSP data flooding
IS-IS routing components include a routing database that holds link state and forwarding databases, as well as the following four processes:
Receive: Includes data entry point (user/routing data, error reports, control packets), forwarding process user data, and error reports and update process routing data and control packets.
Update: Generates local LSPs flooded to adjacent routers and receives processes; forwards LSPs from adjacent routers.
Decision: Runs the open-shortest-path-first algorithm based on the LSP database and creates the forwarding database. Next hop information and equal cost path sets create load balancing adjacency sets.
Forward: Compiles received LSPs. Forwarding database transmits LSPs to destination points. Redirects load sharing and generates error reports.