TECHNOLOGY

MPLS

IS-IS

Defined in the Standard ISO/IEC 10589, the intermediate system to intermediate system (IS-IS) protocol is also supported in the HSX 6000. Like OSPF, IS-IS is an IGP used for routing within an AS. An IS-IS router can be configured as either a Level 1, Level 2, or Level 1/Level 2 router. Level 1/Level 2 routers exchange link state information using link state packets (LSP) at both levels and as such must contain both Level 1 and Level 2 LSP databases.

Routers configured as either Level 1 or Level 2 exchange LSPs only in the configured level and maintain either a Level 1 or Level 2 LSP database. In the diagram below, each of the HSX 6000s are configured as a L1 router and are located within the same IS-IS area. To route a packet to another area, a L1 router must forward the packet to a L1/L2 router. When a L1/L2 router sends its L1 LSP into an area, it signals other L1 routers that it can reach another area.

Traffic engineering extensions for IS-IS are defined in RFC3784. Using these extensions, IS-IS can be used to distribute traffic engineering information within an AS. Traffic engineering information is maintained in a separate database called the traffic engineering database (TED). The TED can be queried to compute constraint based paths that are used to create traffic engineered connections through the network.

In the diagram below, the HSX 6000 is configured as a L1 IS-IS router and connected to L1/L2 distribution routers that are located in the core within the same IS-IS area. Only inter area L2 LSPs are flooded between the L2 core routers in the core area and L1/L2 distribute routers. The L1 routers in the same area as L1/L2 distribution routers exchange only L1 LSPs.