Abstract:IS-IS is a link state routing protocol, which is introduced into the TCP/IP protocol stack because of its high efficient and stable features from the OSI protocol stack. IS-IS supports both the CLNP and the IP routing. On the basis of the in-depth study of IS-IS protocol by NSAP address, area type, message analysis and working principle, an IS-IS experimental network model of multi-region and multi-network is designed, and it is successfully realized through the Dynamips simulation platform. The simulation results verify the mechanism and principle of IS-IS protocol with the analysis of packet capture and neighbor table, topology table, and LSDB, which can provide reference for deployment in the actual network, and the instance can be migrated to the actual network seamlessly.