Overview
Intermediate System to Intermediate System (IS-IS) is a link-state protocol similar to OSPF. It was originally designed for the OSI protocol suite but was adapted for IP (Integrated IS-IS).
Key Characteristics
- Layer 2 Protocol: Runs directly on the data link layer, making it independent of the network layer protocol (IP).
- Scalability: Highly efficient and stable in very large networks.
- Levels: Uses Level 1 (intra-area) and Level 2 (inter-area) routing.
Comparison with OSPF
While OSPF is more common in enterprise environments, IS-IS is favored by many ISPs due to its simplicity and ability to handle large numbers of prefixes without instability.