1. OSPF：
它是由于互联网社会的需求而开发的，目的是为 TCP/IP 协议社区推出一个高功能的非专有 IGP。
OSPF是域内路由协议，基于链路状态路由技术。它引入了一些新概念，如路由更新认证、可变长度子网掩码 (VLSM)、根摘要等。
2. IS-IS :
中间系统到中间系统是一种标准化的链路状态协议，它被开发为 OSI 模型的最终路由协议。
IS-IS 是链路状态 IGP。链路状态协议通过在每个参与路由器上构建完整网络连接图所需的信息流通来区分。然后使用该地图计算到达目的地的最短路径。
主要用于ISP环境。
OSPF和IS-IS的区别：
| S.No. | Parameter | OSPF | IS-IS |
|---|---|---|---|
| 1. | Administrative Distance | 110 | 115 |
| 2. | Standard | RFC 2328 (OSPFv2). | ISO 10589, RFC 1195. |
| 3. | Operating OSI Layer | OSPF operates on the top of IP layer. | IS-IS operates over L2. |
| 4. | Virtual Links Supported | Yes | No |
| 5. | DR/BDR Election | OSPF elects a BDR and DR on broadcast networks. | IS-IS elects a single DIS on broadcast networks. |
| 6. | IP Connectivity | OSPF Requires the IP Connectivity between the routers to share the routing information. | IS-IS doesn’t require IP connectivity between the routers as updates are sent via CLNS instead of IP. |
| 7. | Support | OSPF supports NBMA and point to multipoint links. | IS-IS doesn’t support. |
| 8. | Router Area | OSPF router can belong to multiple areas. | IS-IS router can belong to only one area. |
| 9. | Area/Level Types |
Backbone Area Standard Area (Non Backbone Area) |
Level 1 Level 2 Level 1/2 Areas |
| 10. | Security | Prone to attack and hence requires more security overheads for protection. | Since, IS-IS runs on level2, hence every unlikely possibility of attack. |
| 11. | Identification | OSPF uses Router id to identify a router on network. | IS-IS uses System ID to identify a router on the network. |
| 12. | Flexibility | Less Flexible than IS-IS. | More Flexible to use than OSPF especially in provider domain. |
| 13. | Table Refresh | OSPF refreshes the entire routing table after 30 minutes. | IS-IS doesn’t refresh the entire SPF Table Periodically like OSPF. |
| 14. | Related Terms | Area, Non Backbone Area, Backbone Area, ABR, ASBR, Host. | IS, Level 1, Level 2, L1/L2, Subdomain, ES. |