1 min read
ISIS Cheat Sheet
| ISIS – Interior Gateway Protocol (IGP) | |
| Type: | Link State |
| Algorithm: | Dijkstra |
| Metric: | 10 for any interface 0 for Loopback interface |
| Metric Type: | Narrow and Wide by default. But, ISIS silently limits metric to 63. In modern ISIS deployments we should enable wide-metric-only. |
| Preference (AD): | 15 / 18 (L1/L2 Internal) 160 / 165 (L1/L2 External) |
| PDU Types | ||
| IIH | IS-IS hello | Identify neighboring ISIS system and establish adjacencies |
| LSP | Link-state PDUs | Used to advertise link-state information about themselves and their connected links to other routers in the network. |
| CSNP | Complete Sequence Number PDU | Contain a complete list of all link-state PDUs in the IS-IS database |
| PSNP | Partial Sequence Number PDU | Message used to acknowledge received LSPs or request missing LSPs during database synchronization. |
| ISIS L1/L2 Redistribution | |
| By default: | L1 to L2 are redistributed. |
| By default: | L2 to L1 are not redistributed. |
| By default: | External L1 are not redistributed to L2. |
| With wide-metrics-only configured: | IPv4 External L1 routes become internal, so they pass to L2. |
| With wide-metrics-only configured: | IPv6 External L1 routes are not redistributed to L2. |