Level-1 routing and Level-2 routing

You can configure an IS-IS router to perform one or both of the following levels of IS-IS routing:

Note

The ISO/IEC specifications use the spelling "routeing", but this document uses the spelling "routing" to remain consistent with other Extreme documentation.

• Level-1 - A Level-1 router routes traffic only within the area the router is in. To forward traffic to another area, the Level-1 router sends the traffic to its nearest Level-2 router.
• Level-2 - A Level-2 router routes traffic between areas within a domain.

In Intermediate systems and end systems, Routers A and B are Level-1s only. Routers C and D are Level-1 and Level-2 ISs. Router E is a Level-1 IS only.