- intra-area routers
- backbone routers
Explanation: Interarea summarization is manually configured on Area Border Routers (ABRs). Because ABRs connect multiple areas, it is these routers that would summarize routes before injecting them into another area. ASBRs are configured with external route summarization. Backbone and intra-area routers have all interfaces in a single area and are not able to summarize routes into other areas.