What is Network Descriptor Block (NDB)?

It is the network information, which is stored in “Routing table” with Routing Descriptor Block (RDB). The memory to hold the IP routing table learned prefixes is divided into NDB and RDB. Each route in Routing information Base (RIB) requires one NDB and one RDB for each path. If the route is subnetted, additional memory is required in order to maintain the NDB, and the direct memory use for IP RIB can be shown with the show ip route summarycommand.