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Differential Hellos Differential Hellos report only changes in neighbor states. Hellos also report full or partial neighbor information periodically, to provide 2-hop neighbor information to neighbors. Using differential Hellos allows Hellos to be sent more frequently, allowing faster response to topology changes. Changes to 2-hop neighbor information are reported quickly in differential Hellos. The CDS algorithms require only partial 2-hop neighbor information, i.e., the (Backup) Dependent Neighbors of each neighbor. Thus, only Dependent Neighbors need to be reported periodically in Hellos. In particular non-DR/BDR routers (which have no Dependent Neighbors) only need to send differential Hellos, and never need to send full Hellos or report any neighbor information periodically. Advantage of CDS approach: A non-DR/BDR router never needs to include all of its neighbors in either a Hello or an LSA. |