OSPF Neighbors

OSPF neighbor relationship vs adjacency There is a distinction between OSPF neighbors and OSPF adjacent neighbors. OSPF neighbors are routers running OSPF and have one or more common connected subnet. OSPF adjacent neighbors, however, are routers that established adjacency by ... Read More »

OSPF DR BDR Election

OSPF DR and BDR The Designated Router concept is a link-specific concept, not for the whole router. A router can be a DR on one link, a BDR on second link and a DROTHER on a third link. DR and BDR election ... Read More »

OSPF Timers

OSPF Timers OSPF Hello timer To discover neighbors and establish adjacency, OSPF routers exchange Hello packets at regular intervals called Hello timers. These Hello packets are sent to Multicast address group Hello replies are unicast. The Hello packet timer has ... Read More »

OSPF Network Types

OSPF network types There are three types of networks that are known to OSPF: point to point broadcast non broadcast multiaccess NBMA For each one of these network types, OSPF has an operational mode. The default operational modes are not ... Read More »


OSPF LSA Type 1: Router LSA flooded within the area generated by each router the Link State ID = the router ID of the sending router provides information about directly connected networks OSPF LSA Type 2: Network LSA flooded within ... Read More »

OSPF Route Filtering


In this article, we are going to learn how to filter routes in OSPF. We will learn how to do that within an area, and between areas. Network topology We will use the following topology. Everything is done in GNS3. I ... Read More »