Cabletron Systems CyberSWITCH CSX400 Installation Manual

Also see for CyberSWITCH CSX400: Setup guide Configuration guide User guide User guide User guide

Contents

CSX400 Firmware SupportCyberSWITCH CSX400 and CSX400-DC Installation Guide2-13Every autonomous system within an OSPF routing domain must have a backbone. An OSPFbackbone distributes routing information between areas in an autonomous system and consists ofall area border routers, any networks not completely contained in any area and their attachedrouters. The backbone of a autonomous system is an OSPF area possessing an area id of 0.0.0.0.AreasAreas are groups of networks and attached hosts. A router’s topology database includes area links,and summarized and external links depicting the autonomous system topology. From thisdatabase, routers calculate a route using the shortest-path tree algorithm.The Hello ProtocolThe Hello Protocol establishes and maintains neighbor relationships, and ensures bidirectionalcommunications among neighboring routers. Hello packets are sent out all router portsperiodically. A designated router is chosen by the Hello Protocol on multiaccess networks andcontrols adjacencies formed over the network.Neighbors and AdjacencyThe OSPF routing protocol establishes adjacencies among neighboring routers which facilitate theexchange of routing information. Neighboring routers have interfaces to a common network andare discovered by OSPF’s Hello Protocol.Area Border RouterArea Border Routers (ABR) connect networks together. These routers have multiple interfaces andparticipate in multiple areas. There must be at least one area border router in each area connectingthat area to a backbone. An ABR maintains a separate link-state database per area that it is attachedto. This version of Routing Services does not include this functionality.Designated RouterDesignated Routers (DR) are used by OSPF to reduce adjacencies. Other routers establishadjacencies and synchronize databases only with the designated router and backup designatedrouter. These routers perform two key functions for the OSPF routing protocol:• The designated router creates a network links advertisement which lists the set of routers,including the designated router, attached to the network.• The designated router is adjacent to all routers on the network and plays a central role in thesynchronization of link-state databases across adjacencies.One DR is elected for each area and is elected by using the Hello Protocol. The DR electionprocess starts when the router doing the calculation removes ineligible routers from the list ofpotential Designated Routers. This includes routers with a router priority of 0.