Routing Protocols (2013) (796934), страница 3
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Used to minimize flapping link problem.Hold time - 10 seconds delay between rerunning SPF.Retransmit interval is time before repeated advertisement is sent if there was no ack).$OSPF Cisco metric =108bps $The cost of OSPF route is accumulated value from one router to the destination.Multiaccess network - network with more than 2 devices on the same shared media (e.g. ethernet LAN).OSPF network types:• point-to-point• broadcast multiaccess• nonbroadcast multiaccess (NBMA)• point-to-multipoint• virtual linksChallenges in multiaccess networks:• creation of multiple adjacencies $Total adjacencies =13n(n−1)$2• extensive flooding of LSAs (the problem is to introduce each device to other devices)DR and BDR are chosen to solve flooding problem (only in multiaccess).1.
DR is a router with highest interface priority.2. BDR is a router second highest interface priority.3. If priorities are equal ther compare by router IDs.4. Other router are marked as DROther.Neighbor states:• full• 2way (two drothers form adjacency)DR remains RD until:• DR fails• OSPF process on it fails• multiaccess interface on it failsRouters with priority 0 will never be DR or BDR.Autonomous system boundary router (ASBR) is located between OSPF routing domain and non-OSPFnetwork.OSPF area types:• Backbone area forms the kernel. It should distribute routing information between non-backboneareas.• Standard area is created by default. It receives link updates, summary routes and external routes.• Stub area don't receive information about external routes but receives it from other areas.• Totally stubbed area don'r receive information from other areas.
Cannot contain ASBR.LSA types:1. router link state update2. network link state3. summary network LSA4. ASBR summary5. AS external6. + some other ...14.
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