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4.intro to the IP Unicast Routing OSPF | LinkState Routing Layer 3 -…

- - - - Router ID
        router ID is 32-bit value to uniquely identify each router running the OSPF protocol can be configured manually but if not the OSPF can configure automatically > will choose a router id from the logical interface IP address
        and if we are creating the logical interface >> the OSPF wiil choose the Router ID from the physical interface
  - - - in the Broadcast Net there is many Routers attached to one Net Segment so they can discover each other as neighbors and synchronize LSDBs with each other >>
        each router synchronize LSDB with each other >> causes a lot of traffic soo for ythat The OSPF designs a disignated Router mechanism
        
        Designated Router
        Among all other routers > only one Router will be the Designated Router and all other routers synchronize their LSDBs with The Designated Router(same LSDB)
        
        Backup Designated Router
        if there is only one designated Router and it goes Down << other Routers will not be able to Synchronize
        
        for that we use the Backup Designated Router as backup > then Routers Synchronize with DR if its up and also eith the backup DR
        
        Neighbot States
        Afther Designing the DRand BDR the Neibor have 2 States
        
        Defines form of relationShip Btw Neighbors
        2 Nbors states are possible > Neighbor and Adjaccent
        
        Neighbor State
        2 Routers other than The DR and BDR can see each other
        Attached to the Same Net Seg
        
        Adjacent State
        relation Between DR and dBDR is adjacent
        LSDB is synchronized beetween these 2Routers
        
        RelationShiopp btw the 2 States
        Link State Establishemtn
        State Changes allow for neighbor relationShips to be achieved
        
        Adjacent
        
        ExStart
        
        Exchange
        
        2 more items...
        
        Neighbor
        
        Down
        
        Attempt
        
        1 more item...
        
        init
        
        2 more items...
        
        Neighbor Discoery
        The Hello Protocol is reponsible for neighbor discovery and maintenance for 2 way communication btw neighbors
        
        Designated Router Election
        A Designated Router is Elected based on the priorite value (whos DR and whos BDR)
        in Hello PAcket Priorite field contains priority of each router(bigger value higher priority) 0 means router will neven be elected as DR or BDR >> broadcast Net
        in P2P Net DR will not be elected (P2P ethernet link) and we can change manually the Net Type if we dont need The DR and BDR
        [RT]>interface GigabitEthernet0/0/0
        [interface]>ospf network-type p2p
        
        DataBase Synchronization
        After theDR and BDR is selected (already discovered each oter and dformed a neighbor relationShip)> they will Synchronize the LSDB
        for the P2P Net There is no [roblem concerning This
        When First Sychronizing they send themselves a list LSA in their LSDB
        each Router have an LSA but diffrent
        for that they use a DD(DatabaseDescritption) packet to exchange the list then they know each other from that list << if LSDB has already been the same > they dont need to exchange that list
        
        Neighboring routers form a master/slave relationship
        DB Description packets conatin LSA header information
        
        Establishing Full Adjency
        Missing ir newer instances of LSA are requested using LSR
        the Entire requested LSA is sent as an update
    - - Non Broadcast Multi-Access (NBMA)
        emulated the brodcast Net so the DR will still be chosem but because its not the same as the brodcast the DR selection should be careful
      - Point 2 MultiPoint
        emulated the P2P Net soo no DR will be selected on this NEt Type
  - - - OSPF Areas - Single Area
        a single link state database for the administrative domain
        Any Area bumber can be assigned but area 0 is recommanded
        The value of an area can be from 0.0.0.0 to 255.255.255.255.
        All of the links of the network need to be advertised in Area 0.
      - OSPF Areas - Multi Area
        in the Center of MutiArea Net is the Area 0 > backbone area / other normal areas must connect the backbone Area and exchange routes betwen area 0 and other Areas
        Areas build separate LS databases minimize impact of change
      - OSPF Network Advetisment (Area Config)
        [RT]>ospf 1 router id 1.1.1.1 (1 > process number)
        [RT-ospf]>area 0
        [area0]>network 192.168.1.0 0.0.0.255
        The NEt Command defines the Net to Be Advertised
        Route Advertisments are forwarded based on areas
        Configuraiton validation
        [RT]>display ospf peer
      - OSPF Authentification
        [RT]>interface GigabitEthernet0/0/0
        [interface]>ospf authentication-mode md5 1 passwd
        OSPF supp 2 form of auth, simple pass or crypto auth
        if passsws not the same in the 2 routers > they will not form a neighbor
        Configuration Validations
        [RT]terminal debugging
      - OSPF Silent Interface
        [RT]>ospf
        [ospf]>silent-interface GigabitEthernet0/0/0
        silent-interface command prevents an interface from forming neighbor relationships with peers
        Configuration Validation
        [RT]>display ospf 1 interface GigabitEthernet0/0/0