Down, Init, Two-way, Exstart, Exchange, Loading, Full

O processo de formação de adjacência consiste de sete estágios. Ao final, os roteadores que se tornaram adjacentes têm a mesma base de dados de link-state. Cada roteador é descrito por uma máquina de estados, que descreve a conversação entre ele e o seu vizinho. Os estados pelos quais uma interface passa na formação de adjacências são os seguintes:

Construindo Adjacências

















(cont.)

Down: Estado inicial. Nenhuma informação foi recebida de nenhum vizinho. Attempt: Em redes NBMA um vizinho aparenta estar down (nenhuma informação recente foi recebida do vizinho). Uma tentativa de contato deve ser feita, enviando pacotes hello a uma taxa diferenciada “PollInterval”. Init: a interface recebeu pacotes hello enviados recentemente pelo vizinho mas comunicação bi-direcional ainda não foi estabelecida. Two-way: Existe comunicação bi-direcional com o vizinho. O roteador se viu no pacote Hello do vizinho. Ao final deste estágio, a eleição do roteador DR e BDR foi realizada e adjacências podem ser estabelecidas. . Exstart: As inicializações necessárias para o estabelecimento de adjacências são feitas (número de seqüência inicial, quem é roteador primário e secundário, etc.). Exchange: Roteadores estão trocando LSAs. Loading: Neste estágio, os roteadores estão finalizando a troca de informações de roteamento carregadas pelos LSAs. Full: Neste estágio a adjacência está completa. Os roteadores vizinhos têm as suas bases de dados topológicas exatamente iguais.

Construindo Adjacências



Na figura, RTA, RTB, RTD e RTF compartilham um segmento comum (E0) na área 0.0.0.0. Os slides a seguir mostram as configurações de RTA e RTF. RTB e RTD têm configurações semelhantes à RTF (não são apresentados).

Exemplo

(cont.)

RTF# hostname RTF interface Ethernet0 ip address 203.250.14.2 255.255.255.0 router ospf 10 network 203.250.0.0 0.0.255.255 area 0.0.0.0

RTA# hostname RTA interface Loopback0 ip address 203.250.13.41 255.255.255.0 interface Ethernet0 ip address 203.250.14.1 255.255.255.0 router ospf 10 network 203.250.13.41 0.0.0.0 area 1 network 203.250.0.0 0.0.255.255 area 0.0.0.0

Exemplo







(cont.)

Com este comando pode-se verificar se todas as interfaces pertencem mesmo às áreas às quais elas supostamente devem pertencer. Observe que a seqüência na qual os comandos OSPF são listados é muito importante. Por exemplo, a configuração de RTA, se o comando "network 203.250.0.0 0.0.255.255 area 0.0.0.0" fosse colocado antes do comando "network 203.250.13.41 0.0.0.0 area 1" todas as interfaces estariam na área 0, o que é incorreto porque a interface de loopback está na área 1 e não na 0.0.0.0.

show ip ospf interface

O exemplo serve para demonstrar alguns comandos muito úteis quando se analisa redes OSPF. Um deles é:

Exemplo

(cont.)

RTF#show ip ospf interface e0 Ethernet0 is up, line protocol is up Internet Address 203.250.14.2 255.255.255.0, Area 0.0.0.0 Process ID 10, Router ID 203.250.15.1, Network Type BROADCAST, Cost: 10 Transmit Delay is 1 sec, State DR, Priority 1 Designated Router (ID) 203.250.15.1, Interface address 203.250.14.2 Backup Designated router (ID) 203.250.13.41, Interface address 203.250.14.1 Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 0:00:08 Neighbor Count is 3, Adjacent neighbor count is 3 Adjacent with neighbor 203.250.13.41 (Backup Designated Router)

RTA#show ip ospf interface e0 Ethernet0 is up, line protocol is up Internet Address 203.250.14.1 255.255.255.0, Area 0.0.0.0 Process ID 10, Router ID 203.250.13.41, Network Type BROADCAST, Cost: 10 Transmit Delay is 1 sec, State BDR, Priority 1 Designated Router (ID) 203.250.15.1, Interface address 203.250.14.2 Backup Designated router (ID) 203.250.13.41, Interface address 203.250.14.1 Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 0:00:02 Neighbor Count is 3, Adjacent neighbor count is 3 Adjacent with neighbor 203.250.15.1 (Designated Router) Loopback0 is up, line protocol is up Internet Address 203.250.13.41 255.255.255.255, Area 1 Process ID 10, Router ID 203.250.13.41, Network Type LOOPBACK, Cost: 1 Loopback interface is treated as a stub Host

Exemplo

(cont.)

RTB#show ip ospf interface e0 Ethernet0 is up, line protocol is up Internet Address 203.250.14.3 255.255.255.0, Area 0.0.0.0 Process ID 10, Router ID 203.250.12.1, Network Type BROADCAST, Cost: 10 Transmit Delay is 1 sec, State DROTHER, Priority 1 Designated Router (ID) 203.250.15.1, Interface address 203.250.14.2 Backup Designated router (ID) 203.250.13.41, Interface address 203.250.14.1 Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 0:00:03 Neighbor Count is 3, Adjacent neighbor count is 2 Adjacent with neighbor 203.250.15.1 (Designated Router) Adjacent with neighbor 203.250.13.41 (Backup Designated Router)

RTD#show ip ospf interface e0 Ethernet0 is up, line protocol is up Internet Address 203.250.14.4 255.255.255.0, Area 0.0.0.0 Process ID 10, Router ID 192.208.10.174, Network Type BROADCAST, Cost: 10 Transmit Delay is 1 sec, State DROTHER, Priority 1 Designated Router (ID) 203.250.15.1, Interface address 203.250.14.2 Backup Designated router (ID) 203.250.13.41, Interface address 203.250.14.1 Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 0:00:03 Neighbor Count is 3, Adjacent neighbor count is 2 Adjacent with neighbor 203.250.15.1 (Designated Router) Adjacent with neighbor 203.250.13.41 (Backup Designated Router)

Exemplo







Address 203.250.14.3 203.250.14.2 203.250.14.1

Interface Ethernet0 Ethernet0 Ethernet0

Observe que nenhum "Neighbor ID" pertence ao segmento em questão; entretanto, isto não é um erro. No exemplo, 203.250.12.1 e 203.250.15.1 não estão no segmento Ethernet 0, mas isto está OK porque o "Neighbor ID" é, na verdade, o endereço do Router ID (que em tese poderia ser qualquer endereço IP no “box”). RTD e RTB são apenas vizinhos, por isso é que o estado é 2WAY/DROTHER. RTD é adjacente a RTA e RTF, por isso estado é FULL/DR e FULL/BDR.

Dead Time 0:00:37 0:00:36 0:00:34

Um outro comando importante é o que permite examinar o estado dos vizinhos (“neighbors”) em um segmento particular:

(cont.)

RTD#show ip ospf neighbor Neighbor ID Pri State 203.250.12.1 1 2WAY/DROTHER 203.250.15.1 1 FULL/DR 203.250.13.41 1 FULL/BDR



Exemplo

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