nível de rede
TRANSCRIPT
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Disciplina: Redes de Computadores
Nível de Rede
Profa. Débora Christina Muchaluat Saade
Departamento de Ciência da Computação - UFF
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Redes de Computadores
Distance Vector
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Redes de Computadores
Distance Vector
ü Também conhecido pelos nomes de • Algoritmo de roteamento de Bellman-Ford • Algoritmo de roteamento de Ford-Fulkerson
ü Algoritmo de roteamento utilizado pelos primeiros protocolos de nível de rede • “Antigo” algoritmo de roteamento da ARPANET
(até 1979) • RIP (Routing Information Protocol, RFC 1058) • IPX (primeiras versões) • DECnet (primeiras versões)
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Redes de Computadores
A
B
C
- 0 C
- ∞ A - ∞ B
D
Des
- ∞
Lin C
L3
L2 L1
- ∞ C
- 0 A - ∞ B
D
Des
- ∞
Lin C - ∞ C
- ∞ A - 0 B
D
Des
- ∞
Lin C
Distance Vector
D
L4
- ∞ C
- ∞ A - ∞ B
D
Des
- 0
Lin C
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Redes de Computadores
Distance Vector
ü Cada nó possui: • identificador único • custo de cada enlace
ü O nó transmite o seu vetor de distâncias (com destino/custo) para cada um dos seus vizinhos sempre que o seu vetor se modifica (ou periodicamente)
ü Cada nó mantém o vetor de distâncias mais recente enviado por cada um de seus vizinhos
ü Cada nó calcula o seu próprio vetor de distâncias, minimizando o custo para cada destino
ü O vetor de distâncias é recalculado sempre que: • um vizinho enviar um vetor de distâncias contendo informações
diferentes das anteriores • houver a queda em um enlace para um vizinho. Nesse caso, o vetor de
distâncias desse vizinho é descartado para que o vetor de distâncias do nó seja recalculado
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Redes de Computadores
Distance Vector
A
B
C
- ∞ A - ∞ B
C
Des
- 0
Lin C
9
3 5 - 0 A - ∞ B
C
Des
- ∞
Lin C
- ∞ A - 0 B
C
Des
- ∞
Lin C
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67
Redes de Computadores
Distance Vector
A
B
C
- ∞ A - ∞ B
C
Des
- 0
Lin C
9
3 5 - 0 A - ∞ B
C
Des
- ∞
Lin C
- ∞ A - 0 B
C
Des
- ∞
Lin C
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Redes de Computadores
Distance Vector
A
B
C
- ∞ A - ∞ B
C
Des
- 0
Lin C
9
3 5 - 0 A - ∞ B
C
Des
- ∞
Lin C
- ∞ A - 0 B
C
Des
- ∞
Lin C
C (3)
0 C ∞ B ∞ A C Des
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Redes de Computadores
Distance Vector
A
B
C
- ∞ A - ∞ B
C
Des
- 0
Lin C
9
3 5 - 0 A - ∞ B
C
Des
- ∞
Lin C
- ∞ A - 0 B
C
Des
C 3
Lin C
C (3)
0 C ∞ B ∞ A C Des
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Redes de Computadores
Distance Vector
A
B
C
- ∞ A - ∞ B
C
Des
- 0
Lin C
9
3 5 - 0 A - ∞ B
C
Des
- ∞
Lin C
- ∞ A - 0 B
C
Des
C 3
Lin C
C (3)
0 C ∞ B ∞ A C Des
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Redes de Computadores
Distance Vector
A
B
C
- ∞ A - ∞ B
C
Des
- 0
Lin C
9
3 5 - 0 A - ∞ B
C
Des
- ∞
Lin C
C (9)
- ∞ A - 0 B
C
Des
C 3
Lin C
C (3)
0 C ∞ B ∞ A C Des
0 C ∞ B ∞ A C Des
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Redes de Computadores
Distance Vector
A
B
C
- ∞ A - ∞ B
C
Des
- 0
Lin C
9
3 5 - 0 A - ∞ B
C
Des
C 9
Lin C
C (9)
- ∞ A - 0 B
C
Des
C 3
Lin C
C (3)
0 C ∞ B ∞ A C Des
0 C ∞ B ∞ A C Des
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Redes de Computadores
Distance Vector
A
B
C
- ∞ A - ∞ B
C
Des
- 0
Lin C
9
3 5 - 0 A - ∞ B
C
Des
C 9
Lin C
C (9)
- ∞ A - 0 B
C
Des
C 3
Lin C
C (3)
0 C ∞ B ∞ A C Des
0 C ∞ B ∞ A C Des
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Redes de Computadores
Distance Vector
A
B
C
- ∞ A - ∞ B
C
Des
- 0
Lin C
9
3 5 - 0 A - ∞ B
C
Des
C 9
Lin C
B (5)
C (9)
- ∞ A - 0 B
C
Des
C 3
Lin C
C (3)
0 C ∞ B ∞ A C Des
0 C ∞ B ∞ A C Des
3 C 0 B ∞ A C Des
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Redes de Computadores
Distance Vector
A
B
C
- ∞ A - ∞ B
C
Des
- 0
Lin C
9
3 5 - 0 A B 5 B
C
Des
B 8
Lin C
B (5)
C (9)
- ∞ A - 0 B
C
Des
C 3
Lin C
C (3)
0 C ∞ B ∞ A C Des
0 C ∞ B ∞ A C Des
3 C 0 B ∞ A C Des
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Redes de Computadores
Distance Vector
A
B
C
B 8 A B 3 B
C
Des
- 0
Lin C
9
3 5
8 C 5 B 0 A C Des
3 C 0 B 5 A C Des
A (9)
B (3)
- 0 A B 5 B
C
Des
B 8
Lin C
3 C 0 B 5 A C Des
0 C 3 B 8 A C Des
B (5)
C (9)
A 5 A - 0 B
C
Des
C 3
Lin C
8 C 5 B 0 A C Des
A (5)
0 C 3 B 8 A C Des
C (3)
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Redes de Computadores
Distance Vector
ü Vantagens • Simplicidade • Tempo de convergência baixo quando a rede opera
bem
ü Principal desvantagem • Tempo de convergência muito alto quando ocorrem
problemas na rede – Problema da contagem para infinito (count-to-infinity
problem)
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Redes de Computadores
Distance Vector
A
B
C
- 0 C Des Lin C
1 C C Des
B
C Des
B 2 Lin C
1 C C Des
B
C Des
C 1 Lin C
0 C C Des
C 2 C C Des
A
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Redes de Computadores
Distance Vector
A
B
C
- 0 C Des Lin C
1 C C Des
B
C Des
B 2 Lin C
1 C C Des
B
C Des
C 1 Lin C
0 C C Des
C 2 C C Des
A
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Redes de Computadores
Distance Vector
A
B
C
- 0 C Des Lin C
C Des
B 2 Lin C
1 C C Des
B
C Des
C 1 Lin C
2 C C Des
A
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Redes de Computadores
Distance Vector
A
B
C
- 0 C Des Lin C
C Des
B 2 Lin C
1 C C Des
B
C Des
A 3 Lin C
2 C C Des
A
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Redes de Computadores
Distance Vector
A
B
C
- 0 C Des Lin C
C Des
B 2 Lin C
1 C C Des
B
C Des
A 3 Lin C
2 C C Des
A
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Redes de Computadores
Distance Vector
A
B
C
- 0 C Des Lin C
C Des
B 4 Lin C
3 C C Des
B
C Des
A 3 Lin C
2 C C Des
A
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Redes de Computadores
Distance Vector
A
B
C
- 0 C Des Lin C
C Des
B 4 Lin C
3 C C Des
B
C Des
A 3 Lin C
2 C C Des
A
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Redes de Computadores
Distance Vector
A
B
C
- 0 C Des Lin C
C Des
B 4 Lin C
3 C C Des
B
C Des
A 5 Lin C
4 C C Des
A
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Redes de Computadores
Distance Vector
ü Diversas propostas para melhorar a questão do tempo de convergência [Perlman 1999]
• Split Horizon: a distância ao nó X não é reportada na linha por onde pacotes com destino X são encaminhados – poison reverse: a distância é
reportada como sendo infinito ü Nenhuma das propostas resolve a questão
satisfatoriamente
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Redes de Computadores
Distance Vector – Split Horizon & Poison Reverse
A
B
C
- 0 C Des Lin C
∞ C C Des
B
C Des
B 2 Lin C
1 C C Des
B
C Des
C 1 Lin C
0 C C Des
C ∞ C C Des
A
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Redes de Computadores
Distance Vector – Split Horizon & Poison Reverse
A
B
C
- 0 C Des Lin C
∞ C C Des
B
C Des
B 2 Lin C
1 C C Des
B
C Des
C 1 Lin C
0 C C Des
C ∞ C C Des
A
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Redes de Computadores
Distance Vector – Split Horizon & Poison Reverse
A
B
C
- 0 C Des Lin C
C Des
B 2 Lin C
1 C C Des
B
C Des
C 1 Lin C
∞ C C Des
A
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Redes de Computadores
Distance Vector – Split Horizon & Poison Reverse
A
B
C
- 0 C Des Lin C
C Des
B 2 Lin C
1 C C Des
B
C Des
- ∞ Lin C
∞ C C Des
A
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Redes de Computadores
Distance Vector – Split Horizon & Poison Reverse
A
B
C
- 0 C Des Lin C
C Des
B 2 Lin C
1 C C Des
B
C Des
- ∞ Lin C
∞ C C Des
A
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Redes de Computadores
Distance Vector – Split Horizon & Poison Reverse
A
B
C
- 0 C Des Lin C
C Des
- ∞ Lin C
∞ C C Des
B
C Des
- ∞ Lin C
∞ C C Des
A