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| The Distance Vector algorithm is one in which global information is given to local nodes - that is neighboring nodes. Below is a table of how a node interacts with it's peers. | The Distance Vector algorithm is one in which global information is given to local nodes - that is neighboring nodes. Below is a table of how a node interacts with it's peers, but first an example: |
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| . | {{{ B / \ A - C |\ \ | E D | / F---G Figure 1 }}} We build two tables 1. '''Initial''' distances stored at each node (global view) 2. '''Initial''' routing table at node A. ||Information Stored ||||||||||||||Distance to reach Node|| ||at Node A||A||B||C||D||E||F||G|| ||A||0||1||1||inf||1||1||inf|| ||B||1||0||1||inf||inf||inf||inf|| ||C||1||1||0||1||inf||inf||inf|| ||D||inf||inf||1||0||inf||inf||1|| ||E||1||inf||inf||inf||0||inf||inf|| ||F||1||inf||inf||inf||inf||0||1|| ||G||inf||inf||inf||1||inf||1||0|| ||Destination||Cost||Next Hop|| ||B||1||B|| ||C||1||C|| ||D||inf||-|| ||E||1||E|| ||F||1||F|| ||G||inf||-|| === Notes === |
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| * Routing loops between neighbors can be fixed with either SplitHorizon or SplitHorizon with poison reverse. | |
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| Example: InternetGatewayRoutingProtocol (IGRP) | Example: InteriorGatewayRoutingProtocol (IGRP) |
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Routing Algorithm
The Distance Vector algorithm is one in which global information is given to local nodes - that is neighboring nodes. Below is a table of how a node interacts with it's peers, but first an example:
B / \ A - C |\ \ | E D | / F---G Figure 1
We build two tables
Initial distances stored at each node (global view)
Initial routing table at node A.
Information Stored |
Distance to reach Node |
||||||
at Node A |
A |
B |
C |
D |
E |
F |
G |
A |
0 |
1 |
1 |
inf |
1 |
1 |
inf |
B |
1 |
0 |
1 |
inf |
inf |
inf |
inf |
C |
1 |
1 |
0 |
1 |
inf |
inf |
inf |
D |
inf |
inf |
1 |
0 |
inf |
inf |
1 |
E |
1 |
inf |
inf |
inf |
0 |
inf |
inf |
F |
1 |
inf |
inf |
inf |
inf |
0 |
1 |
G |
inf |
inf |
inf |
1 |
inf |
1 |
0 |
Destination |
Cost |
Next Hop |
B |
1 |
B |
C |
1 |
C |
D |
inf |
- |
E |
1 |
E |
F |
1 |
F |
G |
inf |
- |
Notes
Who: |
Broadcasts information to it's neighbors |
What: |
(Destination, Cost) tuples |
When: |
Periodically and when triggered by a change. Information is deleted after a time out. |
- Converges when the topology is static
- Suseptible to routing loops - race to infinity problem.
Routing loops between neighbors can be fixed with either SplitHorizon or SplitHorizon with poison reverse.
Example: InteriorGatewayRoutingProtocol (IGRP)
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