The Impact of a Link-state Change
- OSPF is link-state
- Is it up/down, what is the speed? these are things that OSPF routers will be discussing with each other.
- Based on these paths what is the best one to take?
- Link State Advertisements are used
- LSA's are generated when a link changes state
- Neighbors perform recalculation
- OSPF routers in the same subnet are known as neighbors
- Form neighbors via hello messages sent on the multicast address 2224.0.0.5
- Default Hello timer is 10 seconds
- Best routes are installed in the routing table
OSPF Storytime...
- It can lead to high utilization
- A big company with:
- warehouses
- Datacenter with fast switches
- Headquarters were they have many employees working
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Advantages of Multi-area OSPF
- Summarization
- Dijkstra takes more CPU, therefore more time.
- Isolation of topology changes
- An area can have multiple subnets
- Reduces complexity
- Clean routing tables to look at
- Improved stability
- Reduced hardware requirements
- It is really nice to go into existing hardware, tweak and tun it and get even more out of it.
- Why don't we put one general route out there
- It isolates topology changes
- It will go from a large database that can be impacted by topology changes to a smaller database (calculating less often).
- Redistribution
- Perform tuning for network environments
OSPF Router Types
- Internal Router
- Area Border Router (ABR)
- Autonomous System Boundary (ASBR)
- Backbone
- Internal router with area 0
- Sometime we have mergence
- We can connect a RIP environment with an OSPF environment.
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OSPF Area Operations
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