An OSPF area – A working group!
As we saw in the OSPF Protocol course, Dijkstra's algorithm is a large algorithm.
OSPF uses the name AREA to divide a router group into several small working groups. If we put all our OSPF routers in the same area, it will work, but it will require a heavy workload for our routers to run this algorithm.
Let's say we have a company with 500 routers and 1000 sub-networks and everyone is in the same OSPF area. Each router in this area will run Dijkstra's algorithm for each subnetwork. When an interface of one of its 500 routers falls, ALL the routers of the OSPF area will recalculate all the paths for all our networks. All our routers will take a huge time to converge and their CPU loads are going to be full all the time…
– the LSDBs of our routers are smaller
– reducing the CPU load of our routers
– decrease in the number of LSA messages
Rules to follow:
– put all interfaces that belong to the same network in the same OSPF area
– an OSPF area should not be cut in half by another OSPF area
There are two types of OSPF routers:
– internal routers to an area: All its physical interfaces belong to the same OSPF area
– ABR -Aera Border Routers: Some of these interfaces are part of a non-backbone area and others are part of the backbone area
Any non-backbone area must have an ABR router connected to a Bakcbone area.
R1 (config) - ospf router [XXX] R1 (config-router) - networ[network]k[wildcard-mask] area [area-number]
in other words:
R1 (config) - router ospf 10 R1 (config-router) network 10.10.10.0 0.0.0.0.255 area 0
– Area 0 – Main Area
– all other areas must be directly connected to Area 0
– if this is not possible, it is possible to set up a virtual circuit (see the following course)
An ABR (Aera Border Routers) is a router that links two Area OSPF.
An ASBR (Autonomous System Boundary Router) is a router that links our OSPF bubble to another routing protocol.
– don't make OSPF areas with 50 routers (15 max)
– always rig area 0 first (in case you have only 5 routers for example
– remember this course, 'is the basis of OSPF!
Next course: Virtual Link
Hoping to have been able to help you!
Don't hesitate if you have any questions or if you have any information to bring!!