Principle and configuration of OSPF multi-area
OSPF multi-area generation
Reasons for the generation of OSPF multi-area
Improve network scalability and
rapid convergence
Three kinds of traffic of OSPF
Intra-Area Traffic (Inter-Area Traffic)
The traffic constituted by the exchange of data packets between routers in a single area
Inter-Area Traffic (Inter-Area Traffic)
The traffic constituted by the exchange of data packets between routers in different areas.
External traffic ( External Traffic)
The traffic formed by the exchange of data packets between routers in the OSPF domain and routers outside the OSPF area or in another autonomous system
OSPF router type
The internal router
only saves the link state information in the
area. The area border router/ABR is
used to connect area 0 and other area
autonomous system border routers/ASBR is
used to connect the OSPF AS with other external routes.
OSPF area type
Backbone area Area 0
Non-backbone area-distinguished according to the types of routes that can be learned.
Standard
areas, stubs, and
totally stubby areas,
non-pure stubby areas (NSSA)
The ABR
summarizes the link status information of Area 1 and sends it to Area 0. It summarizes the link status information of
other areas and sends it to Area 1.
ASBR
ASBR is responsible for injecting external routes into the OSPF network.
ASBR-ABR
1. It can learn from other areas. routing
2. can learn external routes
OSPF link state database
The composition of the link state database
Each router has created a database composed of each interface, corresponding adjacent nodes and interface speed
. Each entry in the link state database is called LSA (Link State Advertisement). There are six common ones. Types of LSA
Link state advertisement (LSA) type
| Type code | description | use |
|---|---|---|
| Type 1 | Router LSA | Sent by routers in the area, describing the link status and cost of the router, and transmitted to the entire area |
| Type 2 | Network LSA | Issued by the DR in the area, describing the change information in the area, and passing it to the entire area |
| Type 3 | Network summary LSA | The summary link announcement issued by ABR in other areas describes the route of a certain network segment in other areas and is transmitted between areas |
| Type 4 | ASBR summary LSA | Issued by ABR, used to advertise ASBR information, determine the location of the ASBR, and will not appear in the area where the ASBR belongs |
| Type 5 | AS external LSA | Issued by ASBR, used to advertise external routes, tell the routers of the same AS the path to the external AS, and flood the entire AS |
| Type 7 | NSSA external LSA | The ASBR in the NSSA area is used to advertise the external routes connected to the area. Similar to Type 5, it is only flooded in the non-pure stub area, and will be converted to LSA5 by ABR during delivery. |
OSPF link state notification
Router's selection of routing entries
The router only adds the optimal routing entry to the routing table
. The basis for selecting routing entries.
Management distance
Metrics
Load balancing routing entries
OIA 3.3.3.3 [110/3] via 40.0.0.1, 00:41:13, FastEthernet1/0
[ 110/3] via 10.0.0.2,00:41:13, FastEthernet0/0
Peripheral area and complete peripheral area
Meet the following criteria area
is only a default route as its regional export
area can not pass through the area as a virtual links
Stub area where no autonomous system border router ASBR
is not the backbone area Area 0
peripheral area
not LSA4,5,7 notice
entirely peripheral region
except There is no LSA3, 4, 5, 7 notification except for a default route advertisement of LSA3
The role of the peripheral area and the complete peripheral area
Its main purpose is to reduce the LSA entries and routing entries in the area, and reduce the CPU and memory usage of the device. In the
peripheral area and the complete peripheral area, the ABR will automatically generate a default route and advertise it to the peripheral area or the complete peripheral area.
The actual operation of peripheral area configuration
No LSA4, 5, 7 advertise
ABR configuration
[R4] ospf 1
[R4-ospf-1]area 2
[R4-ospf-1-area-0.0.0.2] network xxxx xxxx-----Declare the directly connected network segment first , Then equipped with
[R4-ospf-1-area-0.0.0.2]stub
Intra-area routing configuration
[R5]ospf 1
[R5-ospf-1] area 2
[R4-ospf-1-area-0.0.0.2]network xxxx xxxx-----Declare the directly connected network segment first, then configure
[R5 -ospf-1-area-0.0.0.2]stub
[R5]display ip routing-table-----At this time, the route in the stub area will display a default route to the external area
Fully peripheral area configuration actual operation
ABR configuration
Except for a default route advertisement of LSA3, there is no advertisement of LSA3, 4, 5, 7
[R4]ospf 1
[R4-ospf-1]area 2
[R4-ospf-1]network xxxx xxxx-----first Declare the directly connected network segment, and configure
[R4-ospf-1-area-0.0.0.2] stub no-summary
intra - area routing configuration
[R5]ospf 1
[R5-ospf-1]area 2
[R5-ospf-1] network xxxx xxxx-----Declare the directly connected network segment first, and then configure
[R5-ospf-1-area-0.0.0.2]stub
[R5]display ip routing-table-----At this time, it is completely in the stub area The route will show a default route to other areas except this area