The
area feature is used in OSPF to divide a large network into small
segments. Any changes in one area will not cause any problem in other
areas, thus reducing routing table size and processor overhead also.
There are
three main types of area:
The
main purpose of stub area is to block the flooding from AS external
advertisements in OSPF and only OSPF injects a default router into a
stub area. In this tip we will discuss here only about stub area and
the remaining areas will be discussed in the next tips.
Follow the network topology of three different routers in given
figure:
There are some common OSPF configuration and Executable commands:
In this example we will not configure router C as stub area because
it is backbone router and does not participate in area 1. So we
will be concerned here only with router A and router B.
OSPF configuration on Router B as
stubby area
In global configuration mode
Router-B(config) # router ospf 1 (Here 1 indicates the
process identification number)
Router-B(config-Router) # network 20.0.0.0 0.255.255.255 area 1
(Here 20.0.0.0 indicates the network ID and 0.225.255.255 wildcard mask
with area 1)
Router-B(config-Router) # network 30.0.0.0 0.255.255.255 area 0
(Here 30.0.0.0 indicates the network ID and 0.225.255.255 wildcard mask
with area 0)
Router-B(config-Router) #area 1 stub (Here 1 indicate the
area ID and area 1 is designated as stubby area)
Router-B(config-Router) #exit (exit from ospf 1 on router B)
OSPF configuration on Router A as stubby area
In global configuration mode
Router-A(config) # router ospf 1 (Here 1 indicates the
process identification number)
Router-A(config-Router) # network 210.100.10.0 0.0.0.255 area 1
(Here 210.100.10.0 indicates the network ID and 0.0.0.255 wildcard mask
with area 1)
Router-A(config-Router) # network 20.0.0.0 0.255.255.255 area 1
(Here 20.0.0.0 indicates the network ID and 0.225.255.255 wildcard mask
with area 1)
Router-A(config-Router) #area 1 stub (Here 1 indicate the
area ID and area 1 is designated as stubby area)
Router-A(config-Router) #exit (exit from ospf 1 on router A)
COMPUTER TIPS