The default routes are
used to communicate with other network in totally stub area. LSAs 3, 4
and 5 are not advertised in totally stub area, only the default summary
routes are advertised in this area to reducing
the routing table size and processor overhead also.
The main
purpose of totally stub area is to block the flooding from
LSAs 3, 4 and 5
advertisements in OSPF and only OSPF injects a
default router into a totally stub area. In this tip we will discuss
here only about totally stub area and the remaining area types will be
discussed in the next tips.
Follow
the network topology of three different routers in given figure:
In this example we will configure router B as a totally stubby.
So we will be concerned here only with router B and then run simple ospf
protocol on other A and C routers.
OSPF configuration on Router B as totally 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 no-summary (Here 1
indicate the area ID and area 1 is designated as totally stubby area)
Router-B(config-Router) #exit (exit from ospf 1 on router B)
OSPF configuration on Router A
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) #exit (exit from ospf 1 on router A)
OSPF configuration on Router C
In global configuration mode
Router-C(config) # router ospf 1 (Here 1 indicates the
process identification number)
Router-C(config-Router) # network 210.100.30.0 0.0.0.255 area 0
(Here 210.100.30.0 indicates the network ID and 0.0.0.255 wildcard mask
with area 0)
Router-C(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-C(config-Router) #exit (exit from ospf 1 on router C)
COMPUTER TIPS