Thursday, June 30, 2011

How to perform route summarization in OSPF protocols?


  How to perform route summarization in OSPF protocols?

Route summarization is a process to merge a list of several routes into a single route. The main benefit of route summarization is to shrinking router tables and also reducing the size of update traffic. But the ultimate goal is to decrease the uses of bandwidth and processing time. For example if you are trying to advertise four different routes 196.1.17.0/24, 196.1.18.0/24, 196.1.19.0/24 and 196.1.20.0/24 from router A to router B then the only summarized address as 196.1.16.0 255.255.248.0 will be advertised in the update packet.  

In OSPF, you can perform two types of route summarization, inter-area route summarization and external route summarization. 
Today tip will help you configure OSPF route summarization between two different types of autonomous systems. In this case, we will try to configure two different routers with routing protocols OSPF & create four static routes and then advertised one summary route from router A to router B using summary-address command.
Follow the network topology of two different class network in given figure:
OSPF configuration on Router B 
In global configuration mode  
Router-B(config) # router ospf 1  (Here 1 indicate the process identification number)
Router-B(config-Router) # network 61.0.0.0 0.255.255.255 area 0 (Here 61.0.0.0 indicate the network ID and 0.225.255.255 wildcard mask with area 0) 
Router-B(config-Router) # network 210.100.30.0 0.0.0.255 area 0 (Here 210.100.30.0 indicate the network ID and 0.0.0.255 wildcard mask with area 0) 
OSPF configuration on Router A
In global configuration mode  
First create four static routes on router A and then advertised in Area 0.
Router-A(config)# ip route 196.1.17.0 255.255.255.0 null 0
Router-A(config)# ip route 196.1.18.0 255.255.255.0 null 0
Router-A(config)# ip route 196.1.19.0 255.255.255.0 null 0
Router-A(config)# ip route 196.1.20.0 255.255.255.0 null 0
Router-A(config) # router ospf 1  (Here 1 indicate the process identification number)
Router-A(config-Router) # network 61.0.0.0 0.255.255.255 area 0 (Here 61.0.0.0 indicate the network ID and 0.225.255.255 wildcard mask with area 0) 
Router-A(config-Router) # network 210.100.20.0 0.0.0.255 area 1 (Here 210.100.20.0 indicate the network ID and 0.0.0.255 wildcard mask with area 1)
Router-A(config-Router) # redistribute static subnet 
(Advertised static routes) 
Router-A(config-Router) # summary-address 196.1.16.0 255.255.248.0
(summary of four static routes)
Router-A(config-Router) #exit
Now verify the routes in router B routing table, run the command
Router-A# show ip route

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