Now, R1 is sending only one route to reach both subnets to R2. To do this, the following command can be used: We could configure R1 to advertise only one summary route for both subnets, which helps reduce R2’s routing table. R2 now has two routes for two subnets, which can be confirmed by using the show ip route command on R2: EIGRP advertises these subnets as two separate routes. Router R1 (on the left) has two directly connected subnets: 10.0.0.0/24 and 10.0.1.0/24.
#Cisco summary route calculator manual
The syntax of the command is: (config-if) ip summary-address eigrp ASN SUMMARY_ADDRESS SUBNET_MASKĪn example will help you to understand the concept of manual summarization: Manual summarization is configured on a per-interface basis. A single route can be used to represent multiple routes, which reduces the size of routing tables in a network.
One of the advantages of EIGRP over some other routing protocols (like OSPF) is that manual summarization can be done on any router within a network. Now R2 has the classless route to reach the subnet 10.0.1.0/24: Use the no auto-summary command to ensure it is turned off (it may already be disabled by default): This is why this feature is usually turned off (it is much better to use manual summarization to control exactly where and how summarization affects the network). The auto summary feature can cause problems with discontiguous networks. On R1, we have configured the following network statement:īut, because of the auto-summary feature, R2 receives the route to the classful network 10.0.0.0/8: With the auto summary feature turned on, R1 sends the classful route 10.0.0.0/8 to R2 instead of the more specific 10.0.1.0/24 route. Because of the auto summary feature, the router R1 summarizes the network 10.0.1.0/24 before sending the route to R2. Router R1 has the locally connected subnet 10.0.1.0/24 that is advertised to the router R2. To better understand the concept of auto-summarization, consider the following example. When auto-summary is enabled, routes are summarized to the classful boundary in the routing updates. EIGRP automatic summarizationĭepending on your IOS version, the EIGRP auto-summary feature might be enabled or disabled by default (it is more likely to be disabled in modern IOS versions). Two methods for summarizing routes exist: automatic summarization and manual summarization. It is often used in large networks with many subnets because it reduces the number of routes that the routers must maintain and minimizes routing updates. Route summarization is a method of representing multiple networks with a single summary address. EIGRP is not explicitly listed in the latest 200-301 version of the CCNA exam topics (whereas OSPF is) but you can still be tested on it in the exam.
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