Jika kita punya network 4 network misalnya:

192.168.1.0/24
192.168.2.0/24
192.168.3.0/24
192.168.4.0/24

Kita bisa melakukan autosummary ke 192.168.0.0/16 atau dengan subnet mask 255.255.0.0, atau jika mau lebih ramping kita dapat merubahnya ke notasi /22

R1(config-if)#int e0/0
R1(config-if)#ip summary-address eigrp 1 192.168.0.0 255.255.0.0
*Dec 23 10:02:19.123: %DUAL-5-NBRCHANGE: EIGRP-IPv4 1: Neighbor 192.168.1.2 (Ethernet0/0) is resync: summary configured

Sesaat setelah command diatas di apply maka di router akan segera muncul summary address telah sukses :

*Dec 23 10:02:19.123: %DUAL-5-NBRCHANGE: EIGRP-IPv4 1: Neighbor 192.168.1.2 (Ethernet0/0) is resync: summary configured
R2(config)#do sh ip ro
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
D 1.1.1.1 [90/409600] via 192.168.1.1, 00:25:24, Ethernet0/0
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback0
11.0.0.0/32 is subnetted, 1 subnets
D 11.11.11.11 [90/409600] via 192.168.1.1, 00:25:24, Ethernet0/0
22.0.0.0/32 is subnetted, 1 subnets
C 22.22.22.22 is directly connected, Loopback1
D 192.168.0.0/16 [90/409600] via 192.168.1.1, 00:08:17, Ethernet0/0
192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.1.0/30 is directly connected, Ethernet0/0
L 192.168.1.2/32 is directly connected, Ethernet0/0

Jika kita melihat ke router tetangganya dan melihat routing table nya, maka akan terlihat network sudah di summarize ke 192.168.0.0/16 , ini berarti summarization sudah berhasil dilakukan. Coba kita ping

R2(config)#do ping 192.168.6.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.6.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms

Pada router yang melakukan summarization prefix yang sebelumnya di summarisasi akan melalui interface Null0 pada routing table. Null0 interface bisa diibaratkan seperti blackhole, yang berarti semua packet yang dikirim menuju interface null0 tidak akan kembali lagi. EIGRP melakukan hal ini untuk menghindari routing loop

R1#sh ip ro
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
D 2.2.2.2 [90/409600] via 192.168.1.2, 00:45:37, Ethernet0/0
11.0.0.0/32 is subnetted, 1 subnets
C 11.11.11.11 is directly connected, Loopback1
22.0.0.0/32 is subnetted, 1 subnets
D 22.22.22.22 [90/409600] via 192.168.1.2, 00:45:30, Ethernet0/0
D 192.168.0.0/16 is a summary, 00:28:38, Null0
192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks

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