R1(config)#router eigrp 1
R1(config-router)#no auto-summary
R1(config-router)#network 192.168.13.0

R3(config)#router eigrp 1
R3(config-router)#no auto-summary

R1#
%DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 192.168.13.3 (FastEthernet0/0)
is up: new adjacency
R3#
%DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 192.168.13.1 (FastEthernet0/0)
is up: new adjacency
Let?s configure all the network commands so all routers become EIGRP neighbors and advertise
their networks:

R1(config)#router eigrp 1
R1(config-router)#network 192.168.12.0

R3(config)#router eigrp 1
R3(config-router)#network 192.168.34.0

R2(config)#router eigrp 1
R2(config-router)#no auto-summary
R2(config-router)#network 192.168.12.0
R2(config-router)#network 192.168.24.0

R4(config)#router eigrp 1
R4(config-router)#no auto-summary
R4(config-router)#network 192.168.24.0
R4(config-router)#network 192.168.34.0
R4(config-router)#network 4.0.0.0

Check show ip eigrp neighbors on all the devices,

R1#show ip route eigrp
4.0.0.0/24 is subnetted, 1 subnets
D 4.4.4.0 [90/158720] via 192.168.13.3, 00:21:48, FastEthernet0/0
D 192.168.24.0/24 [90/33280] via 192.168.13.3, 00:21:53 FastEthernet0/0
D 192.168.34.0/24 [90/30720] via 192.168.13.3, 00:21:50, FastEthernet0/0