R1与R2配置单播后，它们与R3之间就不能更新路由了，因此也学不到R3中的路由。
实验图：
按照上图网络网络接口及EIGRP，然后配置R1与R2之间实现单播更新。
R1：
router eigrp 1
network 0.0.0.0
auto-summary
neighbor 10.0.0.2 FastEthernet0/0
R2:
router eigrp 1
network 0.0.0.0
auto-summary
neighbor 10.0.0.1 FastEthernet0/0
通过以上配置，
R1与R2可以更新路由，但与R3之间不能更新路由。
同理如果R1与R3配置了单播，则（R1和R3） 与R2之间就不能进行路由更新了。
R1上debug ip packet 结果
*Mar 1 00:30:51.235: IP: s=10.0.0.3 (FastEthernet0/0), d=224.0.0.10, len 60, rcvd 2
*Mar 1 00:30:51.239: IP: s=1.0.0.1 (local), d=224.0.0.10 (Loopback0), len 60, sending broad/multicast
*Mar 1 00:30:51.247: IP: s=1.0.0.1 (Loopback0), d=224.0.0.10, len 60, rcvd 2
*Mar 1 00:30:52.199: IP: s=10.0.0.1 (local), d=10.0.0.2 (FastEthernet0/0), len 60, sending
R1#
*Mar 1 00:30:52.523: IP: tableid=0, s=10.0.0.2 (FastEthernet0/0), d=10.0.0.1 (FastEthernet0/0), routed via RIB
*Mar 1 00:30:52.523: IP: s=10.0.0.2 (FastEthernet0/0), d=10.0.0.1 (FastEthernet0/0), len 60, rcvd 3
show ip route 结果
R1#show ip route
Codes: 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
Gateway of last resort is not set
C 1.0.0.0/8 is directly connected, Loopback0
D 2.0.0.0/8 [90/409600] via 10.0.0.2, 00:11:14, FastEthernet0/0
C 10.0.0.0/8 is directly connected, FastEthernet0/0
本文转自zcm8483 51CTO博客，原文链接:http://blog.51cto.com/haolun/993150
