EIGRP中管理距离引起路由震荡的原因

EIGRP和OSPF做双点双向重分发

第一种情况：

1，R1,R2,R3,R4初始配置

R1

conf t

int l 0

ip add 1.1.1.1 255.255.255.255

int f0/0

ip add 1.1.123.1 255.255.255.0

no shut

router eigrp 1

no auto

net 1.1.1.1 0.0.0.0

net 1.1.123.0 0.0.0.255

end

R2

conf t

int l 0

ip add 1.1.2.2 255.255.255.255

int f0/0

ip add 1.1.123.2 255.255.255.0

no shut

int s1/0

ip add 1.1.234.2 255.255.255.0

encap f

no arp f

no frame inv

frame map ip 1.1.234.4 204 b

frame map ip 1.1.234.3 204 b

no shut

ip ospf p 0

router ospf 1

router-id 1.1.2.2

net 1.1.234.2 0.0.0.0 a 0

net 1.1.2.2 0.0.0.0 a 0

router eigrp 1

no auto

net 1.1.2.2 0.0.0.0

net 1.1.123.0 0.0.0.255

end

R3

conf t

int l 0

ip add 1.1.3.3 255.255.255.255

int f 0/0

ip add 1.1.123.3 255.255.255.0

no shut

int s1/0

ip add 1.1.234.3 255.255.255.0

encap f

no arp f

no frame inv

frame map ip 1.1.234.4 304 b

frame map ip 1.1.234.2 304 b

no shut

ip ospf p 0

router ospf 1

router-id 1.1.3.3

net 1.1.234.3 0.0.0.0 a 0

net 1.1.3.3 0.0.0.0 a 0

router eigrp 1

no auto

net 1.1.3.3 0.0.0.0

net 1.1.123.0 0.0.0.255

end

R4

conf t

int l 0

ip add 1.1.4.4 255.255.255.255

int s1/0

ip add 1.1.234.4 255.255.255.0

encap f

no arp f

no frame inv

frame map ip 1.1.234.2 402 b

frame map ip 1.1.234.3 403 b

no shut

router ospf 1

router-id 1.1.4.4

nei 1.1.234.2

nei 1.1.234.3

net 1.1.234.4 0.0.0.0 a 0

net 1.1.4.4 0.0.0.0 a 0

end

到这里，所有的EIGRP和OSPF邻居关系都建立好了。

2，在R2和R3上做双点双向重分发

R2

router eigrp 1

redistribute ospf 1 metric 10000 100 255 1 1500

router ospf 1

redistribute eigrp 1 metric 100 metric-type 1 subnets

end

R3

router eigrp 1

redistribute ospf 1 metric 10000 100 255 1 1500

router ospf 1

redistribute eigrp 1 metric 100 metric-type 1 subnets

end

重分发完成，

验证

R1路由表

R1#sh ip route

Gateway of last resort is not set

1.0.0.0/8 is variably subnetted, 6 subnets, 2 masks

D EX 1.1.4.4/32 [170/284160] via 1.1.123.3, 00:01:03, FastEthernet0/0

[170/284160] via 1.1.123.2, 00:01:03, FastEthernet0/0

D 1.1.3.3/32 [90/156160] via 1.1.123.3, 00:08:44, FastEthernet0/0

D 1.1.2.2/32 [90/156160] via 1.1.123.2, 00:08:44, FastEthernet0/0

C 1.1.1.1/32 is directly connected, Loopback0

C 1.1.123.0/24 is directly connected, FastEthernet0/0

D EX 1.1.234.0/24 [170/284160] via 1.1.123.3, 00:02:51, FastEthernet0/0

[170/284160] via 1.1.123.2, 00:02:51, FastEthernet0/0

R4路由表

R4#sh ip route

Gateway of last resort is not set

1.0.0.0/8 is variably subnetted, 6 subnets, 2 masks

C 1.1.4.4/32 is directly connected, Loopback0

O 1.1.3.3/32 [110/65] via 1.1.234.3, 00:00:14, Serial1/0

O 1.1.2.2/32 [110/65] via 1.1.234.2, 00:00:14, Serial1/0

O E1 1.1.1.1/32 [110/164] via 1.1.234.3, 00:00:14, Serial1/0

[110/164] via 1.1.234.2, 00:00:14, Serial1/0

O E1 1.1.123.0/24 [110/164] via 1.1.234.3, 00:00:14, Serial1/0

[110/164] via 1.1.234.2, 00:00:14, Serial1/0

C 1.1.234.0/24 is directly connected, Serial1/0

第二种情况

在R1的S1/2接口接入R5，并启用RIPV2

R5

conf t

int s1/2

ip add 192.168.45.5 255.255.255.0

no shut

router rip

ver 2

no auto

net 192.168.45.0

end

R1

conf t

int s1/2

no shut

ip add 192.168.45.4 255.255.255.0

router rip

ver 2

no au

net 192.168.45.0

end

把RIP再分发到EIGRP1中

router eigrp 1

redistribute rip metric 10000 100 255 1 1500

end

这时看R2和R3上的路由表

R2(config)#do sh 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

1.0.0.0/8 is variably subnetted, 6 subnets, 2 masks

O 1.1.4.4/32 [110/65] via 1.1.234.4, 00:31:58, Serial1/0

D 1.1.3.3/32 [90/156160] via 1.1.123.3, 00:05:56, FastEthernet0/0

C 1.1.2.2/32 is directly connected, Loopback0

D 1.1.1.1/32 [90/156160] via 1.1.123.1, 00:05:56, FastEthernet0/0

C 1.1.123.0/24 is directly connected, FastEthernet0/0

C 1.1.234.0/24 is directly connected, Serial1/0

O E1 192.168.45.0/24 [110/164] via 1.1.234.3, 00:05:59, Serial1/0

R2(config)#do ping 192.168.45.5

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 192.168.45.5, timeout is 2 seconds:

.....

Success rate is 0 percent (0/5)

仔细查看路由表可以发现，R2到192.168.45.0网段下一跳是1.1.234.2，也就是R3的S1/0接口，但是拓扑上表明下一跳为R1的F0/0接口为最佳路径。为什么会出现这样的情况呢？

我们知道，EIGRP的AD(管理距离）有两种情况：

1，当收到内部路由时，AD为90，路由表里的标识为“D”

2，当收到外部转发的路由是，AD为170，路由表里的标识为“ D EX”

当R1把RIP再分发到EIGRP1中的时候，R2和R3的收到192.168.45.0网段为“D EX"标识（可以通过shou ip bgp top命令校验)，这时EIGRP的AD为170，当R2把EIGRP1再分发到OSPF中后，因为的OSPF的AD为110，R3会从R1和R2这个两个路由器上收到192.168.45.0这个路由条目，根据路由选路原则，R3会优先选择OSPF协议收到的路由，所以在路由表上显示“O E1”，这样的结果会造成数据包在R4和R2之间震荡，

用trace命令验证

R2(config)#do trace 192.168.45.5

Type escape sequence to abort.

Tracing the route to 192.168.45.5

1 1.1.234.4 252 msec 232 msec 232 msec

2 1.1.234.3 432 msec 308 msec 304 msec

3 * * *

4 1.1.234.4 576 msec 612 msec 480 msec

5 1.1.234.3 720 msec 464 msec 648 msec

6 * * *

7 1.1.234.4 528 msec 684 msec 552 msec

8 1.1.234.3 888 msec 932 msec 672 msec

9 * * *

……

R3上也会出现相同的情况

解决方法

将R2和R3上OSPF的AD修改为大于170

R2

conf t

access 10 permit 192.168.45.0 0.0.0.255

router ospf 1

distance 180 1.1.3.3 0.0.0.0 10

end

R3

conf t

access 10 permit 192.168.45.0 0.0.0.255

router ospf 1

distance 180 1.1.2.2 0.0.0.0 10

end

验证R2，R3，R4路由表

R2(config)#do sh 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

1.0.0.0/8 is variably subnetted, 6 subnets, 2 masks

O 1.1.4.4/32 [110/65] via 1.1.234.4, 00:11:38, Serial1/0

D 1.1.3.3/32 [90/156160] via 1.1.123.3, 00:11:38, FastEthernet0/0

C 1.1.2.2/32 is directly connected, Loopback0

D 1.1.1.1/32 [90/156160] via 1.1.123.1, 00:11:38, FastEthernet0/0

C 1.1.123.0/24 is directly connected, FastEthernet0/0

C 1.1.234.0/24 is directly connected, Serial1/0

D EX 192.168.45.0/24 [170/284160] via 1.1.123.1, 00:11:38, FastEthernet0/0

R3(config)#do sh 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

1.0.0.0/8 is variably subnetted, 6 subnets, 2 masks

O 1.1.4.4/32 [110/65] via 1.1.234.4, 00:01:27, Serial1/0

C 1.1.3.3/32 is directly connected, Loopback0

D 1.1.2.2/32 [90/156160] via 1.1.123.2, 00:01:27, FastEthernet0/0

D 1.1.1.1/32 [90/156160] via 1.1.123.1, 00:01:27, FastEthernet0/0

C 1.1.123.0/24 is directly connected, FastEthernet0/0

C 1.1.234.0/24 is directly connected, Serial1/0

D EX 192.168.45.0/24 [170/284160] via 1.1.123.1, 00:01:27, FastEthernet0/0

R4#sh 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

1.0.0.0/8 is variably subnetted, 6 subnets, 2 masks

C 1.1.4.4/32 is directly connected, Loopback0

O 1.1.3.3/32 [110/65] via 1.1.234.3, 00:19:57, Serial1/0

O 1.1.2.2/32 [110/65] via 1.1.234.2, 00:19:57, Serial1/0

O E1 1.1.1.1/32 [110/164] via 1.1.234.3, 00:19:57, Serial1/0

[110/164] via 1.1.234.2, 00:19:57, Serial1/0

O E1 1.1.123.0/24 [110/164] via 1.1.234.3, 00:19:57, Serial1/0

[110/164] via 1.1.234.2, 00:19:57, Serial1/0

C 1.1.234.0/24 is directly connected, Serial1/0

O E1 192.168.45.0/24 [110/164] via 1.1.234.3, 00:12:25, Serial1/0

[110/164] via 1.1.234.2, 00:12:25, Serial1/0