EIGRP默认路由的下放
实验拓扑如下，路由器R1、R2、R3为内部路由器，而R4为外部路由，实验目的为AS内部路由器发放默认路由
基础配置如下：
R1:
interface Loopback0
ip address 1.1.1.1 255.255.255.0
!
interface FastEthernet0/0
ip address 12.1.1.1 255.255.255.0
!
router eigrp 90
network 0.0.0.0
no auto-summary
!
========================================================
R2:
interface Loopback0
ip address 2.2.2.2 255.255.255.0
!
interface FastEthernet0/0
ip address 23.1.1.2 255.255.255.0
!
interface FastEthernet0/1
ip address 12.1.1.2 255.255.255.0
!
router eigrp 90
network 0.0.0.0
no auto-summary
========================================================
R3:
interface Loopback0
ip address 3.3.3.3 255.255.255.0
!
interface FastEthernet0/1
ip address 23.1.1.3 255.255.255.0
!
interface Serial1/0
ip address 34.1.1.3 255.255.255.0
!
router eigrp 90
network 23.1.1.3 0.0.0.0
no auto-summary
=========================================================
R4:
interface Loopback0
ip address 4.4.4.4 255.255.255.0
!
interface Serial1/1
ip address 34.1.1.4 255.255.255.0
!
ip route 0.0.0.0 0.0.0.0 Serial1/1 34.1.1.3
=========================================================
方法1：通过在AS边界路由器R3上重分发静态的方式引入默认路由
在R3配置如下：
R3:
ip route 0.0.0.0 0.0.0.0 Serial1/0 34.1.1.4
Router eigrp 90
Redistribute static
R1:
R1#show ip rou
<ommit output>
Gateway of last resort is 12.1.1.2 to network 0.0.0.0
1.0.0.0/24 is subnetted, 1 subnets
C 1.1.1.0 is directly connected, Loopback0
2.0.0.0/24 is subnetted, 1 subnets
D 2.2.2.0 [90/409600] via 12.1.1.2, 00:15:47, FastEthernet0/0
23.0.0.0/24 is subnetted, 1 subnets
D 23.1.1.0 [90/307200] via 12.1.1.2, 00:14:57, FastEthernet0/0
12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, FastEthernet0/0
D*EX 0.0.0.0/0 [170/2221056] via 12.1.1.2, 00:03:44, FastEthernet0/0
方法2:通过手工宣告默认静态路由，只是该路由不能指定下一跳
R3:
Ip route 0.0.0.0 0.0.0.0 serial 1/0
Router eigrp 90
Network 0.0.0.0
R1:
R1#show ip rou
<ommit output>
Gateway of last resort is 12.1.1.2 to network 0.0.0.0
34.0.0.0/24 is subnetted, 1 subnets
D 34.1.1.0 [90/2221056] via 12.1.1.2, 00:02:57, FastEthernet0/0
1.0.0.0/24 is subnetted, 1 subnets
C 1.1.1.0 is directly connected, Loopback0
2.0.0.0/24 is subnetted, 1 subnets
D 2.2.2.0 [90/409600] via 12.1.1.2, 00:23:44, FastEthernet0/0
3.0.0.0/24 is subnetted, 1 subnets
D 3.3.3.0 [90/435200] via 12.1.1.2, 00:02:57, FastEthernet0/0
23.0.0.0/24 is subnetted, 1 subnets
D 23.1.1.0 [90/307200] via 12.1.1.2, 00:22:55, FastEthernet0/0
12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, FastEthernet0/0
D* 0.0.0.0/0 [90/2221056] via 12.1.1.2, 00:00:03, FastEthernet0/0
方法3:使用ip default-network x.x.x.x，注意在使用该方法时边界路由器上要满足三个条件，条件一：路由表中必须要有该主类路由条目（该主类的子网路由不算），条件二：宣告时要同RIP一样宣告该主类网络，条件三：ip default-netwok 后的网络也必须是主类网络
D* 0.0.0.0/0 [90/2221056] via 12.1.1.2, 00:00:03, FastEthernet0/0
R3:
Ip default-network 34.0.0.0
Ip route 34.0.0.0 255.0.0.0 serial 1/0 34.1.1.4 //R3并没有该主类网络路由
Router eigrp 90
Network 34.0.0.0
R1:
R1#show ip route
<ommit output>
Gateway of last resort is 12.1.1.2 to network 34.0.0.0
34.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
D 34.1.1.0/24 [90/2221056] via 12.1.1.2, 00:02:11, FastEthernet0/0
D* 34.0.0.0/8 [90/2221056] via 12.1.1.2, 00:00:14, FastEthernet0/0
1.0.0.0/24 is subnetted, 1 subnets
C 1.1.1.0 is directly connected, Loopback0
2.0.0.0/24 is subnetted, 1 subnets
D 2.2.2.0 [90/409600] via 12.1.1.2, 00:02:11, FastEthernet0/0
23.0.0.0/24 is subnetted, 1 subnets
D 23.1.1.0 [90/307200] via 12.1.1.2, 00:02:11, FastEthernet0/0
12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, FastEthernet0/0
其实我们不一定非要指定外网出接口作为默认网络，可以使用环回接口作默认网络可可控性也很强，只写出简单配置：
C 12.1.1.0 is directly connected, FastEthernet0/0
R3：
Ip default-network 192.168.10.0
Interface loopback 1
Ip address 192.168.10.1 255.255.255.0
Router eigrp 90
Network 192.168.10.0
R1:
R1#show ip rou
<ommit output>
Gateway of last resort is 12.1.1.2 to network 192.168.10.0
1.0.0.0/24 is subnetted, 1 subnets
C 1.1.1.0 is directly connected, Loopback0
2.0.0.0/24 is subnetted, 1 subnets
D 2.2.2.0 [90/409600] via 12.1.1.2, 00:08:12, FastEthernet0/0
D* 192.168.10.0/24 [90/435200] via 12.1.1.2, 00:00:08, FastEthernet0/0
23.0.0.0/24 is subnetted, 1 subnets
D 23.1.1.0 [90/307200] via 12.1.1.2, 00:08:12, FastEthernet0/0
12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, FastEthernet0/0
和上面做出比较，环回接口更加稳定，此外可以减小一个路由条目，内网不需要公网的参与，编址也有所优化，在网络中只有使用ip defaul-netwok下放的不是全0的默认路由
方法4:由于EIGRP支持CIDR，而CIDR的极限就是0.0.0.0/0
C 12.1.1.0 is directly connected, FastEthernet0/0
R3:
Interface fastethernet 0/1
Ip summary-address eigrp 90 0.0.0.0 0.0.0.0
R1:
R1#show ip rou
<ommit output>
Gateway of last resort is 12.1.1.2 to network 0.0.0.0
1.0.0.0/24 is subnetted, 1 subnets
C 1.1.1.0 is directly connected, Loopback0
2.0.0.0/24 is subnetted, 1 subnets
D 2.2.2.0 [90/409600] via 12.1.1.2, 00:16:44, FastEthernet0/0
23.0.0.0/24 is subnetted, 1 subnets
D 23.1.1.0 [90/307200] via 12.1.1.2, 00:16:44, FastEthernet0/0
12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, FastEthernet0/0
D* 0.0.0.0/0 [90/332800] via 12.1.1.2, 00:00:02, FastEthernet0/0