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Ip-default network
实验目的：验证ip-default network的工作原理及实验过程 实验拓扑：
Lo:1.1.1.1/24
12.1.1.0/24 S1/0 R1
S2/0 23.1.1.0/24
S1/0
S2/0
Lo:3.3.3.3/24
R2
Lo:2.2.2.2/24
网络边界
R3
实验过程：
基本配置 R1： hostname R1 ! interface Loopback0 ip address 1.1.1.1 255.255.255.0 ! interface Serial1/0 ip address 12.1.1.1 255.255.255.0 serial restart-delay 0 ! R2： hostname R2 ! interface Loopback0 ip address 2.2.2.2 255.255.255.0 ! interface Serial1/0 精品文档
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ip address 23.1.1.2 255.255.255.0 serial restart-delay 0 ! interface Serial2/0 ip address 12.1.1.2 255.255.255.0 serial restart-delay 0 ! R3： hostname R3 ! interface Loopback0 ip address 3.3.3.3 255.255.255.0 ! interface Serial2/0 ip address 23.1.1.3 255.255.255.0 serial restart-delay 0 ! 实验配置 R1： router eigrp 100 network 1.1.1.0 0.0.0.255 network 12.1.1.0 0.0.0.255 auto-summary ! R2： router eigrp 100 network 12.1.1.0 0.0.0.255 network 23.1.1.0 0.0.0.255 //想想其特别之处 auto-summary ! ip classless ip default-network 23.0.0.0 //通告默认路由配置 ip route 0.0.0.0 0.0.0.0 23.1.1.3 //与外网通信的静态默认路由配置 no ip http server no ip http secure-server ! R3： ip classless 精品文档
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ip route 0.0.0.0 0.0.0.0 23.1.1.2 //与内网通信的静态路由配置（通信是双向的） no ip http server no ip http secure-server ! 实验结论：
1. 实验详细说明：
此实验是用R1模拟内网，R2和R3模拟网络边界，把R1和R2运行在EIGRP 100内，R2和R3之间的通信是通过设置静态默认路由实现，R1与外网通信是通过R2通告的EIGRP默认路由完成的，R1与所有未知目的网段的通信都会通过R2实现，即R1要实现与外界的通信，若路由表中没有目的网段的路由，则会把包掷给R2。 2. 以上实验配置得出的实验信息： R1#sh ip route
Gateway of last resort is 12.1.1.2 to network 23.0.0.0 1.0.0.0/8 is variably subnetted, 2 subnets, 2 masks C 1.1.1.0/24 is directly connected, Loopback0 D 1.0.0.0/8 is a summary, 00:07:54, Null0
D* 23.0.0.0/8 [90/2681856] via 12.1.1.2, 00:06:48, Serial1/0 12.0.0.0/8 is variably subnetted, 2 subnets, 2 masks C 12.1.1.0/24 is directly connected, Serial1/0 D 12.0.0.0/8 is a summary, 00:07:54, Null0
R2#sh ip route
Gateway of last resort is 23.1.1.3 to network 0.0.0.0
D 1.0.0.0/8 [90/2297856] via 12.1.1.1, 00:09:12, Serial2/0 2.0.0.0/24 is subnetted, 1 subnets
C 2.2.2.0 is directly connected, Loopback0
* 23.0.0.0/8 is variably subnetted, 2 subnets, 2 masks C 23.1.1.0/24 is directly connected, Serial1/0 D* 23.0.0.0/8 is a summary, 00:09:01, Null0
12.0.0.0/8 is variably subnetted, 2 subnets, 2 masks C 12.1.1.0/24 is directly connected, Serial2/0 D 12.0.0.0/8 is a summary, 00:09:01, Null0 S* 0.0.0.0/0 [1/0] via 23.1.1.3
R3#sh ip route
Gateway of last resort is 23.1.1.2 to network 0.0.0.0 3.0.0.0/24 is subnetted, 1 subnets
C 3.3.3.0 is directly connected, Loopback0 23.0.0.0/24 is subnetted, 1 subnets
C 23.1.1.0 is directly connected, Serial2/0 S* 0.0.0.0/0 [1/0] via 23.1.1.2 R1#ping 3.3.3.3 sou 1.1.1.1 精品文档
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Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds: Packet sent with a source address of 1.1.1.1 !!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 40/40/40 ms
R1#ping 2.2.2.2 sou 1.1.1.1 Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds: Packet sent with a source address of 1.1.1.1 !!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 20/20/20 ms
3. 以上仅是做出想得到正确的实验结果的配置及实验信息，可能会很容易发现实验配置和
相应实验信息的一些条目被高亮显示，下面将针对这些被标注部分及可能存在的一些疑问进行具体分析：
疑问一：R2中的一条配置：network 23.1.1.0 0.0.0.255
对于这条配置可以与RIP默认路由实验中的相应配置作比较：在RIP的默认路由实验中，与外界路由器相连的那个网段23.1.1.0/24是不需要通告的，但是在EIGRP中是必须通告的。如果不通告这个网段，会出现下面的不同现象： R1#sh ip route
Gateway of last resort is not set
1.0.0.0/8 is variably subnetted, 2 subnets, 2 masks C 1.1.1.0/24 is directly connected, Loopback0 D 1.0.0.0/8 is a summary, 00:07:12, Null0
12.0.0.0/8 is variably subnetted, 2 subnets, 2 masks C 12.1.1.0/24 is directly connected, Serial1/0 D 12.0.0.0/8 is a summary, 00:07:12, Null0 R2#sh ip route
Gateway of last resort is 23.1.1.3 to network 0.0.0.0
D 1.0.0.0/8 [90/2297856] via 12.1.1.1, 00:08:11, Serial2/0 2.0.0.0/24 is subnetted, 1 subnets
C 2.2.2.0 is directly connected, Loopback0 * 23.0.0.0/24 is subnetted, 1 subnets
C 23.1.1.0 is directly connected, Serial1/0 12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, Serial2/0 S* 0.0.0.0/0 [1/0] via 23.1.1.3
可以发现与2中显示的路由条目相比，绿色条目消失了，橙色部分也有不同，默认路由设置不成功，当然R1与R3是不通的： R1#ping 3.3.3.3 精品文档
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Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds: .....
Success rate is 0 percent (0/5)
那么为什么R3必须要通告23.1.1.0/24这个网段而RIP不需要呢？我认为可以从EIGRP的三张表想一下，具体细节请读者自行研究。
疑问二：实验配置中R1和R2中的蓝色条目：auto summary
此实验是在没有关闭R1和R2的自动汇总前提下进行的，那若关闭自动汇总呢？会一切照常，还是会出现一些其他现象呢？
在关闭R1和R2的EIGRP自动汇总后（其余配置不变，仅在原实验配置基础上关闭auto summary），R1和R2路由表显示路由信息如下： R1#sh ip route
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 23.0.0.0/24 is subnetted, 1 subnets
D 23.1.1.0 [90/2681856] via 12.1.1.2, 00:05:08, Serial1/0 12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, Serial1/0 R2# sh ip route
Gateway of last resort is 23.1.1.3 to network 0.0.0.0
1.0.0.0/24 is subnetted, 1 subnets
D 1.1.1.0 [90/2297856] via 12.1.1.1, 00:06:18, Serial2/0 2.0.0.0/24 is subnetted, 1 subnets
C 2.2.2.0 is directly connected, Loopback0 * 23.0.0.0/24 is subnetted, 1 subnets
C 23.1.1.0 is directly connected, Serial1/0 12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, Serial2/0 S* 0.0.0.0/0 [1/0] via 23.1.1.3
可以发现与原实验显示的不同之处了，当然R1去ping 3.3.3.3是不通的。可以发现R2路由表中缺少了这个条目：
D* 23.0.0.0/8 is a summary, 00:09:01, Null0
这是关闭自动汇总后导致结果不同的直接原因，那么从这点可以看出R2必须开启auto summary，下面是关闭R1 auto summary、开启R2 auto summary下R1和R2的路由表中的信息：
R1#sh ip route
Gateway of last resort is 12.1.1.2 to network 23.0.0.0
1.0.0.0/24 is subnetted, 1 subnets
C 1.1.1.0 is directly connected, Loopback0 精品文档
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