EIGRP的定義
EIGRP:Enhanced Interior Gateway Routing Protocol 即 增強內部網關路由線路協議。也翻譯為 加強型內部網關路由協議。 EIGRP是Cisco公司的私有協議。Cisco公司是該協議的發(fā)明者和唯一具備該協議解釋和修改權的廠商。 EIGRP結合了鏈路狀態(tài)和距離矢量型路由選擇協議的Cisco專用協議，采用彌散修正算法（DUAL）來實現快速收斂，可以不發(fā)送定期的路由更新信息以減少帶寬的占用，支持Appletalk、IP、Novell和NetWare等多種網絡層協議。
默認路由
默認路由是一種特殊的靜態(tài)路由,指的是當路由表中與包的目的地址之間沒有匹配的表項時路由器能夠做出的選擇·如果沒有默認路由，那么目的地址在路由表中沒有匹配表項的包將被丟棄· 默認路由在某些時候非常有效，當存在末梢網絡時，默認路由會大大簡化路由器的配置，減輕管理員的工作負擔，提高網絡性能。
實驗拓撲如下，路由器R1、R2、R3為內部路由器，而R4為外部路由，實驗目的為AS內部路由器發(fā)放默認路由，那么如何實現呢，請看下面步驟。
基礎配置如下：
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：通過在AS邊界路由器R3上重分發(fā)靜態(tài)的方式引入默認路由
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
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:通過手工宣告默認靜態(tài)路由，只是該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
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，注意在使用該方法時邊界路由器上要滿足三個條件，條件一：路由表中必須要有該主類路由條目(該主類的子網路由不算)，條件二：宣告時要同RIP一樣宣告該主類網絡，條件三：ip default-netwok 后的網絡也必須是主類網絡
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并沒有該主類網絡路由
Router eigrp 90
Network 34.0.0.0
R1:
R1#show ip route
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
其實我們不一定非要指定外網出接口作為默認網絡，可以使用環(huán)回接口作默認網絡可可控性也很強，只寫出簡單配置：
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
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
和上面做出比較，環(huán)回接口更加穩(wěn)定，此外可以減小一個路由條目，內網不需要公網的參與，編址也有所優(yōu)化，在網絡中只有使用ip defaul-netwok下放的不是全0的默認路由
方法4:由于EIGRP支持CIDR，而CIDR的極限就是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
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
以上就是Cisco網絡協議EIGRP向本區(qū)域下放默認路由的設置方法，謝謝閱讀，希望能幫到大家，請繼續(xù)關注VEVB武林網，我們會努力分享更多優(yōu)秀的文章。
