按需路由选择原理
静态路由的缺点是，必须手工配置，同时在网络拓扑变化后需要手工更新；动态路由选择协议的缺点是，它们需要占用网络带宽和路由器资源。在包含数百个分支点的中央-分支网络中，采用静态路由时配置工作量将非常大；而采用动态路由选择协议时将占用大量的资源。
在这种情况下，可采用第三种方式：按需路由选择（ODR）。ODR使用Cisco发现协议（CDP）来在分支（末节）路由器和中央路由器之间传输网络信息。与动态路由选择协议相比，ODR提供IP路由选择信息的开销非常小；而与静态路由相比，ODR的手工配置量更少。
ODR只适合用于中央-分支拓扑。在这种拓扑中，每台分支路由器只与中央路由器相邻。分支路由器也被称为末节路由器。末节路由器可能连接了几个LAN，但通常只有一条到中央路由器的WAN连接。中央路由器需要获悉每台分支路由器连接的网络，而分支路由器只需要一条指向中央路由器的默认路由。
配置ODR后，末节路由器使用CDP将IP前缀信息发送给中央路由器。末节路由器发送其所有直连网络的前缀信息。ODR报告子网掩码，因此支持变长子网掩码（VLSM）。
ODR依赖于CDP在中央路由器和分支路由器之间传输信息，因此在中央路由器和分支路由器之间的所有链路上都必须启用CDP。默认情况下，Cisco路由器全局地启用CDP，并在各个接口上启用CDP。然而，在有些WAN链路（如ATM）上，必须显式地启用CDP。
中央路由器将一条指向自己的默认路由发送给分支路由器，并将ODR报告的末节网络加入到路由选择表中，可对中央路由器进行配置，使之将这些网络重分发给动态路由选择协议。中央路由器将ODR报告分支路由器的IP地址用作下一跳地址。
ODR并非一种路由选择协议，因为它交换的信息仅限于IP前缀和默认路由。ODR不报告度量值，对于ODR报告的所有路由，中央路由器都将其度量值设置为1跳。然而，使用ODR，可以动态地获悉有关末节网络的路由选择信息，而不存在动态路由选择协议所需的开销；同时，无需手工配置，就能够给末节路由器提供一条默认路由。
ODR简介:
ODR技术(IOS 12.0.5T)能够使hub and spoke网络结构中的hub路由器自动地向spoke路由器(又称为stub站点)提供缺省路由,stub站点路由器不需要运行动态路由协议,也不需要配置任何的静态路由,几乎没有系统资源的占用,就能够实现本地所有的直连子网向hub路由器的自动通告.
ODR技术(IOS 12.0.5T)能够使hub and spoke网络结构中的hub路由器自动地向spoke路由器(又称为stub站点)提供缺省路由,stub站点路由器不需要运行动态路由协议,也不需要配置任何的静态路由,几乎没有系统资源的占用,就能够实现本地所有的直连子网向hub路由器的自动通告.
3.ODR需求:
ODR使用Cisco Discovery Protocol (CDP)在hub路由器和spoke路由器之间传递路由信息,因此需要在hub和spoke路由之间的每条链路上启用cdp协议,cdp是一个data-link层协议,可以运行在Lan/serial/frame-relay/atm等传输介质上.
ODR使用Cisco Discovery Protocol (CDP)在hub路由器和spoke路由器之间传递路由信息,因此需要在hub和spoke路由之间的每条链路上启用cdp协议,cdp是一个data-link层协议,可以运行在Lan/serial/frame-relay/atm等传输介质上.
4.(.NET文件的)拓扑图如下:
autostart = False
[localhost]
`3640`
p_w_picpath = C:\Program Files\Dynamips\p_w_picpaths\C3640-JS.BIN
ram = 128
idlepc = 0xffffffff80425144
confreg = 0x2142
`3640`
p_w_picpath = C:\Program Files\Dynamips\p_w_picpaths\C3640-JS.BIN
ram = 128
idlepc = 0xffffffff80425144
confreg = 0x2142
`ROUTER Router1`
model = 3640
console = 2001
slot0 = NM-1E
slot1 = NM-4T
E0/0 = Router2 E0/0
S1/0 = Router3 S1/0
S1/1 = Router4 S1/1
model = 3640
console = 2001
slot0 = NM-1E
slot1 = NM-4T
E0/0 = Router2 E0/0
S1/0 = Router3 S1/0
S1/1 = Router4 S1/1
`ROUTER Router2`
model = 3640
console = 2002
slot0 = NM-1E
slot1 = NM-4T
model = 3640
console = 2002
slot0 = NM-1E
slot1 = NM-4T
`ROUTER Router3`
model = 3640
console = 2003
slot0 = NM-1E
slot1 = NM-4T
model = 3640
console = 2003
slot0 = NM-1E
slot1 = NM-4T
`ROUTER Router4`
model = 3640
console = 2004
slot0 = NM-1E
slot1 = NM-4T
5.配置如下:
model = 3640
console = 2004
slot0 = NM-1E
slot1 = NM-4T
5.配置如下:
RouterA:
en
config t
host RouterA
inter e0/0
ip add 192.168.1.1 255.255.255.0
no shut
inter s1/0
ip add 192.168.2.1 255.255.255.0
no shut
inter s1/1
ip add 192.168.3.1 255.255.255.0
exit
router odr
config t
host RouterA
inter e0/0
ip add 192.168.1.1 255.255.255.0
no shut
inter s1/0
ip add 192.168.2.1 255.255.255.0
no shut
inter s1/1
ip add 192.168.3.1 255.255.255.0
exit
router odr
RouterB:
en
config t
host RouterB
inter e0/0
ip add 192.168.1.2 255.255.255.0
no shut
inter loopback 0
ip add 166.1.1.1 255.255.255.0
exit
RouterC:
config t
host RouterB
inter e0/0
ip add 192.168.1.2 255.255.255.0
no shut
inter loopback 0
ip add 166.1.1.1 255.255.255.0
exit
RouterC:
en
config t
host RouterC
inter s1/0
ip add 192.168.2.2 255.255.255.0
no shut
inter loopback 0
ip add 177.2.2.2 255.255.255.0
exit
RouterD:
config t
host RouterC
inter s1/0
ip add 192.168.2.2 255.255.255.0
no shut
inter loopback 0
ip add 177.2.2.2 255.255.255.0
exit
RouterD:
en
config t
host RouterD
inter s1/1
ip add 192.168.3.2 255.255.255.0
no shut
inter loopback 0
ip add 188.3.3.3 255.255.255.0
exit
6:验证结果
config t
host RouterD
inter s1/1
ip add 192.168.3.2 255.255.255.0
no shut
inter loopback 0
ip add 188.3.3.3 255.255.255.0
exit
6:验证结果
RouterA:
RouterA#show ip route
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
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
RouterA#show ip route
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
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
188.3.0.0/24 is subnetted, 1 subnets
o 188.3.3.0 [160/1] via 192.168.3.2, 00:00:49, Serial1/1
177.2.0.0/24 is subnetted, 1 subnets
o 177.2.2.0 [160/1] via 192.168.2.2, 00:00:13, Serial1/0
166.1.0.0/24 is subnetted, 1 subnets
o 166.1.1.0 [160/1] via 192.168.1.2, 00:00:01, Ethernet0/0
C 192.168.1.0/24 is directly connected, Ethernet0/0
C 192.168.2.0/24 is directly connected, Serial1/0
C 192.168.3.0/24 is directly connected, Serial1/1
RouterA#
o 188.3.3.0 [160/1] via 192.168.3.2, 00:00:49, Serial1/1
177.2.0.0/24 is subnetted, 1 subnets
o 177.2.2.0 [160/1] via 192.168.2.2, 00:00:13, Serial1/0
166.1.0.0/24 is subnetted, 1 subnets
o 166.1.1.0 [160/1] via 192.168.1.2, 00:00:01, Ethernet0/0
C 192.168.1.0/24 is directly connected, Ethernet0/0
C 192.168.2.0/24 is directly connected, Serial1/0
C 192.168.3.0/24 is directly connected, Serial1/1
RouterA#
RouterB:
RouterB#show ip route
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
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
RouterB#show ip route
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
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 192.168.1.1 to network 0.0.0.0
166.1.0.0/24 is subnetted, 1 subnets
C 166.1.1.0 is directly connected, Loopback0
C 192.168.1.0/24 is directly connected, Ethernet0/0
o* 0.0.0.0/0 [160/1] via 192.168.1.1, 00:00:17, Ethernet0/0
RouterB#
C 166.1.1.0 is directly connected, Loopback0
C 192.168.1.0/24 is directly connected, Ethernet0/0
o* 0.0.0.0/0 [160/1] via 192.168.1.1, 00:00:17, Ethernet0/0
RouterB#
RouterC:
RouterC#show ip route
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
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
RouterC#show ip route
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
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 192.168.2.1 to network 0.0.0.0
177.2.0.0/24 is subnetted, 1 subnets
C 177.2.2.0 is directly connected, Loopback0
C 192.168.2.0/24 is directly connected, Serial1/0
o* 0.0.0.0/0 [160/1] via 192.168.2.1, 00:00:22, Serial1/0
RouterC#
C 177.2.2.0 is directly connected, Loopback0
C 192.168.2.0/24 is directly connected, Serial1/0
o* 0.0.0.0/0 [160/1] via 192.168.2.1, 00:00:22, Serial1/0
RouterC#
RouterD:
RouterD#
RouterD#show ip route
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
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
RouterD#show ip route
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
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 192.168.3.1 to network 0.0.0.0
188.3.0.0/24 is subnetted, 1 subnets
C 188.3.3.0 is directly connected, Loopback0
C 192.168.3.0/24 is directly connected, Serial1/1
o* 0.0.0.0/0 [160/1] via 192.168.3.1, 00:00:26, Serial1/1
RouterD#
C 188.3.3.0 is directly connected, Loopback0
C 192.168.3.0/24 is directly connected, Serial1/1
o* 0.0.0.0/0 [160/1] via 192.168.3.1, 00:00:26, Serial1/1
RouterD#
OVER!
