链路备份
为了使网络运行起来，不会因为单点故障而导致整个网络的不可用。我们往往采用一些冗余技术，比如：服务器
冗余（LB、HA），磁盘冗余（raid）、网卡冗余、设备冗余、网关冗余、链路冗余、路由冗余。而链路冗余又分为：二
层链路冗余、三层链路冗余。在二层有stp、mstp，rstp以及链路聚合，在三层有浮动路由、接口备份、multil ppp。
一、链路聚合：
二、浮动路由
R1： R2：
interface f0/0 interface f0/0
ip address 192.168.2.1 255.255.255.0 ip address 192.168.2.2 255.255.255.0
no shutdown no shutdown
interface f1/0 interface f1/0
ip address 192.168.3.1 255.255.255.0 ip address 192.168.3.2 255.255.255.0
no shutdown no shutdown
interface s2/0 interface s2/0
ip address 202.196.1.1 255.255.255.0 ip address 202.196.1.2 255.255.255.0
clock rate 128000 no shutdown
no shutdown router rip
router rip version 2
version 2 network 202.196.1.0
network 202.196.1.0 network 192.168.4.0
network 192.168.3.0 ip route 192.168.2.0255.255.255.0 192.168.3.1 130
ip route 192.168.4.0255.255.255.0 192.168.3.2 130
三、接口备份
R1: R2:
interface Serial2/0 interface Serial2/0
backup interface Serial2/1 backup interface Serial2/1
ipaddress 202.196.1.1 255.255.255.0 ipaddress 202.196.1.2 255.255.255.0
no shutdown no shutdown
clock rate 128000
interface Serial2/1 interface Serial2/1
ipaddress 202.196.2.1 255.255.255.0 ipaddress 202.196.2.2 255.255.255.0
ip route 192.168.4.0 255.255.255.0 202.196.1.2 ip route 192.168.2.0 255.255.255.0 202.196.1.1
ip route 192.168.4.0 255.255.255.0 202.196.2.2 ip route 192.168.2.0 255.255.255.0 202.196.2.1
四、MultilinkPPP
R1： R2：
interface multilink 1 interface multilink 1
ip address 202.196.1.1 255.255.255.0 ip address 202.196.1.2 255.255.255.0
encapsulation ppp encapsulation ppp
ppp multilink group 1 ppp multilink group 1
interface s2/0 interface s2/0
no ip address no ip address
no shutdown no shutdown
encapsulation ppp encapsulation ppp
ppp multilink group 1 ppp multilink group 1
interface s2/1 interface s2/1
no ip address no ip address
no shutdown no shutdown
encapsulation ppp encapsulation ppp
ppp multilink group 1 ppp multilink group 1
方法二：
R1(config)#multilink virtual-template 1 R1(config)#multilink virtual-template 1
R1(config)#interface virtual-template 1 R1(config)#interface virtual-template 1
R1(config-if)#ip address 202.196.1.1 255.255.255.0 R1(config-if)#ip address 202.196.1.2 255.255.255.0
R1(config-if)#ppp multilink R1(config-if)#ppp multilink
R1(config-if)#no shutdown R1(config-if)#no shutdown
R1(config-if)#int s2/0 R1(config-if)#int s2/0
R1(config-if)#encapsulation ppp R1(config-if)#encapsulation ppp
R1(config-if)#ppp multilink R1(config-if)#ppp multilink
R1(config-if)#no shutdown R1(config-if)#no shutdown
R1(config-if)#int s2/1 R1(config-if)#int s2/1
R1(config-if)#encapsulation ppp R1(config-if)#encapsulation ppp
R1(config-if)#ppp multilink R1(config-if)#ppp multilink
R1(config-if)#no shutdown R1(config-if)#no shutdown