为ISR路由器上的双ISP故障切换配置“ip dhcp client route track”

简介

本文档介绍在思科集成服务路由器(ISR)2900系列上使用DHCP配置双ISP故障切换的过程。

先决条件

要求

本文档没有任何特定的要求。

使用的组件

本文档不限于特定的软件和硬件版本。

本文档中的信息都是基于特定实验室环境中的设备编写的。本文档中使用的所有设备最初均采用原始（默认）配置。如果您使用的是真实网络，请确保您已经了解所有命令的潜在影响。

配置

网络图

配置

当路由器上有两个ISP端点，并且都通过DHCP从ISP获取IP地址时，此设置非常有用。

CLIENT#sh ip int b 

Interface IP-Address OK? Method Status Protocol
Embedded-Service-Engine0/0 unassigned YES NVRAM administratively down down 
GigabitEthernet0/0 10.106.38.136 YES DHCP up up 
GigabitEthernet0/1 unassigned YES NVRAM up up 
GigabitEthernet0/1.100 1.1.1.4 YES DHCP up up 
GigabitEthernet0/1.200 2.2.2.4 YES DHCP up up 
GigabitEthernet0/2 unassigned YES NVRAM down down 
Loopback0 11.11.11.11 YES NVRAM up up 

interface gigabitethernet 0/1.100和interface gigabitethernet 0/1.200是两个接口，分别从两个ISP获取dhcp ip地址。

interface gigabitethernet 0/1.100为主接口，interface gigabitethernet 0/1.200为辅助接口。

静态路由配置： 

具有更高AD值的辅助路由：

ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/1.200 dhcp 200
ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/1.100 dhcp

接口配置: 

CLIENT#sh run int GigabitEthernet0/1.100
Building configuration...

Current configuration : 112 bytes
!
interface GigabitEthernet0/1.100
 encapsulation dot1Q 100
 ip dhcp client route track 2         
 ip address dhcp
end

注意：在接口上发出ip address dhcp命令之前，必须配置ip dhcp client命令。仅当从DHCP获取IP地址时，才会检查ip dhcp client命令。如果在从DHCP获取IP地址后发出ip dhcp client命令，则直到路由器下一次从DHCP获取IP地址时才会生效。

CLIENT#sh run int GigabitEthernet0/1.200
Building configuration...

Current configuration : 82 bytes
!
interface GigabitEthernet0/1.200
 encapsulation dot1Q 200
 ip address dhcp
end

IP服务级别协议(SLA):跟踪路由来源主接口： 

CLIENT#sh run | sec ip sla
track 2 ip sla 2 reachability
ip sla 2
 icmp-echo 11.11.11.11 source-interface GigabitEthernet0/1.100
ip sla schedule 2 life forever start-time now
ip sla auto discovery

CLIENT#sh ip route

C 1.1.1.0/24 is directly connected, GigabitEthernet0/1.100
L 1.1.1.4/32 is directly connected, GigabitEthernet0/1.100
 2.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 2.2.2.0/24 is directly connected, GigabitEthernet0/1.200
L 2.2.2.4/32 is directly connected, GigabitEthernet0/1.200

验证

使用本部分可确认配置能否正常运行。

当跟踪启动时，默认网关将路由指向主路由： 

CLIENT#sh ip route track-table 
 ip route 0.0.0.0 0.0.0.0 1.1.1.1 254 track 2 state is [up]
 ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/1.100 1.1.1.1 track 2 state is [up]

CLIENT#sh ip route

Codes: L - local, C - connected, S - static, 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

       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, H - NHRP, l - LISP

       + - replicated route, % - next hop override



Gateway of last resort is 1.1.1.1 to network 0.0.0.0



S*    0.0.0.0/0 [1/0] via 1.1.1.1, GigabitEthernet0/1.100

      1.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C        1.1.1.0/24 is directly connected, GigabitEthernet0/1.100

L        1.1.1.5/32 is directly connected, GigabitEthernet0/1.100

      2.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C        2.2.2.0/24 is directly connected, GigabitEthernet0/1.200

L        2.2.2.4/32 is directly connected, GigabitEthernet0/1.200

当路径断开时，默认网关将路由指向辅助路由：

CLIENT#sh ip route track-table 

 ip route 0.0.0.0 0.0.0.0 1.1.1.1 254 track 2 state is [down]

 ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/1.100 1.1.1.1 track 2 state is [down]


CLIENT#sh ip route

Codes: L - local, C - connected, S - static, 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

       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, H - NHRP, l - LISP

       + - replicated route, % - next hop override



Gateway of last resort is 2.2.2.1 to network 0.0.0.0



S*    0.0.0.0/0 [200/0] via 2.2.2.1, GigabitEthernet0/1.200

      1.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C        1.1.1.0/24 is directly connected, GigabitEthernet0/1.100

L        1.1.1.5/32 is directly connected, GigabitEthernet0/1.100

      2.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C        2.2.2.0/24 is directly connected, GigabitEthernet0/1.200

L        2.2.2.4/32 is directly connected, GigabitEthernet0/1.200

      10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C        10.106.38.0/24 is directly connected, GigabitEthernet0/0

L        10.106.38.136/32 is directly connected, GigabitEthernet0/0

故障排除

目前没有针对此配置的故障排除信息。