一 网络拓扑如上图R2有2个出口一个是固定ip配置默认路由一个dhcp自动获取。发现固定ip接口的默认路由不生效需用户希望解决该问题。二 设备配置1.1 R1设备配置hostname R1!service dhcp!ip dhcp pool 203.1.1.2network 203.1.1.0 255.255.255.0default-router 203.1.1.2!interface GigabitEthernet 0/0ip address 202.1.1.2 255.255.255.0!interface GigabitEthernet 0/1ip address 203.1.1.2 255.255.255.0!interface Loopback 0ip address 8.8.8.8 255.255.255.255!1.2 R2设备配置hostname R2!ip access-list extended 10010 permit ip any any!ip access-list extended 10110 permit ip any any!interface GigabitEthernet 0/0ip address 202.1.1.1 255.255.255.0ip nat outside!interface GigabitEthernet 0/1ip address dhcpip nat outside!interface GigabitEthernet 0/2ip address 1.1.1.2 255.255.255.0ip nat inside!ip nat inside source list 100 interface GigabitEthernet 0/0 overloadip nat inside source list 101 interface GigabitEthernet 0/1 overload!ip route 0.0.0.0 0.0.0.0 202.1.1.2ip route 192.168.1.1 255.255.255.255 1.1.1.1!1.3 R3设备配置hostname R3!interface GigabitEthernet 0/0ip address 1.1.1.1 255.255.255.0!interface Loopback 0ip address 192.168.1.1 255.255.255.255!ip route 0.0.0.0 0.0.0.0 1.1.1.2!二 路由查看2.1 R2查看路由表出口为dhcp接口R2路由器查看路由表非固定IP地址路由而是来自于DHCP分配的地址R2#show ip routeCodes: C - Connected, L - Local, S - StaticR - RIP, O - OSPF, B - BGP, I - IS-IS, V - Overflow routeN1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2E1 - OSPF external type 1, E2 - OSPF external type 2SU - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2IA - Inter area, EV - BGP EVPN, A - Arp to hostLA - Local aggregate route* - candidate defaultGateway of last resort is 202.1.1.2 to network 0.0.0.0S* 0.0.0.0/0 [1/0] via 202.1.1.2C 1.1.1.0/24 is directly connected, GigabitEthernet 0/2C 1.1.1.2/32 is local host.S 192.168.1.1/32 [1/0] via 1.1.1.1C 202.1.1.0/24 is directly connected, GigabitEthernet 0/0C 202.1.1.1/32 is local host.C 203.1.1.0/24 is directly connected, GigabitEthernet 0/1C 203.1.1.1/32 is local host.R2#三 业务测试R3#ping 8.8.8.8 source 192.168.1.1Sending 5, 100-byte ICMP Echoes to 8.8.8.8, timeout is 2 seconds: press CtrlC to break !!!!!Success rate is 100 percent (5/5), round-trip min/avg/max 1/3/8 ms.R3#四 解决方法-关闭dhcp下发默认路由功能4.1 R2 dhcp自动获取接口配置dhcp force-no-routehostname R2!interface GigabitEthernet 0/1ip address dhcpip address dhcp force-no-routeip nat outside!4.2 R2再次查看路由表正常R2#show ip routeCodes: C - Connected, L - Local, S - StaticR - RIP, O - OSPF, B - BGP, I - IS-IS, V - Overflow routeN1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2E1 - OSPF external type 1, E2 - OSPF external type 2SU - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2IA - Inter area, EV - BGP EVPN, A - Arp to hostLA - Local aggregate route* - candidate defaultGateway of last resort is 201.1.1.2 to network 0.0.0.0S* 0.0.0.0/0 [1/0] via 201.1.1.2C 1.1.1.0/24 is directly connected, GigabitEthernet 0/2C 1.1.1.2/32 is local host.S 192.168.1.1/32 [1/0] via 1.1.1.1C 202.1.1.0/24 is directly connected, GigabitEthernet 0/0C 202.1.1.1/32 is local host.C 203.1.1.0/24 is directly connected, GigabitEthernet 0/1C 203.1.1.1/32 is local host.R2#五 最后总结当固定ip地址手工配置静态路由优先级为1与dhcp自动获取的默认路由同时存在的时候dhcp下发的默认路由优先级最高将导致手工配置静态路由优先级无法生效需要禁用dhcp下发默认路由功能ip address dhcp force-no-route。禁止dhcp下发默认路由功能不同设备可能支持情况不一样要以实际设备命令为准有些设备可能不支持该功能或者命令。另外友商设备下发到设备的默认路由一般优先级为70