配置实现：
偶数
access-list 90 permit 0.0.0.0 0.0.0.254
奇数
access-list 91 permit 0.0.0.1 0.0.0.254
route-map Route_Policy permit 10
match ip address 90
set ip default next-hop 202.123.123.2
route-map Route_Policy permit 20
match ip address 91
set ip default next-hop 202.123.123.1
interface FastEthernet0/1
ip policy route-map Route_Policy