"RouterA和RouterB之间运行OSPF路由协议,RouterB通过import-route static引入172.1.17.0、172.1.18.0、172.1.19.0、172.1.20.0四条路由,且通过如下命令进行过滤: [~RouterB]ip ip-prefix a2b index 10 permit 172.1.17.0 24[~RouterB]ip ip-prefix a2b index 20 permit 172.1.18.0 24
[~RouterB]ip ip-prefix a2b index 30 permit 172.1.19.0 24
[~RouterB]ospf
[~RouterB-ospf-1]filter-policy ip-prefix a2b export
[~RouterB-ospf-1]commit
以下描述中,正确的是哪一项?"