U Up: The route is active. H Host: The route destination is a single host. G Gateway: Send anything for this destination on to this remote system, which will figure out from there where to send it.
S Static: This route was configured manually, not automatically generated by the system. C Clone: Generates a new route based upon this route for machines we connect to. This type of route is normally used for local networks. W WasCloned: Indicated a route that was auto-configured based upon a local area network (Clone) route. L Link: Route involves references to Ethernet hardware.
R (reinstate route for dynamic routing) D (dynamically installed by daemon or redirect) M (modified from routing daemon or redirect) A (installed by addrconf) C (cache entry) ! (reject route)
FreeBSD里常看到的是UC, UHLW, UGS, UGHS这几种。UC根据本地网络配置自动生成的，UHLW是由UC根据连接情况自动生成的，UGS是手工配置的段网关路由，UGHS是手工配置的主机网关路由。
Linux里常看到的是U, UG, UGH这几种。U和BSD的UC是一样的，UG和UGS一样，UGH和UGHS一样，没有UHLW。