Você está correto em dizer que a entrada * na coluna Gateway significa que o pacote é mantido na rede local.
Na coluna Flags , o U significa que a rota está ativa, enquanto o G significa que a rota é para um gateway.
Outras opções que podem aparecer na coluna Flags são:
U : This flag signifies that the route is up
G : This flag signifies that the route is to a gateway. If this flag is not present then we can say that the route is to a directly connected destination
H : This flag signifies that the route is to a host which means that the destination is a complete host address. If this flag is not present then it can be assumed that the route is to a network and destination would be a network address.
D : This flag signifies that this route is created by a redirect.
M : This flag signifies that this route is modified by a redirect.
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