单项选择题 Which type of router cannot exist within a stub area?（）

单项选择题 Which OSPF area type allows for the flooding of a Type 7 LSA?（）

单项选择题 An OSPF non-backbone area allows external routes to be flooded within the area. These external routes are propagated into the backbone. However, external routes from other areas are not allowed to enter this area. Which type of OSPF area does this describe?（）