命令：area transit-area-id virtual-link router-id

area transit-area-id virtual-link router-id transmit-delay 1-8192
area transit-area-id virtual-link router-id retransmit-interval 1-8192
area transit-area-id virtual-link router-id hello-interval 1-8192
area transit-area-id virtual-link router-id dead-interval 1-8192


推荐dead-interval还是hello-interval的4倍关系

默认虚链路上邻居（子到主区域，主到主区域）HELLO都是10 DEAD都是40
transmit-delay默认是1 retransmit-interval默认是5