单选题How often are IS-IS Hello packets transmitted?（）A 3 seconds for DIS; 9 seconds for non-DISB 9 seconds for DIS; 3 seconds for non-DISC 10 seconds for DIS; 3 seconds for non-DISD 10 seconds for all routers
题目
单选题
How often are IS-IS Hello packets transmitted?（）
A
3 seconds for DIS; 9 seconds for non-DIS
B
9 seconds for DIS; 3 seconds for non-DIS
C
10 seconds for DIS; 3 seconds for non-DIS
D
10 seconds for all routers