多项选择题 To protect against first-hop router failure， four protocols were developed to ensure IP routing  redundancy.  Which of the following are they？（）

多项选择题 HSRP is being set up between two Company devices.  In what three states is it possible for an  HSRP router to be in？（）

多项选择题 R1 and R2 exchange HSRP between each other in the Company network.  In which three HSRP  states do routers send hello messages？（）