動態路由ospf里
cost是用來設置動態路由優先級的，比如R1到R2有兩條路可走，cost低的，路由優先走這條路，cost一樣的話，就負載均衡，兩條路都走；
priority是用來選班長和副班長用的，priority高的優先級就高，更可能選上班長。否則ospf會自動選擇DR和BDR。
router's priority. Used to determine the designated router in a broadcast network. The router with highest priority value takes precedence. Priority value 0 means the router is not eligible to become designated or backup designated router at all.