动态路由ospf里
cost是用来设置动态路由优先级的，比如R1到R2有两条路可走，cost低的，路由优先走这条路，cost一样的话，就负载均衡，两条路都走；
priority是用来选班长和副班长用的，priority高的优先级就高，更可能选上班长。否则ospf会自动选择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.