当使用PBR匹配ACL时，ACL当中不应当匹配源端口，GSR无法使用硬件处理该任务。这样会触发进程交换（Process Switching），导致GSR的CPU性能降格（degrade）。
见《Implementing Access Lists on Cisco 12000 Series Internet Routers》
Note: When you configure policy-based routing (PBR) with match statements to match ACLs, the ACLs should not match the source port. The gigabit switch router (GSR) does not support hardware switching for the PBR with ACLs that match the source port. It triggers process switching and GSR performance degrades.
