此问题可能是由于帧中继链路的拥塞造成的 
使用 show interface serial 来检查广播队列的DROP数目 
Serial0 is up, line protocol is up 
Hardware is MK5025 
Description: Charlotte Frame Relay Port DLCI 100 
MTU 1500 bytes, BW 1024 Kbit, DLY 20000 usec, 
reliability 255/255, txload 44/255, rxload 44/255 
Encapsulation FRAME-RELAY, loopback not set, keepalive set (10 sec) 
LMI enq sent 7940, LMI stat recvd 7937, LMI upd recvd 0, DTE LMI up 
LMI enq recvd 0, LMI stat sent 0, LMI upd sent 0 
LMI DLCI 1023 LMI type is CISCO frame relay DTE 
Broadcast queue 64/64, broadcasts sent/dropped 1769202/1849660, interface broadcasts 3579215 
由此看出,链路有拥塞了. 
使用frame-relay broadcast-queue 255  96000 160 解决问题 

from:http://www.cnblogs.com/cunshen/articles/124462.html