I want to monitor the delay of Cisco router interface through ZABBIX. 

1.Query the OID value of IP SLA monitoring 

2.Build the RTT Mon Template,which can auto discorvey the items

3.Link the Template to a Host(a Cisco Router)

After the before steps, the Items have been found correctly ，but the delay value is 0 always.

I check the OID of the item in the Host by command line (snmpwalk )，which can correctly obtain the delay value.

 I don't know why, and please help me find mistakes.