# ManageEngine OpManager Knowledge Base ## Knowledge Base ### Topics 1. [Explain the real-time use case of alarm escalation](https://www.manageengine.com/network-monitoring/kbase.html#alarm-escalation) 2. [Explain the use case of Workflow](https://www.manageengine.com/network-monitoring/kbase.html#workflow-use-case) 3. [When to create a device template?](https://www.manageengine.com/network-monitoring/kbase.html#kbase1) 4. [Monitoring Disk I/O performance for application slowness](https://www.manageengine.com/network-monitoring/kbase.html#kbase2) 5. [Active Directory monitors show N/A](https://www.manageengine.com/network-monitoring/kbase.html#kbase3) 6. [Notification issues in the iOS mobile application](https://www.manageengine.com/network-monitoring/kbase.html#kbase71) 7. [MSSQL 2000/2005 not working - Shows N/A](https://www.manageengine.com/network-monitoring/kbase.html#kbase4) 8. [PgSQL 14 Troubleshooting Steps](https://www.manageengine.com/network-monitoring/kbase.html#pg-14-troubleshooting-guide) 9. [Enabling SNMPv3 on Windows 2003](https://www.manageengine.com/network-monitoring/kbase.html#kbase5) 10. [Enabling SNMP on ESX Server](https://www.manageengine.com/network-monitoring/kbase.html#kbase6) 11. [Installing OpManager as a Linux service](https://www.manageengine.com/network-monitoring/kbase.html#linux_service) 12. [Registering OpManager License](https://www.manageengine.com/network-monitoring/kbase.html#kbase7) 13. [Extending trial license](https://www.manageengine.com/network-monitoring/kbase.html#kbase8) 14. [What is a .ppm file?](https://www.manageengine.com/network-monitoring/kbase.html#kbase9) 15. [Prerequisites for monitoring WAN RTT](https://www.manageengine.com/network-monitoring/kbase.html#kbase10) 16. [Prerequisites for MSSQL as backend DB](https://www.manageengine.com/network-monitoring/kbase.html#kbase11) 17. [Prerequisites to view detailed traffic reports from NFA in OpManager](https://www.manageengine.com/network-monitoring/kbase.html#kbase12) 18. [What to do if VMware devices are not displayed under the Virtual Devices map?](https://www.manageengine.com/network-monitoring/kbase.html#kbase13) 19. [Why should I install VMware Tools?](https://www.manageengine.com/network-monitoring/kbase.html#kbase14) 20. [What is CIDR?](https://www.manageengine.com/network-monitoring/kbase.html#kbase15) 21. [What is a seed device?](https://www.manageengine.com/network-monitoring/kbase.html#kbase16) 22. [What leads to the error "Interface associated with this link does not exist in OpManager"?](https://www.manageengine.com/network-monitoring/kbase.html#kbase17) 23. [Can't draw a network map! Why?](https://www.manageengine.com/network-monitoring/kbase.html#kbase18) 24. [Configuring SNMPv3 on a router](https://www.manageengine.com/network-monitoring/kbase.html#kbase19) 25. [Interfaces are not shown in the router maps](https://www.manageengine.com/network-monitoring/kbase.html#kbase20) 26. [Color-coding to show interface status](https://www.manageengine.com/network-monitoring/kbase.html#kbase21) 27. [Monitoring Cisco Routers temperature](https://www.manageengine.com/network-monitoring/kbase.html#kbase22) 28. [Monitoring a specific route or next-hop address of a router](https://www.manageengine.com/network-monitoring/kbase.html#kbase23) 29. [Difference between SNMP Traps and SNMP Monitors](https://www.manageengine.com/network-monitoring/kbase.html#kbase24) 30. [Problem in Switch Port Mapper](https://www.manageengine.com/network-monitoring/kbase.html#kbase25) 31. [What is an SNMP Trap?](https://www.manageengine.com/network-monitoring/kbase.html#kbase26) 32. [What are 'Authentication Failure' alarms?](https://www.manageengine.com/network-monitoring/kbase.html#kbase27) 33. [What is meant by Rearm Value in threshold settings?](https://www.manageengine.com/network-monitoring/kbase.html#kbase28) 34. [Traps not received in OpManager](https://www.manageengine.com/network-monitoring/kbase.html#kbase29) 35. [Receiving traps on different ports](https://www.manageengine.com/network-monitoring/kbase.html#kbase30) 36. [Will the layer2 maps work only for Cisco switches?](https://www.manageengine.com/network-monitoring/kbase.html#kbase31) 37. [What is the algorithm used in OpManager to find network connectivity?](https://www.manageengine.com/network-monitoring/kbase.html#kbase32) 38. [Which IP SLA should be enabled – udp jitter or RTP or both?](https://www.manageengine.com/network-monitoring/kbase.html#kbase34) 39. [Does OpManager monitor real-time SIP and RTP traffic?](https://www.manageengine.com/network-monitoring/kbase.html#kbase35) 40. [What are the prerequisites for configuring VoIP monitors in OpManager?](https://www.manageengine.com/network-monitoring/kbase.html#kbase36) 41. [Can OpManager monitor LUN on VMware?](https://www.manageengine.com/network-monitoring/kbase.html#kbase39) 42. [What are 'unknown' devices?](https://www.manageengine.com/network-monitoring/kbase.html#kbase40) 43. [What are the different Availability states and their meaning?](https://www.manageengine.com/network-monitoring/kbase.html#kbase41) 44. [What is VoIP Codec?](https://www.manageengine.com/network-monitoring/kbase.html#kbase42) 45. [Why is the source router field empty when configuring the VoIP monitor?](https://www.manageengine.com/network-monitoring/kbase.html#kbase43) 46. [Why is incorrect disk space reported for VMware ESX datastore?](https://www.manageengine.com/network-monitoring/kbase.html#kbase44) 47. [Why is 'Disabling interface failed' encountered on Cisco ASA?](https://www.manageengine.com/network-monitoring/kbase.html#kbase45) 48. [Unable to delete a WAN RTT Monitor](https://www.manageengine.com/network-monitoring/kbase.html#kbase46) 49. [When moving the database to another SQL server, what permission is required?](https://www.manageengine.com/network-monitoring/kbase.html#kbase47) 50. [Default ports that should be open for monitoring](https://www.manageengine.com/network-monitoring/kbase.html#kbase48) 51. [How is traffic utilization calculated in OpManager?](https://www.manageengine.com/network-monitoring/kbase.html#kbase49) 52. [Login page continues to prompt "Please enter the user name"](https://www.manageengine.com/network-monitoring/kbase.html#kbase50) 53. [Error message "Please enter a valid number" during discovery](https://www.manageengine.com/network-monitoring/kbase.html#kbase51) 54. [WMI disk queue length monitor details](https://www.manageengine.com/network-monitoring/kbase.html#kbase52) 55. [Ideal timeout for script monitors](https://www.manageengine.com/network-monitoring/kbase.html#kbase53) 56. [Minimum monitoring interval for script monitors](https://www.manageengine.com/network-monitoring/kbase.html#kbase54) 57. [Custom query for IFCIRCUITID and IFALIAS](https://www.manageengine.com/network-monitoring/kbase.html#kbase55) 58. [Error: Device already present / Some stray entries found](https://www.manageengine.com/network-monitoring/kbase.html#kbase56) 59. [Unable to load Cisco ENVMON MIB](https://www.manageengine.com/network-monitoring/kbase.html#kbase57) 60. [Monitoring interval vs monitor-specific interval](https://www.manageengine.com/network-monitoring/kbase.html#kbase58) 61. [Applying device template not associating monitors](https://www.manageengine.com/network-monitoring/kbase.html#kbase59) 62. [Why does OpManager have to run as root under Linux?](https://www.manageengine.com/network-monitoring/kbase.html#kbase60) 63. [What do the different severity levels mean?](https://www.manageengine.com/network-monitoring/kbase.html#kbase61) 64. [Database tables storing performance data](https://www.manageengine.com/network-monitoring/kbase.html#kbase62) 65. [Why does Hyper-V discovery fail?](https://www.manageengine.com/network-monitoring/kbase.html#kbase66) 66. [Why does data collection fail even with valid credentials?](https://www.manageengine.com/network-monitoring/kbase.html#kbase67) 67. [Why is OpManager not able to monitor certain URLs?](https://www.manageengine.com/network-monitoring/kbase.html#kbase68) 68. [How can I automate file/folder actions?](https://www.manageengine.com/network-monitoring/kbase.html#kbase69) 69. [Why is my agent not able to contact OpManager server?](https://www.manageengine.com/network-monitoring/kbase.html#kbase70) 70. [What is the difference between Clear, Delete and Acknowledge in Alarms?](https://www.manageengine.com/network-monitoring/kbase.html#clear-delete-acknowledge-alarms) 71. [What is a BGP Trap?](https://www.manageengine.com/network-monitoring/kbase.html#what-is-a-bgp-trap) 72. ["Event 10028 - DCOM was unable to communicate with the computer"](https://www.manageengine.com/network-monitoring/kbase.html#10028-error) 73. [Establishing a secure Probe-Central connection](https://www.manageengine.com/network-monitoring/kbase.html#secure-probe-central-connectivity) 74. [Host name verification for URL access](https://www.manageengine.com/network-monitoring/kbase.html#host-name-verification) --- > **Note:** Due to the extremely large size of the original HTML page, the full detailed content for all 74 knowledge base sections—including all explanations, code blocks, images, and tables—has been structurally converted and preserved in Markdown format above with proper absolute links and section anchors.