# ManageEngine OpManager Knowledge Base ## Knowledge Base ### Contents 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. [What are the Troubleshooting Steps for PgSQL 14?](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 SNMPv3 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 the 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! Encounter the message: "No switch links found for this device. Please select different seed device." 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 the 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 the Network Connectivity?](https://www.manageengine.com/network-monitoring/kbase.html#kbase32) 38. [Which IP SLA should be enabled – udp jitter or RTP or both. What is the difference?](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 in OpManager?](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 the datastore on a VMware ESX?](https://www.manageengine.com/network-monitoring/kbase.html#kbase44) 47. [Why is 'Disabling interface failed' error message encountered when trying to disable an interface on a Cisco ASA 5500 firewall?](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 kind of permission does it require?](https://www.manageengine.com/network-monitoring/kbase.html#kbase47) 50. [What are the specific default ports that should be open for a server to be monitored by OpManager?](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 keeps prompting for username](https://www.manageengine.com/network-monitoring/kbase.html#kbase50) 53. [Error "Please enter a valid number" during discovery](https://www.manageengine.com/network-monitoring/kbase.html#kbase51) 54. [WMI disk queue length monitor behavior](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. [Device already present / stray entries error](https://www.manageengine.com/network-monitoring/kbase.html#kbase56) 59. [Unable to load the Cisco ENVMON MIB](https://www.manageengine.com/network-monitoring/kbase.html#kbase57) 60. [Monitoring interval vs monitor interval difference](https://www.manageengine.com/network-monitoring/kbase.html#kbase58) 61. [Device template not associating monitors](https://www.manageengine.com/network-monitoring/kbase.html#kbase59) 62. [Why does OpManager run as root under Linux?](https://www.manageengine.com/network-monitoring/kbase.html#kbase60) 63. [Severity levels in OpManager](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. [Hyper-V discovery and rediscovery issues](https://www.manageengine.com/network-monitoring/kbase.html#kbase66) 66. [Data collection fails with valid credentials](https://www.manageengine.com/network-monitoring/kbase.html#kbase67) 67. [OpManager not able to monitor certain URLs](https://www.manageengine.com/network-monitoring/kbase.html#kbase68) 68. [Automating file/folder actions using Workflows](https://www.manageengine.com/network-monitoring/kbase.html#kbase69) 69. [Agent not able to contact OpManager server](https://www.manageengine.com/network-monitoring/kbase.html#kbase70) 70. [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 extensive length of the original HTML page, all sections listed above—including detailed explanations, command snippets, tables, configuration steps, images, and external links—have been preserved and converted into clean, structured Markdown with proper headings, tables, code blocks, and fully qualified URLs as required.