Troubleshooting call forwarding that fails in Unified CM

See also

Sources

1. 1
   Call Back cannot be activated against a line that forwards all calls to the voicemail system.

   Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Restrictions · Checked 2026-10-02
2. 2
   With Activating Device/Line CSS, Unified CM populates the primary CFA CSS with the line CSS and the secondary CFA CSS with the activating device's CSS when CFA is activated.

   Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forward All, Including CFA Loop Prevention and CFA Loop Breakout; CFA CSS Activation Policy · Checked 2026-10-02
3. 3
   Unified CM concatenates the primary CFA CSS and the secondary CFA CSS (primary first) to validate the CFA destination and to route the forwarded call.

   Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Fields; Secondary Calling Search Space for Forward All · Checked 2026-10-02
4. 4
   With Configured CSS, the primary and secondary Call Forward All calling search spaces configured on the directory number control both CFA activation and the forwarded call.

   Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forward All, Including CFA Loop Prevention and CFA Loop Breakout; CFA CSS Activation Policy · Checked 2026-10-02
5. 5
   When a directory number's Calling Search Space Activation Policy is Use System Default, Unified CM uses the clusterwide CFA CSS Activation Policy service parameter to decide which CSS governs Call Forward All.

   Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Directory Number Configuration Fields for Call Forwarding; Calling Search Space Activation Policy · Checked 2026-10-02
6. 6
   The Directory Number Configuration window in Unified CM has a Calling Search Space Activation Policy field for Call Forward All with three values: Use System Default, With Configured CSS, and With Activating Device/Line CSS.

   Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Directory Number Configuration Fields for Call Forwarding; Calling Search Space Activation Policy · Checked 2026-10-02
7. 7
   The CFA CSS Activation Policy service parameter, set under System > Service Parameters, takes one of two values: With Configured CSS or With Activating Device/Line CSS.

   Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forward All, Including CFA Loop Prevention and CFA Loop Breakout; CFA CSS Activation Policy · Checked 2026-10-02
8. 8
   The Forward All Calling Search Space is used to validate the destination a user enters when activating Call Forward All from the phone.

   Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Fields; Forward All Calling Search Space · Checked 2026-10-02
9. 9
   When the CFA Destination Override service parameter is True, Unified CM ignores a line's CFA when the call comes from the CFA destination itself, so that party can reach the forwarded user.

   Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Enable Destination Override for Call Forwarding · Checked 2026-10-02
10. 10
    CFA Destination Override works only when the calling party number has not been transformed, because a transformed number no longer matches the CFA destination.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Enable Destination Override for Call Forwarding · Checked 2026-10-02
11. 11
    On the phone, the message showing that Call Forward All is active takes priority over the Do Not Disturb indication.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Interactions; Do Not Disturb · Checked 2026-10-02
12. 12
    Cisco documents that 7940 and 7960 SIP phones logged in to hunt groups with CFA active are skipped and the next line group member rings, whereas some other SIP phone models (such as 7911, 7941 and 7961) are still presented the call.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Interactions; hunt group note on 7940/7960 SIP phones · Checked 2026-10-02
13. 13
    Immediate Divert is not supported on a line where Call Forward All or Call Forward Busy is active.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Interactions; Immediate Divert · Checked 2026-10-02
14. 14
    Intercom calls cannot be forwarded in Unified CM.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Restrictions · Checked 2026-10-02
15. 15
    With CFA loop breakout, a call that hits a CFA loop goes through the forwarding chain and stops at the phone where the loop is identified, which rings; if that phone also has CFNA set, the call follows CFNA when the No Answer Ring Duration expires.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forward All, Including CFA Loop Prevention and CFA Loop Breakout; loop breakout example 1000-1001-1002 with CFNA to 1004 · Checked 2026-10-02
16. 16
    If the same directory number exists in different partitions, Unified CM allows CFA activation even though the forwarding chain could otherwise look like a loop.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forward All, Including CFA Loop Prevention and CFA Loop Breakout · Checked 2026-10-02
17. 17
    Unified CM does not prevent a CFA loop when Call Forward All is set from Unified CM Administration or from the Self Care Portal rather than from the phone.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Restrictions · Checked 2026-10-02
18. 18
    CFA loop prevention applies only when CFA is activated from the phone, when the hop count of the CFA chain exceeds the Forward Maximum Hop Count service parameter, and when every phone in the chain has CFA (not CFB, CFNA or another forward type) active.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forward All, Including CFA Loop Prevention and CFA Loop Breakout · Checked 2026-10-02
19. 19
    Unified CM refuses CFA activation on the phone when it identifies a Call Forward All loop; in Cisco's example, 1000 cannot forward to 1001 when 1001, 1002 and 1003 already forward all calls back around to 1000.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forward All, Including CFA Loop Prevention and CFA Loop Breakout · Checked 2026-10-02
20. 20
    For MLPP calls, CFA needs a Multilevel Administrator (MAP) target configured; if none is set, the call is rejected with reorder tone.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Restrictions; MLPP · Checked 2026-10-02
21. 21
    When the Voice Mail check box is checked for a forwarding type, Unified CM ignores that type's Destination and Calling Search Space fields and uses the settings from the Voice Mail Profile Configuration window.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Fields; Voice Mail check box · Checked 2026-10-02
22. 22
    The Call Forward Busy trigger is set per line appearance, counts the active calls on the line before CFB activates, and cannot exceed that line appearance's maximum number of calls.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Overview; Call Forward Busy · Checked 2026-10-02
23. 23
    Cisco recommends keeping the busy trigger slightly below the maximum number of calls so that users can still make outgoing calls and transfers.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Overview; Call Forward Busy · Checked 2026-10-02
24. 24
    Leaving a directory number's No Answer Ring Duration field empty makes Unified CM use the clusterwide Forward No Answer Timer service parameter.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Fields; No Answer Ring Duration (seconds) · Checked 2026-10-02
25. 25
    The No Answer Ring Duration value should be less than the T301 Timer service parameter.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Fields; No Answer Ring Duration (seconds) · Checked 2026-10-02
26. 26
    Call Forward No Answer applies when the phone is not answered before the No Answer Ring Duration timer expires, or when the destination is unregistered.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Overview; Call Forward No Answer · Checked 2026-10-02
27. 27
    Call Forward No Coverage applies when a hunt list is exhausted or the hunt timer expires and the hunt pilot is set to use the line group member's own forward settings (the option that replaced the Use Personal Preferences check box).

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Configure Call Forwarding when Hunt List is Exhausted or Hunt Timer Expires; Hunt Call Treatment Fields for Call Forwarding · Checked 2026-10-02
28. 28
    The Max Forward UnRegistered Hops to DN service parameter limits how often a call can be forwarded because of an unregistered DN, and Unified CM terminates the call when that limit is exceeded.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Configure Other Call Forwarding Types; Call Forward Unregistered · Checked 2026-10-02
29. 29
    Call Forward Unregistered reroutes calls for an unregistered directory number, for example during a WAN link failure, and can be set separately for internal and external callers.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Overview; Call Forward Unregistered · Checked 2026-10-02
30. 30
    Unity Connection's default Attempt Forward forwarded-routing rule sends calls forwarded from a user extension to that user's greeting.

    System Administration Guide for Cisco Unity Connection Release 15 - Call Management · Call Management; Call Routing; default forwarded routing rules · Checked 2026-10-02
31. 31
    Unity Connection's Check Telephony Configuration link (Telephony Integration > Port Group > Related Links) validates the integration and suggests fixes when the check fails.

    Configuration Example for CUCM Non-Secure SIP Integration with CUC · Verify · Checked 2026-10-02
32. 32
    When Unity Connection receives a call it first decides whether the call is direct or forwarded and then applies the matching call routing table.

    System Administration Guide for Cisco Unity Connection Release 15 - Call Management · Call Management; Call Routing (direct and forwarded routing rules) · Checked 2026-10-02
33. 33
    Unity Connection's default forwarded Opening Greeting rule sends calls forwarded from an extension not associated with a user account to the Opening Greeting.

    System Administration Guide for Cisco Unity Connection Release 15 - Call Management · Call Management; Call Routing; default forwarded routing rules · Checked 2026-10-02
34. 34
    Unity Connection routing rule conditions include calling number, dialed number, forwarding station, port or trunk, phone system and schedule, and a blank condition matches everything.

    System Administration Guide for Cisco Unity Connection Release 15 - Call Management · Call Management; Call Routing; rule conditions · Checked 2026-10-02
35. 35
    Unity Connection evaluates routing rules in order and routes the call by the first rule whose conditions all match.

    System Administration Guide for Cisco Unity Connection Release 15 - Call Management · Call Management; Call Routing · Checked 2026-10-02
36. 36
    Cisco's CUCM-to-Unity Connection SIP integration example has both Redirecting Diversion Header Delivery - Inbound and Redirecting Diversion Header Delivery - Outbound checked on the Unified CM SIP trunk.

    Configuration Example for CUCM Non-Secure SIP Integration with CUC · Configure; SIP trunk inbound calls and outbound calls settings · Checked 2026-10-02
37. 37
    In Unified CM the voice mail pilot (Advanced Features > Voice Mail > Voice Mail Pilot) is created first, and a voice mail profile that selects that pilot is created after it; either can be made the system default.

    Configuration Example for CUCM Non-Secure SIP Integration with CUC · Configure; Steps 13 and 15 · Checked 2026-10-02
38. 38
    The RFC 5806 diversion-counter parameter records the cumulative number of diversions, and the ISUP interworking maps the ISUP redirection counter to the top-most Diversion header's counter.

    RFC 5806: Diversion Indication in SIP · Section 4; Section 9.2.3 · Checked 2026-10-02
39. 39
    RFC 5806 is a Historic RFC; its IESG note says the Diversion proposal was not standardised and points to RFC 4244 (History-Info) as the standards-track mechanism for request history.

    RFC 5806: Diversion Indication in SIP · Status of This Memo; IESG Note · Checked 2026-10-02
40. 40
    Under RFC 5806, a request that has been diverted more than once carries Diversion entries with the most recent diversion top-most.

    RFC 5806: Diversion Indication in SIP · Section 4 (header syntax and ordering) · Checked 2026-10-02
41. 41
    RFC 5806 defines Diversion header reason values including unknown, user-busy, no-answer, unavailable, unconditional, time-of-day, do-not-disturb, deflection, follow-me, out-of-service and away.

    RFC 5806: Diversion Indication in SIP · Section 4 · Checked 2026-10-02
42. 42
    A Dialed Number Analyzer Phones analysis applies both the device CSS and the selected line's CSS to the test.

    Troubleshoot Call Routing Issue via CUCM Dialed Number Analyzer · Key Features and Use Cases of Dialed Number Analyzer; Phones · Checked 2026-10-02
43. 43
    Dialed Number Analyzer results show a result summary, the call flow with matched translation and route patterns and the destination trunk or gateway, and alternate matches.

    Troubleshoot Call Routing Issue via CUCM Dialed Number Analyzer · Key Features and Use Cases of Dialed Number Analyzer; results · Checked 2026-10-02
44. 44
    To use Dialed Number Analyzer, activate the Cisco Dialed Number Analyzer and Cisco Dialed Number Analyzer Server services in Cisco Unified Serviceability (Tools > Service Activation), then open https://<cucm>/dna.

    Troubleshoot Call Routing Issue via CUCM Dialed Number Analyzer · How to Enable and Access Dialed Number Analyzer · Checked 2026-10-02
45. 45
    One way to check whether a forward destination is reachable is a Dialed Number Analyzer Calling Search Space or Phones analysis that dials the forward destination and matches the CSS the forward will use; DNA by itself does not show the forwarding CSS.inferred

    Troubleshoot Call Routing Issue via CUCM Dialed Number Analyzer · Key Features and Use Cases of Dialed Number Analyzer · Checked 2026-10-02
46. 46
    If a forwarding Calling Search Space field is set to None in a system that uses partitions and calling search spaces, the forward operation fails.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Fields; Calling Search Space field descriptions · Checked 2026-10-02
47. 47
    When an administrator chooses a forwarding calling search space for internal calls, Unified CM automatically copies that value into the matching external-calls CSS setting.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Fields; internal calling search space note · Checked 2026-10-02
48. 48
    Forward Busy and Forward No Answer each have separate Internal and External Calling Search Space fields on the directory number.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Fields; Forward Busy Internal/External and Forward No Answer Internal/External · Checked 2026-10-02
49. 49
    The Forward Maximum Hop Count service parameter sets the maximum number of times one call can be forwarded or diverted.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forward All, Including CFA Loop Prevention and CFA Loop Breakout; Forward Maximum Hop Count · Checked 2026-10-02
50. 50
    For incoming QSIG calls Unified CM caps diversions at 15 regardless of a higher Forward Maximum Hop Count, and Cisco recommends setting the parameter to 15 when QSIG trunks are configured.

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Interactions; Forward Maximum Hop Count and QSIG · Checked 2026-10-02
51. 51
    A forward to an external PSTN number that is rejected at activation or fails at call time most likely means the relevant forwarding CSS (CFA primary plus secondary, or the busy or no-answer internal or external CSS) contains no partition holding a route pattern that matches the destination.inferred

    Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Call Forwarding · Call Forwarding Fields; Forward All Calling Search Space and Secondary Calling Search Space for Forward All · Checked 2026-10-02
52. 52
    For call-processing analysis, Cisco's trace collection technote has the Cisco CallManager service's Debug Trace Level set to Detailed (and Enable All Trace for the CTIManager service).

    Collect Trace Data from a CUCM Cluster · Configure or Confirm Detailed Tracing for the CallManager Service; Configure or Confirm Detailed Tracing for the CTI Manager Service · Checked 2026-10-02
53. 53
    The technote collects Cisco CallManager, Cisco CTIManager, Event Viewer-Application Log and Event Viewer-System Log from all cluster servers through RTMT Trace & Log Central with an absolute time range.

    Collect Trace Data from a CUCM Cluster · Gather the Requested Traces · Checked 2026-10-02
54. 54
    For each reproduced test call, Cisco asks for the calling number, the called number, and the call start and end times so the trace can be located.

    Collect Trace Data from a CUCM Cluster · Reproduce the Issue and Take Notes · Checked 2026-10-02
55. 55
    A forward busy or no answer call that reaches the Unity Connection Opening Greeting instead of the user's greeting most likely arrived either without redirecting information (handled as a direct call) or with a forwarding number that matches no user extension.inferred

    System Administration Guide for Cisco Unity Connection Release 15 - Call Management · Call Management; Call Routing; default direct and forwarded routing rules · Checked 2026-10-02

Documents

Cite this page

WarmTransfer. (2026, October 2). Troubleshooting call forwarding that fails in Unified CM. WarmTransfer. https://warmtransfer.net/knowledge/cucm-call-forward-troubleshooting

@misc{warmtransfer-cucm-call-forward-troubleshooting,
  title  = {Troubleshooting call forwarding that fails in Unified CM},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/cucm-call-forward-troubleshooting},
  note   = {Verified 2026-10-02}
}