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Cisco Bug: CSCut08955 - NCS6k Leapsecond 2015

Last Modified

Apr 23, 2018

Products (3)

  • Cisco Network Convergence System 6000 Series Routers
  • Cisco NCS 6008 - 8-Slot Chassis
  • Cisco IOS XR Software

Known Affected Releases


Description (partial)

The Linux kernel on the NCS6000 may be affected by a "livelock" condition which can result in a hang or crash of the affected device.

To ensure the correct alignment of astronomical and atomic time, the International Earth Rotation & Reference Systems Service has called for an extra second (leap second) to be added to Coordinated Universal Time (UTC) at 23:59:59 on 30 June 2015. 

The leap second update will be propagated via Network Time Protocol (NTP) to devices where NTP is configured. The Network Time Protocol (NTP) subsystem is using a timer for triggering the leapsecond adjustment in the Linux kernel. When the leap second adjustment is done in the kernel, this may trigger the "livelock" condition described in the "Symptom" section.

This problem may happen to NCS6000 routers running 5.0.1 or 5.2.1 without the SMU (patch) for CSCut08955. NCS6000 routers running 5.2.3 and above are not affected.

For the NCS6000 routers running 5.0.1 or 5.2.1, the SMUs for CSCut08955 can be downloaded from in the Support section. Please note that 2 SMUs should be installed per router: one in the XR VM and one in the sysadmin VM.

For the NCS6000 routers running 5.0.1 or 5.2.1 where the SMUs can't be installed in time before June 30th 2015, the workaround described below should be applied to avoid this problem.

Related Community Discussions

Bug FYI - Leap Second Adjustment June 30, 2015 - affects 2.2(1b)A, 2.2(2c)A, 2.2(3a)A
"UCS-FI: reload or switchover may occur due to Leap second update" UCS:   Affected versions: 2.2(1b)A 2.2(2c)A 2.2(3a)A
Latest activity: Jun 26, 2015
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