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Cisco Bug: CSCte81646 - Layer3 Outage on Cable Modems when BPI+ TEK Sequence Number Wraps

Last Modified

Jan 28, 2017

Products (1)

  • Cisco uBR10000 Series Universal Broadband Routers

Known Affected Releases


Description (partial)


Periodically CMs loose l3 connectivity on 2020 linecards.  The interval is determined by the TEK life-time configured at the MAC Domain.  Using the default TEK life-time or 12 hours, the outage occurs after 3.5 days which allows for 14 key requests by the modem and lasts for 6 hours.  The modem recovers automatically after these 6 hours and the cycle repeats itself.  The calculations are as follows:

14 key exchanges * 1/2 TEK life-time = 3.5 days
1/2 TEK life-time outage = 6 hours

If the default is changed from 12 hours, the above calculations can be used to determine the interval in which this happens.


This outage occurs during normal operation and is caused by a problem decrypting the upstream traffic at the time the modem uses key sequence 15 to encrypt the traffic.  At the time of the outage, the sequence number will be configured as follows on the CMTS:

dhegglin-10k#scm 001c.107f.a916 privacy verbose | i Sequence Number
Latest Sequence Number  : 0
Current Sequence Number : 15
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