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Cisco Bug: CSCvt36385 - cBR8 CPU Process 'DHCPv6 Relay' high after IOS-XE Upgrade and Large sv-match-unknown Lease Queries

Last Modified

Sep 10, 2020

Products (2)

  • Cisco cBR Series Converged Broadband Routers
  • Cisco cBR-8 Converged Broadband Router

Known Affected Releases

16.12.1

Description (partial)

Symptom:
After upgrading to 16.12.1y, we observed high process "DHCPv6 Relay" in the range of ~18% 5-minute average. We observed COPP Policy rate-limit dropping DHCPv6 Solicit packets. After increasing the COPP to 1000 pps from 100 pps the CPU increased to ~25% 5-minute average (in a way this makes sense as no more DHCPv6 Solicits were rate-limited).

We then (unrelated) reset the standby SUP and the same DHCPv6 relay process dropped to a fraction of the value (1.5% 5-minute average). This DDTS is to track the stby SUP reset.

Conditions:
High amounts of Punt-type "sv-match-unknown" because of v6 CPE or hosts. cBR8 with lots of load (56k CMs, and equal or larger number of CPEs). Also cBR8 is sending lease queries to the DHCPv6 server, but not getting a response.
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