Hi All,
I wanted to share an issue I faced recently with HSRP between two Cisco Catalyst 3850 switches in a distribution layer setup.
The Problem:
We noticed that the HSRP active/standby roles kept flapping every few minutes, causing intermittent packet loss for end users. Logs showed frequent changes in HSRP state and %HSRP-5-STATECHANGE messages.
Troubleshooting Steps:
- Checked interface configs and VLAN assignments → all correct.
- Verified trunking and allowed VLANs → no issues.
- Examined HSRP configuration → priority with preemption was configured, but timers were left at default.
- Inspected CPU load → spikes during reconvergence when many devices were active.
The Root Cause:
After a deeper look, it turned out that HSRP timers (hello/hold) combined with some minor interface errors were contributing to the instability. When the default timers (hello 3 sec / hold 10 sec) were used in a high‑traffic environment, even small delays were enough to cause state changes.
Solution:
- Tuned HSRP timers → set standby timers 1 4 for faster hello/hold intervals.
- Fixed physical interface errors by replacing a faulty fiber patch cable.
- Increased HSRP priority on the intended active switch to keep roles consistent.
Result:
HSRP stabilized, no more flapping, and user packet drops stopped completely.
I’m sharing this here in case others face similar issues. Has anyone else experienced HSRP instability due to timers and interface errors? Would love to hear how you normally tune HSRP for high‑availability designs.
Thanks,
Md. Irshad Ansari
