STP keeps blocking my ports — how do I troubleshoot?
ben31833 · posted · 62 views
I have a network with redundant links between switches and STP is blocking ports I need. I understand STP prevents loops but how do I control which ports get blocked? How do I check which switch is the root bridge? And should I use portfast on access ports?
- STP is doing its job — it blocks redundant paths to prevent broadcast storms. Check which switch is root with show spanning-tree. The switch with the lowest bridge priority (or lowest MAC if tied) wins. If the wrong switch is root, lower its priority with spanning-tree vlan 1 priority 4096. — Yaron,
- For access ports connecting to PCs, definitely use spanning-tree portfast. It skips the 30-second listening/learning delay so PCs get connectivity instantly. But NEVER put portfast on a port connected to another switch — it can cause temporary loops. Also add bpdu guard as a safety net. — itayitayy,
- I checked and SW2 was root because it had a lower MAC. Changed the priority on SW1 with spanning-tree vlan 1 priority 4096 and now the right switch is root and the ports I need are forwarding. Exactly what I needed, thanks. — ben31833,
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