Cisco CCNP BCMSN Exam Tutorial BPDU Skew Detection
Below is a MRR and PLR article in category Computers Technology -> subcategory Computer Certification.
Cisco CCNP BCMSN Exam Guide: BPDU Skew Detection
Overview
Discover how BPDU Skew Detection helps prevent unnecessary STP recalculations from Chris Bryant, CCIE
12933.
Key Concepts
- BPDU: Bridge Protocol Data Unit
- STP: Spanning Tree Protocol
- Skew Detection: Identifying delayed BPDU relays
Introduction
Wondering about BPDU Skew and its importance? Essentially, we're looking to identify BPDUs that aren't relayed promptly.
How BPDU Skew Detection Works
After the root bridge is elected, it sends BPDUs, which non-root switches relay through the STP tree. Ideally, BPDUs are sent and relayed every two seconds, known as the "hello time." However, real-world networks often face delays.
Common Issues
- Busy switches struggling with CPU load may delay relaying BPDUs.
- BPDUs might be lost during transmission.
Importance of Skew Detection
To prevent unnecessary STP recalculations, Skew Detection acts as a notification tool. While it doesn't stop the recalculations, it alerts network administrators via syslog messages when delays occur.
Handling Notifications
A heavily loaded CPU could be overwhelmed by constant skew messages. To manage this, notifications are limited to one per minute unless the delay, known as "skew time" or "BPDU latency," is critical.
Critical Skew Time
A skew time is considered critical if it exceeds half of the MaxAge value, specifically when it hits 10 seconds or more. When this happens, syslog alerts are sent immediately without delay.
By understanding and implementing BPDU Skew Detection, you can maintain optimal network performance and avoid unnecessary recalibrations in the STP topology.
You can find the original non-AI version of this article here: Cisco CCNP BCMSN Exam Tutorial BPDU Skew Detection.
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