Why does it take so long to pass traffic after rebooting?

Products

• PacketShaper

Issue/Introduction

Rebooting PacketShaper takes more than 50 seconds to pass traffic, even though the relays have closed correctly.

This is a common problem in a switch environment and can be avoided by making sure the Cisco switch has PortFast enabled on the port to which PacketShaper is connected.

 

Resolution

What is PortFast? PortFast allows Spanning-Tree to perform its four basic steps in reverse.

The normal Spanning-Tree sequence is:

Blocking (20 sec.) - Listening (15 sec.) - Learning (15 sec.) - Forwarding

With PortFast enabled, the sequence is:

Forwarding – Learning – Listening – Blocking

This allows traffic to first pass through on the switch port, instead of being blocked. Make sure all NICs connected are hard set to the same speed. This will also help in a shorter downtime since you do not have to worry about the unpredictable nature of auto-negotiation.