Cisco IOS LAN Switching Command Reference - Spanning-Tree Commands: spanning-tree
[vlan vlan-list] forward-time seconds
"Use the spanning-tree forward-time command in global configuration mode or the
spanning-tree vlan forward-time command in interface configuration mode to set the time
that a Layer 2 port waits before it changes from the listening and learning states to the
forwarding state."
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Source: Cisco. (Specific document version varies, e.g., Catalyst 9300 Series Switches, IOS
XE Bengaluru 17.6.x). A general reference can be found in Cisco IOS command references
for switches. Example: Cisco Catalyst 3750 Switch Software Configuration Guide,
12.2(25)SEE - "Configuring STP" section, "STP Timers".
CCNA 200-301 Official Cert Guide, Volume 1 by Wendell Odom (Cisco Press):
Chapter 3: "Spanning Tree Protocol Concepts" discusses STP timers. "Forward Delay: The
number of seconds an interface stays in the listening state, and then the number of seconds
an interface stays in the learning state. Default: 15 seconds."
Source: Odom, W. (2019). CCNA 200-301 Official Cert Guide, Volume 1. Cisco Press.
(Chapter on STP).
Cisco documentation on "Understanding and Configuring Spanning Tree Protocol (STP) on
Catalyst Switches":
This document typically explains the STP timers: "Forward DelayThe time that is spent in
the listening and learning state. The default is 15 seconds."
Source: Cisco Systems, "Understanding and Configuring Spanning Tree Protocol (STP) on
Catalyst Switches" (available on Cisco.com, specific document ID may vary by switch
model and IOS version).