STP Question

dontstop · February 2017

Based on the excerpt attached, Am I correct in saying that this is alluding to all devices in an STP topology will perform a listening process for 15 seconds and timeout their MAC table entries across the entire topology?

I'm struggling to get PT to simulate this scenario. MAC table entries are not timing out as expected.

Edit: Just found a document reading it now: http://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/12013-17.html

dontstop · February 2017

Switches forward Ethernet frames based on their MAC address tables (filtering tables) that bind MAC addresses to egress ports. When a change in topology occurs (e.g. a link failure) the MAC address tables may appear to be invalid, as the paths between switches have changed. The switches may eventually re-learn the new information, but it may take considerable time, especially if the traffic is scarce and MAC address aging time is large (5 minutes by default). Based on that, if switch detects a change in the topology (e.g. link going up or down), it should notify all other switches that something has changed. In response to this notification, all switches will reduce their MAC address aging time to Forward_Time (15 secs by default) effectively fastening the aging process.

Understanding STP Convergence, Part I

I think it might not be wise to use PT for STP analysis

Danielh22185 · February 2017

PT is nothing but a simulator. I would tread carefully when trying to do hardware related functions / testing in it. You can obtain some switches on ebay for a very cheap price. I would suggest starting there or even looking into trying to emulate it with GNS3 using IOU, however even GNS3 / IOU isn't perfect.

wseyller · February 2017

Actually STP is what finally moved me from packet tracer to real equipment. It just doesn't work fully 100% in PT and some command are missing, so you don't get the full experience.

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