From: gladston@br.ibm.com
Date: Mon Apr 11 2005 - 17:19:27 GMT-3
I found this statement on 4500 doc, but not on 3550 doc (I think it must be the same)
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By default, spanning tree sends BPDUs from all ports regardless of whether PortFast is enabled
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Yet, I could not clarify this behavior:
If the switch is configured with Portfast and the port receives a BPDU, what does happen?
Based on the following doc, if the switch is configured with Portfast plus BPDU filtering, when the port receives a BPDU it loses its portfast status and bpdu filtering is disabled.
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Understanding BPDU Filtering
The BPDU filtering feature can be globally enabled on the switch or can be enabled per interface, but the feature operates with some differences.
At the global level, you can enable BPDU filtering on Port Fast-enabled ports by using the spanning-tree portfast bpdufilter default global configuration command. This command prevents ports that are in a Port Fast-operational state from sending or receiving BPDUs. The ports still send a few BPDUs at link-up before the switch begins to filter outbound BPDUs. You should globally enable BPDU filtering on a switch so that hosts connected to these ports do not receive BPDUs. If a BPDU is received on a Port Fast-enabled port, the port loses its Port Fast-operational status, and BPDU filtering is disabled.
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Thanks for any feedback. I previously posted this doubt but reading some docs I saw this topic is not clear yet.
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