STP - determining the blocked port using port ID


In the event that you connect one switchport to another switchport on the **same** switch, [STP](/spanning-tree-protocol-stp) will still choose a port to put into the blocked [port role](/stp-port-roles) based on the [Port ID](/stp-port-identification).  This is a special case of the [determination f the blocked port using the Port ID](/stp-determining-the-blocked-port-using-port-id).  

In such a case, regardless of whether or not the switch is the [root bridge](/stp-root-bridge-selection), all of the same criteria will be checked. Because both ports are on the same switch, both ports are considered receiving and sending ports. So ultimately, it is the port with the highest port ID that will be blocked.


Links:

https://forum.networklessons.com/t/spanning-tree-reconvergence/1346/33?u=lagapidis

https://networklessons.com/cisco/ccie-routing-switching-written/spanning-tree-cost-calculation

https://networklessons.com/cisco/ccie-routing-switching-written/spanning-tree-reconvergence

STP - connecting one port to another port on the same switch

SPAN using VLANs as a source on a Nexus device

SPAN

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STP - BPDUGuard, BPDUFilter, and Portfast

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STP - BPDUs, VLAN IDs, and PVST+

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STP - Factors to Consider When Choosing a Root Bridge

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STP - Understanding MST regional root identifier and proposal-agreement process

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STP - UplinkFast

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STP configuring on EtherChannel

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STP contents of a BPDU

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STP determining blocked port using cost

STP direct vs indirect link failure

STP fine tuning the spanning tree protocol

STP how a switch identifies a BPDU

STP how to find the root bridge

STP interface type

STP prio nbr value

STP topology change process

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STP - connecting one port to another port on the same switch

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