Differences

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--- networking:stp [2025/12/03 15:31] – [Port States] v1ctor
+++ networking:stp [2025/12/03 16:11] (current) – [Root Guard] v1ctor
@@ Line 27: / Line 27: @@
     - Root Port
     - Designated Port
+==== During Failure ====
+Root port sends BPDUs every 2 seconds. If non-root switch stops receiving BPDUs over Root port for 20 seconds, it starts the //Listening// and //Learning// process on the //Blocked// port. Failover time is 50 seconds.
+==== RSTP ====
+RST improves convergence time. Instead of having a //Blocked// port and spending too much time in //Listening// and //Learning//, we have **Alternate** port. Basically it's a second best port if Root port fails. When Root port fails, switch waits **max time out** (20 seconds) and starts forwarding traffic over the new Root port
+==== PORT-FAST ====
+When port flaps, switch sends TCN (topology change notification) message, which forces all switches to re-calculate the root switch. This is not very efficient when port towards the client flaps. In order to mitigate that, customer facing port is configured with **spanning-tree portfast**. This port will be always on (forwarding).
+==== BPDU Guard ====
+We should not receive BPDUs on the customer facing ports. There is a feature which sets the port to **err-disabled** state if switch receives a BPDU on that port.
+==== Root Guard ====
+Configuration on the Root switch to protect hijacking the Root role. Configured on the ports.
+==== MSTP ====
+Instead of sending BPDU for each VLAN, MSTP aggregates VLANs into the instances and send a single BPDU for that group.
+On Arista, by default MST instance 0 is created and all VLANs belong to that instance.