Credit to @SpanningTreeDC on Twitter for the awesome STP logo! Wanted to throw some notes on here on which STP features are global, interface level, how the global configs will impact interfaces that are configured and also how error-recovery can save the day when you don't want to have to shut/no shut every err-disable interface … Continue reading Pretty easy read on STP Sub-Commands, what they do, errdisable demo, some labbing, lots of good info for exam day!
I started freestyle labbing to review some topics, and found some interesting behaviors along the way I wanted to make note of here, so this will be more of a troubleshooting / behaviors demonstration than a configuration of any particular topic. The topic I went with here is creating VLANs local to their respective switches, … Continue reading SWITCH Lab – Manual VLAN Pruning on Trunk interfaces, STP / EtherChannel behaviors, SWITCH and TSHOOT lab!
The following will be used for labbing RSTP, with a lot going on there, so lets hit it! Fundamentals of 802.1w RSTP, similarities and difference from 802.1d STP RSTP is Rapid Spanning-Tree Protocol IEEE 802.1w, the evolution of 802.1 PVST STP that we have been labbing (default STP is PVST), RSTP is also … Continue reading RSTP – Fundamentals, Port States and Link Types explained IN DEPTH, configured and verified on the lab!
The above Topology represents a failure on a Fiber Optic Transmit / Receive cable pair on one cable, on one end of the link, which would leave the link up and Unidirectional. Here is an example of the SFP Transceiver and Fiber cable connecting to a switch: Source : This Cisco.com 2960x Fiber Stacking article … Continue reading STP – Fiber Cabling, Loop Guard and UDLD DEEP DIVE, and important notes for exam day!
In this Topology everything is default, so SW1 has one the Root Bridge election with the lowest MAC Address as the tie breaker, and all port states were dynamically calculated. There is a lot to hit on these multiple STP topics, so, without further ado! First a quick peek at a great verification command … Continue reading STP – Root Guard, BPDU Guard, and BPDU Filter mechanics, behaviors, and verification labbed!
Note that SW4 is the 3560 that survived the purge of old switches in my lab, and its interfaces do show as Fa0/X instead of Fa1/0/X, so be aware of that with output. Spanning-Tree Portfast STP Portfast configuration allows an STP Port to go straight from Blocking Mode to Forwarding mode, skipping the … Continue reading STP – Portfast, Direct vs Indirect Link failure illustrated, Uplinkfast, and Backbonefast labbed!
For this lab I will be using the STP Topology with the default link states shown above, however I have reduced the additional VLANs to 10 / 20 / 30, to generate less output when comparing STP behaviors from changing the Root Bridge on specific VLANs. SW1 will be made the Root Bridge for VLAN … Continue reading STP – Configuring and verifying Root Bridge, behaviors from configs, Priority configruation + sys-id-ext labbed!
Consider the above Topology running STP with default settings, with 6 additional VLANs to the default Native VLAN 1, which links will be in what status by default? Equal Cost link speeds in a default STP Port Selection process First lets review the Root Port default election criteria once more: Port that receives … Continue reading STP – Root / Designated / Blocking Port selection process, illustrated for both equal and unequal STP Cost diagrams!
Boring repeat of the same old Topology, but works perfectly for review, so lets do it! To review the STP timers the command "show span vlan #" is used depending on which VLAN you are looking for, in this case it is VLAN 30 throughout this lab: SW2#sh span vlan 30 VLAN0030 Spanning tree enabled … Continue reading STP Timers – Aging Time value, defaults covered, important exam day root vs non-root behaviors labbed!
Above is a design issue that may be present on exam day or on the job, the issue being that as indicated in the top right corner there are 4 VLANs configured on both sides of the Trunks, but SW2 has interface Fa1/0/2 set to blocking - So only one link is being used for … Continue reading STP – Interface Cost config, VLAN load balancing with PVST and Port Priority, and verification commands labbed!
Most of this demonstration will be on the above Topology, except for the the output for changing Port cost, for that I'll just be using 2 Trunk links between SW1 and SW2. STP Link Speed to Path Cost, and how to change Path cost on an interface The link speed to STP cost … Continue reading STP – Path cost info, identifying the Root Bridge, Root Cost vs Path Cost, and debugging STP port state transitions!
This is an example of STP doing what it does best, and that is putting the Amber lit port 2 in "Blocking" state, to prevent a Switching Loop from forming. This is the logical Topology for a better idea of what's plugged into what: This post is focused on the "original" STP, all the fundamentals … Continue reading STP – Spanning-Tree Protocol Fundamentals, Root Bridge Election, BIDs and BPDUs, STP Port Roles / States!