Ishmam Ahmed — Blog

DTP explained here: DTP, stands for Dynamic Trunking Protocol, is a cisco proprietary protocol. DTP allows ports to be configured for operating trunk mode automatically based on which administrative mode the switchport is on and which administrative or manual mode the switchport that is connected to it is on. Interfaces on old switches, switchport mode is dynamic desirable but interfaces on new cisco switches, switch mode is dynamic auto. Trunk mode do not do DTP negotiation. Dynamic Desirable can form trunk, also actively want to form trunk. Dynamic Auto can form trunk but do not actively want to form trunk. Access port do not do DTP negotiation. DTP Administrative Mode Outcomes If a port is set to Trunk : With Trunk → Trunk With Dynamic Desirable → Trunk With Access → No trunk (X) With Dynamic Auto → Trunk If a port is set to Dynamic Desirable : With Trunk → Trunk With Dynamic Desirable → Trunk With Access → Access With ...

Rapid Spanning Tree Protocol starts here. This is how it works: Blocks ports to prevent loops. Same rules for root bridge selection as STP Same rules for root port selection as STP Same rules for designated port selection as STP Takes less than 30 seconds to move a port from blocking to forwarding state; thus, the name “Rapid”. 1st difference of RSTP from STP is RSTP root cost: STP vs RSTP Path Cost by Link Speed 10 Mbps STP cost: 100 RSTP cost: 2,000,000 100 Mbps STP cost: 19 RSTP cost: 200,000 1 Gbps STP cost: 4 RSTP cost: 20,000 10 Gbps STP cost: 2 RSTP cost: 2,000 100 Gbps STP cost: Not defined RSTP cost: 200 1 Tbps STP cost: Not defined RSTP cost: 20 2nd difference will be in port states: STP Port States (Discarding / Learning / Forwarding) Discarding (Stable) BPDUs: Send No / Receive Yes MAC learning: No Forward traffic: No Learning (Transitional) BPDUs: Send Yes / Receive Yes MAC learning: Yes Forward traffic: No Forwarding (Stable) BPDUs: S...

Continuing after Part 1 :   Blocking and Forwarding states are stable states. There are two other states: Listening & Learning. These are transitional state. I have tried to learn the different states in STP by differentiating them by a few things that they do or do not. These things are: 1. Do they send or receive STP BPDUs? 2. Do they learn mac addresses? 3. Do they receive and forward regular traffic? STP Port States (Summary) Blocking (Stable) BPDU: Send No / Receive Yes MAC learning: No Forward traffic: No Listening (Transitional) BPDU: Send Yes / Receive Yes MAC learning: No Forward traffic: No Learning (Transitional) BPDU: Send Yes / Receive Yes MAC learning: Yes Forward traffic: No Forwarding (Stable) BPDU: Send Yes / Receive Yes MAC learning: Yes Forward traffic: Yes  Wireshark STP packet capture:   Portfast : Portfast is called a toolkit (optional feature) of STP that solves one problem of STP. As soon as a s...

Spanning Tree Protocol (STP) is a Layer 2 protocol that prevents switching loops and broadcast storms by placing redundant links into a blocking state when necessary. Here what the protocol STP is and can do and is used for: STP is a layer 2 protocol. Stops layer 2 loops/broadcast storms. Used for redundancy. With STP it is possible to implement multiple paths to a destination. Done by changing the state of a redundant port to blocking state. Blocking state ports can change to forwarding state if any forwarding port fails. By putting some ports in forwarding and some ports in blocking, there is always a single path between two points in a network. How it works: Ports that have STP enabled sends and receives “Hello BPDU” messages. Hello BPDU messages are send out of STP enabled ports every 2 seconds. BPDU stands for Bridged Protocol Data Unit. If Hello BPDU message is received on any STP enabled port, the switch that receives it understands that the interface that the STP enabled port ...