Network PC World

  MST (Multiple Spanning Tree) – 802.1s Overview: Purpose : MST reduces the number of STP instances by mapping multiple VLANs to a single STP instance, improving efficiency and minimizing CPU cycles. Compatibility : MST is backward-compatible with 802.1D (CST), 802.1w (RSTP), and Cisco’s proprietary PVST+. MST Region : A group of interconnected switches with the same MST configuration. Switches in the same region appear as a single virtual switch to external devices. MST Features: MSTI (MST Instance) : Maps one or more VLANs to a single STP instance, reducing the number of required STP instances. Load Balancing : VLANs are distributed across multiple MST instances, allowing better load distribution across the network. IST (Internal Spanning Tree) : The default instance (MSTI 0) runs on all switch ports and is responsible for managing VLANs not assigned to other instances. MST Configuration Key P

Spanning Tree Protocol (STP) Overview: STP (802.1D) : Builds a loop-free Layer 2 topology by blocking redundant paths. STP Types : 802.1D : Legacy STP. 802.1w : Rapid Spanning Tree Protocol (RSTP). 802.1s : Multiple Spanning Tree Protocol (MSTP). Root Bridge : The central switch in the STP topology; all ports are forwarding. BPDU (Bridge Protocol Data Units) : Used to exchange STP information. Configuration BPDU : Identifies root, root ports, designated ports, and blocking ports. Topology Change Notification (TCN) BPDU : Notifies other switches of topology changes. Key STP Terms: Root Path Cost : The cumulative cost from a switch to the root bridge. System Priority : Used in root bridge selection, default is 32,768. Max Age : Time BPDU information remains valid (default 20 seconds). Hello Time : Interval for BPDU advertisement (default 2 seconds).

  EtherChannel Overview: EtherChannel groups multiple trunk, access, tunnel, or routed ports into one logical port. Configuration settings are placed in the port-channel interface. Layer 2 vs. Layer 3 : Member interfaces need to be in the correct layer before being associated with a port-channel. Useful Commands: show lacp neighbor show etherchannel summary show lacp sys-id clear lacp counters to reset LACP counters. PAgP (Port Aggregation Protocol): PAgP silent mode : Operates even with non-PAgP devices. Non-silent mode : Faster connection with PAgP-compliant switches. MLAG (Multi-Chassis Link Aggregation Protocol): Synchronization happens between switches over the control plane . On VSS (Virtual Switching System) , control plane is synchronized over Virtual Switch Link (VSL) , typically 2x10G LAG. vPC (Virtual PortChannel): Available on Nexus Series switches.