Core: Layer 2 Control Plane
In one line A Layer 2 domain is a single broadcast and failure domain that floods to learn - so the master rule is keep it small and push routing toward the edge. How L2 behaves Switches flood-and-learn: unknown unicast/broadcast/multicast floods to every port in the VLAN,
Core: Layer 2 Control Plane
In one line Convergence starts at the wire: how fast a device detects a failure sets the floor for everything STP, aggregation, or routing can do above it. Down detection * Physical loss of signal / light - fastest; the interface goes down immediately. * Protocol keepalives - needed when the physical layer stays up
Core: Layer 2 Control Plane
Requirement / business driver Provide a loop-free active L2 topology with automatic recovery, while bounding the blast radius of L2 faults. The variants VariantNotes STP (802.1D)Original; slow (30-50 s). Legacy only. PVST+ / Rapid-PVST+Per-VLAN trees; RPVST+ is fast (RSTP per VLAN) - common Cisco default. RSTP
Core: Layer 2 Control Plane
Requirement / business driver Use all redundant links (not STP-blocked ones) and remove single points of failure, without creating loops. Options * LACP / EtherChannel - bundle parallel links between two devices into one logical link. * MLAG / vPC - two switches present a single LAG to a dual-homed device; both forward (dual-active)
Core: Layer 2 Control Plane
In one line Without snooping a switch floods multicast like broadcast to every port - snooping constrains it to only the ports that asked. The pieces * IGMP (IPv4: v2 ASM, v3 SSM) and MLD (IPv6: v1 ~ IGMPv2, v2 ~ IGMPv3) are how hosts signal group membership. * IGMP / MLD snooping lets the switch
Core: Layer 2 Control Plane
Requirement / business driver Bound the blast radius of L2 faults and make the access/distribution layer resilient - without the "redundancy" secretly being a single failure. The four levers (blueprint 2.5) * Fate sharing - the subtle one. Two uplinks down the same conduit, or a shared control plane (VSS/