Switching verses Routing OSI stack 7-layer OSI stack

BL Study Plan  2110 Topo 

What you will learn on this page


This lesson explains Switching verses Routing and how it fits into the SMPTE ST 2110 stack.

• Differences


Differences


Bottom Line  

  1. What they do
    1. Switching (Layer-2): Forwards frames inside a single Layer-2 network (VLAN) using MAC addresses. Builds a MAC/CAM table by learning source MACs on ports. Uses STP/RSTP/MSTP to prevent loops. Can constrain multicast with IGMP Snooping.
    2. Routing (Layer-3): Forwards packets between IP subnets using IP addresses. Chooses next-hops via routing tables learned statically or by OSPF/IS-IS/BGP. Handles TTL, fragmentation, and policies like NAT, ACLs, PBR.
    Bottom Line  
  2. Control planes & protocols
    1. Switching: STP family, LLDP/CDP, 802.1Q VLANs, LACP, IGMP Snooping.
    2. Routing: OSPF/IS-IS (IGPs), BGP (EGP), static routes, PIM (multicast routing).
    Bottom Line  
  3. Data plane decisions
    1. Switch: Lookup dest MAC → egress port (per-VLAN). Unknown unicasts flood within the VLAN. Broadcasts (ARP/DHCP) stay inside the VLAN.
    2. Router: Lookup dest IP → next hop/egress interface (RIB/FIB). No L2 flooding across subnets; broadcasts don’t cross the router.
  4. Boundaries they create
    1. Switch: Splits collision domains per port; a VLAN is one broadcast domain.
    2. Router: Splits broadcast domains; each IP subnet/interface is its own broadcast domain.
  5. Performance & latency
    1. Switching: Generally lowest latency, wirespeed L2 forwarding; huge port density.Routing: Slightly more overhead (L3 lookup, TTL, ACL/QoS/NAT), still wirespeed on modern silicon.
    Bottom Line  
  6. Multicast
    1. Switch: IGMP Snooping prunes delivery to only interested ports within a VLAN.
    2. Router: PIM (SM/SSM) and IGMP at L3 to carry multicast between subnets and across the WAN.
  7. Security & policy
    1. Switch: Port security (sticky MAC, limits), 802.1X, VLAN segmentation, Private VLANs, DHCP Snooping/ARP Inspection.
    2. Router: Inter-VLAN firewalling/ACLs, NAT, VPNs, segmentation between sites/tenants.
    Bottom Line  
  8. Where you use them (typical enterprise design)
    1. Access layer: Switching (user/device ports, PoE, VLANs, PortFast/BPDU-Guard).
    2. Distribution/Core: Routing between VLANs and sites; ECMP; OSPF/IS-IS; BGP to DC/ISP.
    3. Collapsed core / L3 switch: Many “switches” today are L3 switches—they do both: high-speed L2 and wire-rate L3 (SVIs, OSPF, BGP). The “router vs. switch” line is often about feature licenses/roles, not silicon.
  9. When to choose what
    1. Stay in L2 (switching) when:
      1. Devices must be in the same subnet/VLAN (e.g., IP cameras to a local recorder).
      2. You need simple, fast east-west connectivity inside a rack/floor.
    2. Route (L3) when:
      1. You need segmentation between networks (e.g., users vs. servers vs. control).
      2. You’re crossing sites, doing policy/QoS, NAT, or multicast across subnets.
      3. You want fault isolation—broadcast storms or loops in one VLAN won’t impact others.
    Bottom Line  
  10. ST 2110 / media-centric notes
    1. Inside a 2110 production VLAN, use switching with proper IGMP Snooping (+ querier if no L3) to keep multicast flows scoped.
    2. Between production islands / to cloud / to MCR, use routing (often OSPF/IS-IS internally, PIM for multicast, and BGP toward WAN/cloud).
    3. Determinism: prefer P2P routed links for backbone paths; keep VLAN blast radius small; size buffers/QoS for PTP, audio, and video flows.

    Sumary:
    Switching = L2, MAC-based, inside a VLAN.
    Routing = L3, IP-based, between subnets.

    Modern L3 switches do both, so the “versus” is mostly about where in the topology you apply L2 vs. L3 functions.

     



     

    UPDATED
    5/20/26
    V260520-1.0