Why do we need to create VLANs to break a broadcast domain when the router can do the same?

1.Breaking broadcast domain through VLAN- enter image description here

  1. Breaking broadcast domain through Router- enter image description here

1 Answer 1


VLANs will let a single switch act as if it was a several switches. A router is required to allow traffic to get from one VLAN to another VLAN.

Routers typically have few physical interfaces (router interfaces are expensive compared to switch interfaces), so it may be impractical to use router physical interfaces to break your network into multiple physical LANs. Most business-grade routers will let you create multiple virtual interfaces on a single physical interface. Each virtual interface will be a separate VLAN, and you use 802.1Q tagging to separate the traffic for each VLAN.

Example of a router on a stick (using your own diagrams):

enter image description here

  • So If we want to communicate with other VLANs, we should use routers, and if we dont want, we should use a single switch. Am I correct here? Feb 25, 2018 at 20:41
  • It depends on what you are trying to accomplish. If you do not need hosts on one LAN to communicate with hosts on a different LAN, then you could have multiple separate switches, or you could have a switch with multiple VLANs (makes the switch act as separate switches). Often, you will have a switch with VLANs that connects to a router via a trunk link so that the router can route the traffic between VLANs (router-on-a-stick), and you may use ACLs to restrict traffic between the VLANs.
    – Ron Maupin
    Feb 25, 2018 at 20:44
  • To route between VLAN's you don't router, you can use Layer 3 switch. Feb 25, 2018 at 20:50
  • 4
    A layer-3 switch is a layer-2 switch with a router module, so you are using a router. Conceptually, it is a router-on-a-stick connected to a layer-2 switch. Remember that a layer-3 switch is first a layer-2 switch, but it has an internal router, too.
    – Ron Maupin
    Feb 25, 2018 at 20:53

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