Difference between Subnet and VLAN?

  • You often hear the terms Subnet and VLAN used interchangeably. With the ubiquitous nature of IP these days, when are the two not considered roughly the same from a high-level, understanding that VLANs are L2 and Subnets are L3. In other words, are there any cases for having a VLAN without a Subnet, and still have IP (L3) communication? [Also ignoring that all networks are not subnets when considering classful networks which all are really just CIDR prefixes these days.]

  • ytti

    ytti Correct answer

    8 years ago

    If they are used interchangeably then they are used incorrectly.

    Subnet refers to particular IP network, such as 192.0.2.0/28.

    VLAN refers to 802.1Q standard, in which you can essentially give each port unique MAC address table, effectively separating them from each other.

    VLAN may transport one or more subnet (but does not have to, it may be transporting something else than IP entirely). Subnet may be configured for VLAN, but does not have to be, it could be without 802.1Q or over some completely different L2 technology than ethernet.

    The last paragraph is closer to what I was looking to see, though the question was phrased around IP only.

    But to use them interchangeably you would need to remove all other conditions. Maybe in some companies VLANn has direct, unambiguous mapping to subnet Y, but it does not mean you could use them interchangeably in any practical way.

    VLANs are a way to split a single L2 media into multiple Broadcast Domain, effectively creating "virtual" layer 2 networks VLANs are usually used in switches to separate ports into distinct network The actual separation depends on the architecture, it can be along administrative lines (departments) or technological lines (PC, Server, IP Phones, Printers) The 802.1Q Standard is only for Trunking purpose (multiple VLAN in a single link), by way of a Tag that is included in the 802.1Q Header that is inserted in the Ethernet Header and is a must when connection multiple switches using VLANs

    Devices are not VLAN aware.

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Content dated before 7/24/2021 11:53 AM