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What is the purpose of the relay?

What is the purpose of the relay?

  • On behalf of Chris Stelmar:

    In the baggy pants model you are referencing, the Relay sends a packet from one port to the other. This is useful in the situation where the destination MAC is different from the MAC of the device.

    The only piece of information a layer two switch needs to determine how it is forwarded or if it is forwarded is this.

    1. Is it for the CPU connected to me or not.
    2. Is it Multicast or not.

    Essentially once this information is known, the device will either consume the packet, forward it out the other port or do both.
    1. Multicast MAC and the device subscribes to said Multicast MAC – Send to the CPU and out the other port.
    2. Multicast MAC and the device does not subscribe to said Multicast MAC – Send out the other port.
    3. Unicast MAC that is the device CPU’s – Send to the CPU only.
    4. Unicast MAC that is not the device’s CPU – Send it out the other port.

    The relay essentially makes these decisions.