Traffic Prioritization in the LAN: Layer 2 or Layer 3?

• Prioritization at Layer 3, IPToS or RSVP, requires Layer 3 devices end-to-end

• LANs consist largely of Layer 2 switches

  • Majority of the edge connections are Layer 2 switches
  • Campus backbones will be GbE or ATM switches (non-Layer 3)
  • Layer 3 switches/routers understand Layer 2 (IEEE-802.1D)

• IEEE-802.1D standard provides Layer 2 prioritization within the LAN

• IP ToS will be used for prioritization across the WAN

• RSVP appears to be dying a peaceful death

L3

L2

L2

L2

L3

Receiver

Sender

L2

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