802.1 vLAN meeting, 3/12/96, 11:20pm, LaJolla, Ca.
2-Layer
presentation, Norm Finn - CISCO

one-layer

two layer
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Common Considerations
-Simplifying assumption: One packet format on one LAN segment per vLAN.
-"Edge switches" translate between tagged and untagged fromats.
-"Fabric switches" transfer tagger packets
-One packet switch may display both Edge and Fabric bahaviors.
-MAC layer over which tagged packets flow is unchanged.
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One-layer Model
DA SA Ethertype=x VLAN-ID    ...Remainder of original frame... new FCS
6  6      2         2
-Ethertype marks packet as tagged.
-vLAN-ID identifies vLAN to shich packet belongs
-Features that require fabric switches to pay attention to vLAN-ID:
  -MAC addresses duplicated in different vLANs
  -Per-vLAN spanning tree blocking on same port
-Where vLAN-ID matters, switches use(vLAN-ID, MAC address) pairs,
  instead of (MAC address), for bridging.
-Otherwise, swithces operates same as mofmal transparent bridge.
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TWO LAYER MODEL
vDest vSource Ethertype=y VLAN-ID CRC fix   ... original frame with FCS
6      6      2            2        4
-vDEST, vSource are MAC addresses of switches.
-Ethertype markes packet as tagges (different from one-layer Ethertype).
-vLAN-ID identifies vLAN to which packet belongs
CRC fix chosen to give original and tagged packet same CRC.
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Two-layer Model - Unicast Forwarding
-If tagged vDEST == "not for me", forward packet on Fabric LAN.
  -Original Dest and Source MAC addresses may be ignored.
  -original Source MAC address information may be learned.
If tagged vDEST == "for me", assign packet to vLAN from vlaniID in tag.




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