L2PT (Layer 2 Protocol Tunneling)

L2PT

Layer 2 Protocol Tunneling

這其實是為了解決edge端switch在跑Layer 2 protocol時候發出很多BPDU的同時，在Service Provider的core-network也會有對應的Layer 2 protocol在run，為了不讓彼此互相干擾所衍生的tunneling feature

Layer 2 Protocol Tunneling Network Configuration, from Reference[1]

以這圖而言，Switch 1 2 3 以及4 5 的Layer 2 protocol就可以互通，然後不影響Service Provider的Layer 2 protocol

port role可分成access port以及tunnel port

access port代表接edge switch的port，當這個port收到特定BPDU時會把它封裝成帶特定MAC(user可自己設定)然後送往tunnel port往core-network丟

tunnel port代表接core-network的port，當這個port收到帶特定MAC的packet會把它解封裝然後丟回access port

目前常見support的Layer 2 feature有STP, CDP, VTP, PAgP, and UDLD
扣除STP (Spanning Tree Protocol)外，CDP (Cisco Discovery Protocol), VTP (VLAN Trunking Protocol), PAgP (Port Aggregation Protocol), UDLD (Uni-Directional Link Direction)都是CISCO自己提出的protocol

Reference:

[1] http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SXF/native/configuration/guide/l2pt.html

[2] http://guiderworld.blogspot.com/2009/02/layer-2-protocol-tunneling.html