Frame Tagging on trunk link

johnny_jiang

               
                                                Frame Tagging
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1. ISL - Inter-switch Link
2. 802.1Q
ISL
802.1Q
cisco proprietary
open standard
encapsulate frame
tagg frame
protocol independent
dependent (ehter, token ring)
new frame (30 bytes)
4-byte field inserted
PVST
common STP, multiple STP, rapid STP
unawared: drop
unawared: tag ignored, recognized
1024 VLAN
4096 VLAN
no native VLAN
native VLAN
1518 Native VLAN
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A trunk port will support only one native active VLAN per operational mode. The modes are access and trunk.

By default, on Cisco Catalyst switches, all switch ports and native VLANs for 802.1Q are assigned to VLAN1.

The 802.1Q trunk ports connected to each other via physical or logical segments must all have the same native VLAN configured to operate correctly.

If the native VLAN is misconfigured for trunk ports on the same trunk link, Layer 2 loops can occur due to diverting Spanning Tree Protocol (STP) BPDUs from their correct VLAN.
Dynamic Trunking Protocol
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DTP is cisco proprietary. When using this protocol, since it will carry VTP domain information, if it's not identical on both side, trunk link cannot be established. Thus, use command 'swithport nonegotiate' to disable DTP.
               
               
               
               
               
               
               
               
               
               
               

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