INE R&S ATC003 - Ethernet Overview, Layer 2 Switchports, Trunking, ISL, 802.1q, DTP

Separate “core” network tasks from “peripheral” tasks

Core tasks
- 100% needed for basic layer 2 connectivity
- Cannot do anything layer 3+ without this

Peripheral tasks
- Rest of layer 3+ tasks do not rely on these topics

Core Ethernet Switching
- Trunking
- VLANs
- VTP
- EtherChannel
- 802.1q Tunneling (Possibly Core)

Peripheral Ethernet Switching
Everything else
- STP
- Layer 2 Security
- Layer 2 QoS

Ethernet Interface Types
- Layer 2 Switchports
-- Access (One VLAN)
-- Trunk (Multiple VLANs)
-- Tunnel (Transparent Layer 2 VPN)
-- Dynamic (DTP Negotiation)

- Layer 3 Ports
-- Switched Virtual Interface (SVI)
-- Native Routed Interfaces

ISL
- Cisco proprietary
- All traffic encapsulated with ISL

802.1q
- Open standard
- "Native" VLAN sent untagged (可以用vlan dot1q tag native讓native vlan送tag)

DTP
- Dynamic Trunking Protocol

DTP Negotiation (Enabled by default)

- Desirable mode (Initiates trunking negotiation)
-- switchport mode dynamic desirable
-- switchport mode trunk (需要先下switchport trunk encapsulation dot1q/isl,才能下mode trunk)

- Auto mode (Passively listen for trunking negotiation)
-- switchport mode dynamic auto

DisablingDTP Negotiation
- switchport nonegotiate
- switchport mode access
- switchport mode dot1q-tunnel

Verified with…
- show interface trunk
- show interface switchport
- show spanning-tree[vlan | interface]

兩邊SW的設定如下時...Trunking會起來
Desirable Desirable
Desirable Auto
Desirable ON
ON          ON
ON          AUTO
其他則無法連通