# DTP（DynamicTrunking protocol）是思科私有協議為Trunk服務，前身是DISL。可以讓交換機間的鏈路自動協商是否形成Trunk。
# TRUNK介紹過配置Trunk用switchporttrunk encapsulation dot1Q和switchportmode trunk這兩條命令即可。
# 現在可以不用手動打這兩條命令，而是用DTP來自動協商形成Trunk。另外DTP還可以協商Trunk鏈路的封裝類型（802.1Q或ISL）。配置了DTP的交換機會發送DTP協商包，對方對DTP協商包進行響應，最終決定是否可以形成Trunk。
# 30s發送一次DTP的frame. 該協議僅在交換機間協商。

# DTP有4種模式分別是：auto，dersirable，trunk negotiate，trunk nonegotiate
# auto：被動協商，不主動發送DTP，但收到DTP後可以回復，回復後成功協商成Trunk鏈路
# desirable：期望把接口置於Trunk模式，會主動發送或回復DTP協商，只要對方能響應，就成功協商成Trunk鏈路
# negotiate：已經強制將端口配成Trunk模式了，會主動發送或回復DTP協商，只要對方能響應，就成功協商成Trunk鏈路
# nonegotiate：已經強制將端口配成Trunk模式了，但不主動發送或回復DTP協商。因此只有在對方端口已經是negotiate或nonegotiate，即對方端口已經配置成了Trunk的情況下，才能形成Trunk鏈路

--------------------------------------------------------------------
        |         SW1         |      |         SW2         | 
        |        trunk        |  --  |        trunk        |  
        |        none         |      |        none         |
--------------------------------------------------------------------      
                
IOU1(config)#do sh int e3/3 swi
Name: Et3/3
Switchport: Enabled
Administrative Mode: dynamic desirable
Operational Mode: trunk
Administrative Trunking Encapsulation: negotiate
Operational Trunking Encapsulation: isl
Negotiation of Trunking: On
Access Mode VLAN: 1 (default)
Trunking Native Mode VLAN: 1 (default)
Administrative Native VLAN tagging: enabled
Voice VLAN: none
Administrative private-vlan host-association: none 
Administrative private-vlan mapping: none 
Administrative private-vlan trunk native VLAN: none
Administrative private-vlan trunk Native VLAN tagging: enabled
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk associations: none
Administrative private-vlan trunk mappings: none
Operational private-vlan: none
Trunking VLANs Enabled: ALL
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Capture VLANs Allowed: ALL
Appliance trust: none
IOU1(config)#

IOU2(config)#do sh int e3/3 swi
Name: Et3/3
Switchport: Enabled
Administrative Mode: dynamic desirable
Operational Mode: trunk
Administrative Trunking Encapsulation: negotiate
Operational Trunking Encapsulation: isl
Negotiation of Trunking: On
Access Mode VLAN: 1 (default)
Trunking Native Mode VLAN: 1 (default)
Administrative Native VLAN tagging: enabled
Voice VLAN: none
Administrative private-vlan host-association: none 
Administrative private-vlan mapping: none 
Administrative private-vlan trunk native VLAN: none
Administrative private-vlan trunk Native VLAN tagging: enabled
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk associations: none
Administrative private-vlan trunk mappings: none
Operational private-vlan: none
Trunking VLANs Enabled: ALL
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Capture VLANs Allowed: ALL
Appliance trust: none
IOU2(config)#

Frame 5064: 60 bytes on wire (480 bits), 60 bytes captured (480 bits) on interface 0
Ethernet II, Src: aa:bb:cc:00:04:33 (aa:bb:cc:00:04:33), Dst: CDP/VTP/DTP/PAgP/UDLD (01:00:0c:cc:cc:cc)
    Destination: CDP/VTP/DTP/PAgP/UDLD (01:00:0c:cc:cc:cc)       # 目的MAC地址 CDP/VTP/DTP/PAgP/UDLD (01:00:0c:cc:cc:cc) 
    Source: aa:bb:cc:00:04:33 (aa:bb:cc:00:04:33)
    Type: 802.1Q Virtual LAN (0x8100)
802.1Q Virtual LAN, PRI: 0, CFI: 0, ID: 1
    000. .... .... .... = Priority: Best Effort (default) (0)
    ...0 .... .... .... = CFI: Canonical (0)
    .... 0000 0000 0001 = ID: 1                                  # 802.1Q封裝 vlan 1  
    Length: 34
    Padding: 0000000000000000
Logical-Link Control
    DSAP: SNAP (0xaa)
        1010 101. = SAP: SNAP
        .... ...0 = IG Bit: Individual
    SSAP: SNAP (0xaa)
        1010 101. = SAP: SNAP
        .... ...0 = CR Bit: Command
    Control field: U, func=UI (0x03)
        000. 00.. = Command: Unnumbered Information (0x00)
        .... ..11 = Frame type: Unnumbered frame (0x3)
    Organization Code: Cisco (0x00000c)                          # cisco 私有協議  
    PID: DTP (0x2004)                                            # 采用DTP協議
Dynamic Trunk Protocol:  (Operating/Administrative): Trunk/Desirable (0x83) (Operating/Administrative): ISL/Negotiated (0x40): aa:bb:cc:00:04:33
    Version: 1
    Domain
        Type: Domain (0x0001)
        Length: 5
        Domain: 
    Trunk Status
        Type: Trunk Status (0x0002)
        Length: 5
        Value: Trunk/Desirable (0x83)                            # Trunk Status ：Trunk/Desirable 模式
            1... .... = Trunk Operating Status: Trunk (0x1)
            .... .011 = Trunk Administrative Status: Desirable (0x3)
    Trunk Type
        Type: Trunk Type (0x0003)
        Length: 5
        Value: ISL/Negotiated (0x40)                             
            010. .... = Trunk Operating Type: ISL (0x2)                # trunk 類型為 ISL
            .... .000 = Trunk Administrative Type: Negotiated (0x0)    # 管理配置類型：Negotiated
    Sender ID
        Type: Sender ID (0x0004)
        Length: 10
        Sender ID: aa:bb:cc:00:04:33 (aa:bb:cc:00:04:33)
        
Frame 5065: 60 bytes on wire (480 bits), 60 bytes captured (480 bits) on interface 0
Ethernet II, Src: aa:bb:cc:00:06:33 (aa:bb:cc:00:06:33), Dst: CDP/VTP/DTP/PAgP/UDLD (01:00:0c:cc:cc:cc)
    Destination: CDP/VTP/DTP/PAgP/UDLD (01:00:0c:cc:cc:cc)        # 目的MAC地址 CDP/VTP/DTP/PAgP/UDLD (01:00:0c:cc:cc:cc)
    Source: aa:bb:cc:00:06:33 (aa:bb:cc:00:06:33)
    Type: 802.1Q Virtual LAN (0x8100)
802.1Q Virtual LAN, PRI: 0, CFI: 0, ID: 1
    000. .... .... .... = Priority: Best Effort (default) (0)
    ...0 .... .... .... = CFI: Canonical (0)
    .... 0000 0000 0001 = ID: 1
    Length: 34
    Padding: 0000000000000000
Logical-Link Control
    DSAP: SNAP (0xaa)
        1010 101. = SAP: SNAP
        .... ...0 = IG Bit: Individual
    SSAP: SNAP (0xaa)
        1010 101. = SAP: SNAP
        .... ...0 = CR Bit: Command
    Control field: U, func=UI (0x03)
        000. 00.. = Command: Unnumbered Information (0x00)
        .... ..11 = Frame type: Unnumbered frame (0x3)
    Organization Code: Cisco (0x00000c)
    PID: DTP (0x2004)
Dynamic Trunk Protocol:  (Operating/Administrative): Trunk/Desirable (0x83) (Operating/Administrative): ISL/Negotiated (0x40): aa:bb:cc:00:06:33
    Version: 1
    Domain
        Type: Domain (0x0001)
        Length: 5
        Domain: 
    Trunk Status
        Type: Trunk Status (0x0002)
        Length: 5
        Value: Trunk/Desirable (0x83)
            1... .... = Trunk Operating Status: Trunk (0x1)
            .... .011 = Trunk Administrative Status: Desirable (0x3)
    Trunk Type
        Type: Trunk Type (0x0003)
        Length: 5
        Value: ISL/Negotiated (0x40)
            010. .... = Trunk Operating Type: ISL (0x2)
            .... .000 = Trunk Administrative Type: Negotiated (0x0)
    Sender ID
        Type: Sender ID (0x0004)
        Length: 10
        Sender ID: aa:bb:cc:00:06:33 (aa:bb:cc:00:06:33)
        
        
--------------------------------------------------------------------------------------------------
        |                 SW1                 |      |                 SW2                 | 
        |                trunk                |  --  |                trunk                | 
        |switchport trunk encapsulation dot1q |      |switchport trunk encapsulation dot1q |
        |       switchport mode trunk         |      |       switchport mode trunk         | 
--------------------------------------------------------------------------------------------------

IOU1(config-if)#do sh int e3/3 swi
Name: Et3/3
Switchport: Enabled
Administrative Mode: trunk
Operational Mode: trunk
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: On
Access Mode VLAN: 1 (default)
Trunking Native Mode VLAN: 1 (default)
Administrative Native VLAN tagging: enabled
Voice VLAN: none
Administrative private-vlan host-association: none 
Administrative private-vlan mapping: none 
Administrative private-vlan trunk native VLAN: none
Administrative private-vlan trunk Native VLAN tagging: enabled
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk associations: none
Administrative private-vlan trunk mappings: none
Operational private-vlan: none
Trunking VLANs Enabled: ALL
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Capture VLANs Allowed: ALL
Appliance trust: none
IOU1(config-if)#

IOU2(config-if)#do sh int e3/3 swi
Name: Et3/3
Switchport: Enabled
Administrative Mode: trunk
Operational Mode: trunk
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: On
Access Mode VLAN: 1 (default)
Trunking Native Mode VLAN: 1 (default)
Administrative Native VLAN tagging: enabled
Voice VLAN: none
Administrative private-vlan host-association: none 
Administrative private-vlan mapping: none 
Administrative private-vlan trunk native VLAN: none
Administrative private-vlan trunk Native VLAN tagging: enabled
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk associations: none
Administrative private-vlan trunk mappings: none
Operational private-vlan: none
Trunking VLANs Enabled: ALL
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Capture VLANs Allowed: ALL
Appliance trust: none
IOU2(config-if)#

Frame 6159: 60 bytes on wire (480 bits), 60 bytes captured (480 bits) on interface 0
Ethernet II, Src: aa:bb:cc:00:06:33 (aa:bb:cc:00:06:33), Dst: CDP/VTP/DTP/PAgP/UDLD (01:00:0c:cc:cc:cc)
    Destination: CDP/VTP/DTP/PAgP/UDLD (01:00:0c:cc:cc:cc)
    Source: aa:bb:cc:00:06:33 (aa:bb:cc:00:06:33)
    Type: 802.1Q Virtual LAN (0x8100)
802.1Q Virtual LAN, PRI: 0, CFI: 0, ID: 1
    000. .... .... .... = Priority: Best Effort (default) (0)
    ...0 .... .... .... = CFI: Canonical (0)
    .... 0000 0000 0001 = ID: 1
    Length: 34
    Padding: 0000000000000000
Logical-Link Control
    DSAP: SNAP (0xaa)
        1010 101. = SAP: SNAP
        .... ...0 = IG Bit: Individual
    SSAP: SNAP (0xaa)
        1010 101. = SAP: SNAP
        .... ...0 = CR Bit: Command
    Control field: U, func=UI (0x03)
        000. 00.. = Command: Unnumbered Information (0x00)
        .... ..11 = Frame type: Unnumbered frame (0x3)
    Organization Code: Cisco (0x00000c)
    PID: DTP (0x2004)
Dynamic Trunk Protocol:  (Operating/Administrative): Trunk/On (0x81) (Operating/Administrative): 802.1Q/802.1Q (0xa5): aa:bb:cc:00:06:33
    Version: 1
    Domain
        Type: Domain (0x0001)
        Length: 5
        Domain: 
    Trunk Status
        Type: Trunk Status (0x0002)
        Length: 5
        Value: Trunk/On (0x81)
            1... .... = Trunk Operating Status: Trunk (0x1)              # 
            .... .001 = Trunk Administrative Status: On (0x1)
    Trunk Type
        Type: Trunk Type (0x0003)
        Length: 5
        Value: 802.1Q/802.1Q (0xa5)
            101. .... = Trunk Operating Type: 802.1Q (0x5)               # Trunk Type : 802.1Q 
            .... .101 = Trunk Administrative Type: 802.1Q (0x5)          # 管理配置類型: 802.1Q         
    Sender ID
        Type: Sender ID (0x0004)
        Length: 10
        Sender ID: aa:bb:cc:00:06:33 (aa:bb:cc:00:06:33)
        
Frame 6160: 60 bytes on wire (480 bits), 60 bytes captured (480 bits) on interface 0
Ethernet II, Src: aa:bb:cc:00:04:33 (aa:bb:cc:00:04:33), Dst: CDP/VTP/DTP/PAgP/UDLD (01:00:0c:cc:cc:cc)
    Destination: CDP/VTP/DTP/PAgP/UDLD (01:00:0c:cc:cc:cc)
    Source: aa:bb:cc:00:04:33 (aa:bb:cc:00:04:33)
    Type: 802.1Q Virtual LAN (0x8100)
802.1Q Virtual LAN, PRI: 0, CFI: 0, ID: 1
    000. .... .... .... = Priority: Best Effort (default) (0)
    ...0 .... .... .... = CFI: Canonical (0)
    .... 0000 0000 0001 = ID: 1
    Length: 34
    Padding: 0000000000000000
Logical-Link Control
    DSAP: SNAP (0xaa)
        1010 101. = SAP: SNAP
        .... ...0 = IG Bit: Individual
    SSAP: SNAP (0xaa)
        1010 101. = SAP: SNAP
        .... ...0 = CR Bit: Command
    Control field: U, func=UI (0x03)
        000. 00.. = Command: Unnumbered Information (0x00)
        .... ..11 = Frame type: Unnumbered frame (0x3)
    Organization Code: Cisco (0x00000c)
    PID: DTP (0x2004)
Dynamic Trunk Protocol:  (Operating/Administrative): Trunk/On (0x81) (Operating/Administrative): 802.1Q/802.1Q (0xa5): aa:bb:cc:00:04:33
    Version: 1
    Domain
        Type: Domain (0x0001)
        Length: 5
        Domain: 
    Trunk Status
        Type: Trunk Status (0x0002)
        Length: 5
        Value: Trunk/On (0x81)
            1... .... = Trunk Operating Status: Trunk (0x1)
            .... .001 = Trunk Administrative Status: On (0x1)
    Trunk Type
        Type: Trunk Type (0x0003)
        Length: 5
        Value: 802.1Q/802.1Q (0xa5)
            101. .... = Trunk Operating Type: 802.1Q (0x5)
            .... .101 = Trunk Administrative Type: 802.1Q (0x5)
    Sender ID
        Type: Sender ID (0x0004)
        Length: 10
        Sender ID: aa:bb:cc:00:04:33 (aa:bb:cc:00:04:33)

DTP 抓包分析