QinQ报文帧格式

QinQ报文帧格式

QinQ是对802.1Q（VLAN）的扩展，其核心思想是将用户私网VLAN tag封装到公网VLAN tag中，报文带着两层tag穿越服务商的骨干网络，从而为用户提供一种较为简单的二层VPN隧道。QinQ报文有固定的格式，就是在802.1Q的标签之上再打一层802.1Q标签，QinQ报文比802.1Q（VLAN）报文多4字节。

一、 QinQ报文帧格式

+-----------+-----------+-----------+-----------+-------------+------------------+----------+

+-----------+-----------+-----------+-----------+-------------+------------------+----------+

| |

| | |

+-----------+-----------+-----------+-----------+-----------+-----------+-------------+------------------+----------+

+-----------+-----------+-----------+-----------+-----------+-----------+-------------+------------------+----------+

| | |

+-----------+--------------+---------+--------------+

| 0x8100 | Priority | CFI | VLAN ID |

字段	长度	含义
DMAC	6字节	目的MAC地址，该字段标识帧的接收者。
SMAC	6字节	源MAC地址，该字段标识帧的发送者。
TPID	2字节	TPID（Tag Protocol Identifier，标签协议标识）表示帧类型。取值为0x8100时表示802.1Q Tag帧。如果不支持802.1Q的设备收到这样的帧，会将其丢弃。对于内层的802.1Q Tag，该值设置为0x8100；对于外层的802.1Q Tag，不同厂商所使用的值可能不相同： · 0x8100：Huawei路由器使用 · 0x88A8：802.1ad规定外层802.1Q Tag中的TPID为0x88a8 · 0x9100：Juniper路由器使用 · 0x9200：Several路由器使用在使用VRP®（Versatile Routing Platform）软件的华为设备上，外层802.1Q Tag缺省情况下值为0x8100，可以通过命令行调整该值。
PRI	3比特	Priority，长度为3比特，表示帧的优先级，取值范围为0～7，值越大优先级越高。当网络拥塞时，优先级高的数据包优先发送。
CFI/DEI	1比特	CFI (Canonical Format Indicator，标准格式指示)，长度为1比特，表示MAC地址是否是标准格式。CFI为0说明是标准格式（以太网帧的MAC地址采用低字节在前），CFI为1表示为非标准格式（以太网帧的MAC地址采用高字节在前）。CFI可用于区分以太网帧、FDDI（Fiber Distributed Digital Interface）帧和令牌环网帧。在以太网中，CFI的值为0。 DEI（Drop Eligible Indicator，丢弃优先级指示），配合PRI字段使用，共同指示帧的丢弃优先级，也就是系统发生了拥塞时，这些报文会被优先丢弃。说明： IEEE 802.1Q定义了CFI字段，而IEEE 802.1ad标准重新定义了CFI字段，规定S-Tag里面的是DEI，C-Tag里面的是CFI。实际应用中，可以根据需要将此比特位用作CFI或者用作DEI。
VID	12比特	VID（LAN ID），长度为12比特，表示该帧所属的VLAN。在使用VRP®（Versatile Routing Platform）软件的华为设备上，可配置的VLAN ID取值范围为1～4094。协议规定0和4095为保留的VLAN ID。
Length/Type	2字节	该字段有两种含义： · Length：如果该字段值小于或等于二进制1500（或十六进制0x05DC）时，该字段指后续数据的字节长度，但不包括FCS字段。 · Type：如果该字段值大于或等于二进制1536（或十六进制0x0600）时，该字段指链路直接封装的上层协议类型。
Data	-38～1500字节	QinQ帧的负载（可能包含填充位）。 QinQ帧的长度必须为整数字节，因此帧的负载长度不足整数字节，需插入填充字段以保证数据帧的长度为整数字节。说明： IEEE 802.1Q和IEEE 802.1ad标准中并没有定义QinQ帧的最小长度和最大长度。
CRC	4字节	帧校验序列FCS（Frame Check Sequence）是为接收网卡提供判断是否传输错误的一种方法，如果发现错误，丢弃此帧。 FCS只是通用叫法，具体的FCS还可以细分多种校验方法。在以太帧中，FCS通常采用循环冗余码校验CRC（Cyclical Redundancy Check）。

二、QinQ报文帧示例

Frame 1: 391 bytes on wire (3128 bits), 391 bytes captured (3128 bits)
    Arrival Time: Nov 17, 2011 18:52:25.161695000 
    Epoch Time: 1321527145.161695000 seconds
    [Time delta from previous captured frame: 0.000000000 seconds]
    [Time delta from previous displayed frame: 0.000000000 seconds]
    [Time since reference or first frame: 0.000000000 seconds]
    Frame Number: 1
    Frame Length: 391 bytes (3128 bits)
    Capture Length: 391 bytes (3128 bits)
    [Frame is marked: False]
    [Frame is ignored: False]
    [Protocols in frame: eth:ip:udp:bootp]
    [Coloring Rule Name: UDP]
    [Coloring Rule String: udp]
Ethernet II (VLAN tagged), Src: HuaweiTe_75:ad:21 (54:89:98:75:ad:21), Dst: RealtekS_88:35:39 (00:e0:4c:88:35:39)
    Destination: RealtekS_88:35:39 (00:e0:4c:88:35:39)
        Address: RealtekS_88:35:39 (00:e0:4c:88:35:39)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
    Source: HuaweiTe_75:ad:21 (54:89:98:75:ad:21)
        Address: HuaweiTe_75:ad:21 (54:89:98:75:ad:21)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
    VLAN tag: VLAN=100, Priority=Controlled Load
        Identifier: 802.1Q Virtual LAN (0x8100)
        100. .... .... .... = Priority: Controlled Load (4)
        ...0 .... .... .... = CFI: Canonical (0)
        .... 0000 0110 0100 = VLAN: 100
    VLAN tag: VLAN=200, Priority=Controlled Load
        Identifier: 802.1Q Virtual LAN (0x8100)
        100. .... .... .... = Priority: Controlled Load (4)
        ...0 .... .... .... = CFI: Canonical (0)
        .... 0000 1100 1000 = VLAN: 200
    Type: IP (0x0800)
Internet Protocol Version 4, Src: 192.168.112.1 (192.168.112.1), Dst: 192.168.112.100 (192.168.112.100)
    Version: 4
    Header length: 20 bytes
    Differentiated Services Field: 0x80 (DSCP 0x20: Class Selector 4; ECN: 0x00: Not-ECT (Not ECN-Capable Transport))
        1000 00.. = Differentiated Services Codepoint: Class Selector 4 (0x20)
        .... ..00 = Explicit Congestion Notification: Not-ECT (Not ECN-Capable Transport) (0x00)
    Total Length: 369
    Identification: 0x8ab5 (35509)
    Flags: 0x00
        0... .... = Reserved bit: Not set
        .0.. .... = Don't fragment: Not set
        ..0. .... = More fragments: Not set
    Fragment offset: 0
    Time to live: 16
    Protocol: UDP (17)
    Header checksum: 0xbc90 [correct]
        [Good: True]
        [Bad: False]
    Source: 192.168.112.1 (192.168.112.1)
    Destination: 192.168.112.100 (10.168.112.100)
User Datagram Protocol, Src Port: bootps (67), Dst Port: bootps (67)
    Source port: bootps (67)
    Destination port: bootps (67)
    Length: 349
    Checksum: 0x0000 (none)
        [Good Checksum: False]
        [Bad Checksum: False]
Bootstrap Protocol
    Message type: Boot Request (1)
    Hardware type: Ethernet
    Hardware address length: 6
    Hops: 1
    Transaction ID: 0x7a31a29f
    Seconds elapsed: 0
    Bootp flags: 0x0000 (Unicast)
        0... .... .... .... = Broadcast flag: Unicast
        .000 0000 0000 0000 = Reserved flags: 0x0000
    Client IP address: 0.0.0.0 (0.0.0.0)
    Your (client) IP address: 0.0.0.0 (0.0.0.0)
    Next server IP address: 0.0.0.0 (0.0.0.0)
    Relay agent IP address: 100.1.1.1 (100.1.1.1)
    Client MAC address: IntelCor_7b:75:58 (00:27:10:7b:75:58)
    Client hardware address padding: 00000000000000000000
    Server host name not given
    Boot file name not given
    Magic cookie: DHCP
    Option: (t=53,l=1) DHCP Message Type = DHCP Discover
        Option: (53) DHCP Message Type
        Length: 1
        Value: 01
    Option: (t=116,l=1) DHCP Auto-Configuration = AutoConfigure
        Option: (116) DHCP Auto-Configuration
        Length: 1
        Value: 01
    Option: (t=61,l=7) Client identifier
        Option: (61) Client identifier
        Length: 7
        Value: 010027107b7558
        Hardware type: Ethernet
        Client MAC address: IntelCor_7b:75:58 (00:27:10:7b:75:58)
    Option: (t=50,l=4) Requested IP Address = 169.254.145.113
        Option: (50) Requested IP Address
        Length: 4
        Value: a9fe9171
    Option: (t=12,l=13) Host Name = "cda101059953g"
        Option: (12) Host Name
        Length: 13
        Value: 63646131303130353939353367
    Option: (t=60,l=8) Vendor class identifier = "MSFT 5.0"
        Option: (60) Vendor class identifier
        Length: 8
        Value: 4d53465420352e30
    Option: (t=55,l=11) Parameter Request List
        Option: (55) Parameter Request List
        Length: 11
        Value: 010f03062c2e2f1f21f92b
        1 = Subnet Mask
        15 = Domain Name
        3 = Router
        6 = Domain Name Server
        44 = NetBIOS over TCP/IP Name Server
        46 = NetBIOS over TCP/IP Node Type
        47 = NetBIOS over TCP/IP Scope
        31 = Perform Router Discover
        33 = Static Route
        249 = Private/Classless Static Route (Microsoft)
        43 = Vendor-Specific Information
    Option: (t=43,l=2) Vendor-Specific Information
        Option: (43) Vendor-Specific Information
        Length: 2
        Value: dc00
    Option: (t=82,l=35) Agent Information Option
        Option: (82) Agent Information Option
        Length: 35
        Value: 010c303330422d303030302d474502134855415745492d30...
        Agent Circuit ID: 303330422d303030302d4745
        Agent Remote ID: 4855415745492d303330422d303030302d4745
    End Option

三、QinQ帧参考标准

标准	描述
RFC 3069	VLAN Aggregation for Efficient IP Address Allocation
IEEE 802.1Q	IEEE Standards for Local and Metropolitan Area Networks : Virtual Bridged Local Area Networks
IEEE 802.1ad	IEEE Standards for Local and Metropolitan Area Networks: Virtual Bridged Local Area Networks- Amendment 4

二、QinQ报文帧示例

三、QinQ帧参考标准

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