「VXLAN」- TYPE-2-ROUTE：Host MAC-ADDR Advertisement

  CREATED BY JENKINSBOT

其用于同子网主机互访场景下进行主机 MAC 地址通告，包含主机 MAC 信息和二层 VNI：

报文结构

报文示例（Wirkshark）

Border Gateway Protocol - UPDATE Message
    Marker: ffffffffffffffffffffffffffffffff
    Length: 112
    Type: UPDATE Message (2)
    Withdrawn Routes Length: 0
    Total Path Attribute Length: 89
    Path attributes
        Path Attribute - ORIGIN: INCOMPLETE
        Path Attribute - AS_PATH: empty
        Path Attribute - LOCAL_PREF: 100
        Path Attribute - EXTENDED_COMMUNITIES
            Flags: 0xc0, Optional, Transitive, Complete
                1... .... = Optional: Set
                .1.. .... = Transitive: Set
                ..0. .... = Partial: Not set
                ...0 .... = Extended-Length: Not set
                .... 0000 = Unused: 0x0
            Type Code: EXTENDED_COMMUNITIES (16)
            Length: 24
            Carried extended communities: (3 communities)
                Route Target: 742:1 [Transitive 2-Octet AS-Specific]
                    Type: Transitive 2-Octet AS-Specific (0x00)
                        0... .... = IANA Authority: Allocated on Standard Action, Early Allocation or Experimental Basis
                        .0.. .... = Transitive across AS: Transitive
                    Subtype (AS2): Route Target (0x02)
                    2-Octet AS: 742
                    4-Octet AN: 1
                Encapsulation: VXLAN Encapsulation [Transitive Opaque]
                    Type: Transitive Opaque (0x03)
                        0... .... = IANA Authority: Allocated on Standard Action, Early Allocation or Experimental Basis
                        .0.. .... = Transitive across AS: Transitive
                    Subtype (Opaque): Encapsulation (0x0c)
                    Tunnel type: VXLAN Encapsulation (8)
                MAC Mobility: Sticky MAC [Transitive EVPN]
                    Type: Transitive EVPN (0x06)
                        0... .... = IANA Authority: Allocated on Standard Action, Early Allocation or Experimental Basis
                        .0.. .... = Transitive across AS: Transitive
                    Subtype (EVPN): MAC Mobility (0x00)
                    Flags: 0x01
                        .... ...1 = Sticky/Static MAC: Yes
                    Sequence number: 0
        Path Attribute - MP_REACH_NLRI
            Flags: 0x90, Optional, Extended-Length, Non-transitive, Complete
                1... .... = Optional: Set
                .0.. .... = Transitive: Not set
                ..0. .... = Partial: Not set
                ...1 .... = Extended-Length: Set
                .... 0000 = Unused: 0x0
            Type Code: MP_REACH_NLRI (14)
            Length: 44
            Address family identifier (AFI): Layer-2 VPN (25)
            Subsequent address family identifier (SAFI): EVPN (70)
            Next hop: 10.0.0.1
                IPv4 Address: 10.0.0.1
            Number of Subnetwork points of attachment (SNPA): 0
            Network Layer Reachability Information (NLRI)
                EVPN NLRI: MAC Advertisement Route
                    Route Type: MAC Advertisement Route (2)
                    Length: 33
                    Route Distinguisher: 000002e600000001 (742:1)
                    ESI: 00:00:00:00:00:00:00:00:00:00
                        ESI Type: ESI 9 bytes value (0)
                        ESI Value: 00 00 00 00 00 00 00 00 00
                        ESI 9 bytes value: 00 00 00 00 00 00 00 00 00
                    Ethernet Tag ID: 0
                    MAC Address Length: 48
                    MAC Address: HuaweiTe_17:6c:c6 (70:7b:e8:17:6c:c6)
                    IP Address Length: 0
                    IP Address: NOT INCLUDED
                        [Expert Info (Note/Protocol): IP Address: NOT INCLUDED]
                            [IP Address: NOT INCLUDED]
                            [Severity level: Note]
                            [Group: Protocol]
                    VNI: 6731

MP_REACH_NLRI

我们重点关注在 NLRI 中的字段：

Route Distinguisher
Ethernet Segment Identifier
Ethernet Tag ID
MAC Address Length = Length of MAC-ADDR
MAC Address = MAC-ADDR
IP Address Length
IP Address
MPLS Label1 = LAYER-2-VNI
MPLS Label2

场景：同子网互访

所示如图，BGP EVPN 通过 TYPE-2-ROUTE 完成 MAC-ADDR 动态学习，以实现 VXLAN 同子网互访；

同子网主机 MAC-ADDR 通告：

PC1 产生数据流量并发往 SW1；

SW1 获知 PC1 的 MAC-ADDR，它在 MAC-ADDR-TAB 中创建一个表项，记录该 MAC-ADDR、BD-ID、入接口；
SW1 根据该表项生成 BGP EVPN ROUTE 并发送给 SW2 设备。该路由携带本端 EVPN-Inst 的 RT 值（Path-Attr.Ext-Cmty.RT）以及 TYPE-2-ROUTE（ MAC-ROUTE）。在 MAC ROUTE 中，PC1 的 MAC-ADDR 存放在 MAC Address 字段中，LAYER-2-VNI 存放在 MPLS Label1 字段中；

SW2 收到 SW1 发来的 BGP EVPN ROUTE 后：
1）首先，检查其携带的 RT（类似 MPLS VPN 的 RT 的概念），如果与本端 EVPN 实例的入站 RT 相等，则接收该路由，否则丢弃；
2）在接收该路由后，SW2 获得 PC1 的 MAC-ADDR、BD-ID 和 SW1.VTEP-IP-ADDR（MP_REACH_NLRI.Next-hop-network-address 携带）的对应关系，并在本地的 MAC-ADDR-TAB 中生成对应表项，其出接口需根据下一跳进行迭代，最终迭代结果是指向 SW1 的 VXLAN 隧道；

补充说明

在 eNSP 中，我们进行同网段互通实验，我们并没有观察到该类型路由通告。但是，在跨网段互通实验中，我们观察到网关发送包含 Vbdif MAC-ADDR 的 TYPE-2-ROUTE 给同网段内的设备；