在Kompella <VPN_name>.l2vpn.0 VPN情况下，Juniper如何将CE中的帧与正确的路由相关联？

Question

假设，我有以下简单的BGP信号L2VPN配置：

root@PE4> show configuration routing-instances
vpn-b {
    instance-type l2vpn;
    interface ge-0/0/0.515;
    route-distinguisher 65512:200;
    vrf-target target:65512:200;
    protocols {
        l2vpn {
            encapsulation-type ethernet-vlan;
            site ce-d {
                site-identifier 2;
                interface ge-0/0/0.515;
            }
        }
    }
}

root@PE4>

vpn-b.l2vpn.0表的内容如下所示：

root@PE4> show route table vpn-b.l2vpn.0 detail

vpn-b.l2vpn.0: 2 destinations, 2 routes (2 active, 0 holddown, 0 hidden)
 65512:200:1:1/96 (1 entry, 1 announced)
        *BGP    Preference: 170/-101
                Route Distinguisher: 65512:200
                Next hop type: Indirect, Next hop index: 0
                Address: 0xce2eb90
                Next-hop reference count: 6
                Source: 192.168.2.1
                Protocol next hop: 192.168.2.1
                Indirect next hop: 0x2 no-forward INH Session ID: 0x0
                State: <Secondary Active Int Ext>
                Local AS: 65512 Peer AS: 65512
                Age: 3:29:45    Metric2: 1
                Validation State: unverified
                Task: BGP_65512.192.168.2.1+179
                Announcement bits (1): 0-vpn-b-l2vpn
                AS path: I
                Communities: target:65512:200 Layer2-info: encaps: VLAN, control flags:[0x2] Control-Word, mtu: 0, site preference: 100
                Import Accepted
                Label-base: 800256, range: 2, status-vector: 0x0, offset: 1
                Localpref: 100
                Router ID: 192.168.2.1
                Primary Routing Table bgp.l2vpn.0

 65512:200:2:1/96 (1 entry, 1 announced)
        *L2VPN  Preference: 170/-101
                Next hop type: Indirect, Next hop index: 0
                Address: 0xce2f190
                Next-hop reference count: 3
                Protocol next hop: 192.168.2.4
                Indirect next hop: 0x0 - INH Session ID: 0x0
                State: <Active Int Ext>
                Age: 1d 23:46:41        Metric2: 1
                Validation State: unverified
                Task: vpn-b-l2vpn
                Announcement bits (1): 1-BGP_RT_Background
                AS path: I
                Communities: Layer2-info: encaps: VLAN, control flags:[0x2] Control-Word, mtu: 0, site preference: 100
                Label-base: 800000, range: 2, status-vector: 0x0, offset: 1
                Secondary Tables: vpn-b.l2id.0

root@PE4>

PE4如何知道从CE连接到ge-0/0/0.515接口的帧必须与65512:200:1:1/96 NLRI相关联，从而得到内部标签为800257(2 + 800256 - 1)？

Answer 1

有两个标签，因此当流量从CE中吸收PE时，就会出现双重推送。

内标

每个接口都从那个L2VPNs标签块中获取一个标签。内部标签基于远程L2VPN站点的此接口特定标签。

L2VPN与VPLS使用相同的NLRI，因为它们包含：

• 航路识别器
• 边缘ID (站点ID)
• 标号块偏移量
• 标签块大小
• 标签库

如果不是多宿主，则每个L2VPN CE接口都有自己的站点ID，因此在设备上分配自己的标签。如果您是多归属，两者都是相同的网站，将使用相同的标签，但需要额外的路由选择，以确定哪个电路是活动的。

BGP NLRI中的信息允许本地和远程PE为发送和接收导出内部标签值。每一个CE都是自己的站点，双方都可以计算出每一个必需的CE到CE标签所需。记住，标签块本质上是本地重要的，也就是说，每个PE的标签块不一定是相同的。

您可以查看L2VPN连接以查看标签详细信息。

jhead@L2VPN-PE1> show l2vpn connections instance L2VPN-NESE
Layer-2 VPN connections:

<...snip...>

Instance: L2VPN-NESE
Edge protection: Not-Primary
  Local site: 1 (1)
    connection-site           Type  St     Time last up          # Up trans
    2                         rmt   Up     Jan  7 19:45:02 2021           1
      Remote PE: 2.2.2.2, Negotiated control-word: No
      Incoming label: 800183, Outgoing label: 800000
      Local interface: xe-0/0/7.119, Status: Up, Encapsulation: VLAN
      Flow Label Transmit: No, Flow Label Receive: No

此外，您可以看到mpls.0表的本地接口的标签关联。

jhead@L2VPN-PE1> show route label 800183

mpls.0: 1063 destinations, 1063 routes (1063 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

800183             *[L2VPN/7] 3w6d 22:34:47
                    > via xe-0/0/7.119, Pop

外标

外部标签是与LSP关联到远程PE (RSVP / LDP)的传输标签。