拓扑说明：Underlay层使用isis协议，宣告每个设备的loopback接口
Spine1作为集中式网关，Leaf_1作为租户1的Leaf，vlan=10 vxlan=10010，Leaf_2作为租户2的Leaf，vlan=20 vxlan=10020
需求：使用vxlan&evpn方式组网，使用集中式网关场景，最终PC1可以与PC2通讯，只展示Spine和Leaf的配置，Leaf2与Leaf1类似。

配置流程：

1. 开启evpn-overlay enable使能evpn为vxlan的控制层面
2. 创建相关BD，设置对应VXLAN，设置evpn的RD与RT
3. 建立BGP EVPN邻居关系
4. 配置NVE接口，指定源接口地址和头端复制，使用BGP协议
5. 在spine上配置vbdif接口
6. leaf上需要配置l2类型的子接口，关联相应的vlan和BD

Spine1：

#
sysname Spine-1
#
evpn-overlay enable
#
evpn
#
bridge-domain 10010
 vxlan vni 10010
 evpn
  route-distinguisher 10:10
  vpn-target 10:10 export-extcommunity
  vpn-target 10:10 import-extcommunity
#
bridge-domain 10020
 vxlan vni 10020
 evpn
  route-distinguisher 20:20
  vpn-target 20:20 export-extcommunity
  vpn-target 20:20 import-extcommunity
#
isis 1
 is-level level-2
 network-entity 86.0001.0010.0100.1001.00
#
interface Vbdif10010
 ip address 192.168.10.254 255.255.255.0
#
interface Vbdif10020
 ip address 192.168.20.254 255.255.255.0
#
interface GE1/0/0
 undo portswitch
 undo shutdown
 ip address 10.0.11.1 255.255.255.252
 isis enable 1
 isis circuit-type p2p
 isis circuit-level level-2
#
interface GE1/0/1
 undo portswitch
 undo shutdown
 ip address 10.0.12.1 255.255.255.252
 isis enable 1
 isis circuit-type p2p
 isis circuit-level level-2
#
interface LoopBack0
 ip address 1.1.1.1 255.255.255.255
 isis enable 1
#
interface Nve1
 source 1.1.1.1
 vni 10010 head-end peer-list protocol bgp
 vni 10020 head-end peer-list protocol bgp
#
bgp 100
 peer 3.3.3.3 as-number 100
 peer 3.3.3.3 connect-interface LoopBack0
 peer 4.4.4.4 as-number 100
 peer 4.4.4.4 connect-interface LoopBack0
 #
 ipv4-family unicast
  undo peer 3.3.3.3 enable
  undo peer 4.4.4.4 enable
 #
 l2vpn-family evpn
  policy vpn-target
  peer 3.3.3.3 enable
  peer 4.4.4.4 enable
#
return

Leaf_1：

#
sysname Leaf-1
#
evpn-overlay enable
#
bridge-domain 10010
 vxlan vni 10010
 evpn
  route-distinguisher 10:11
  vpn-target 10:10 export-extcommunity
  vpn-target 10:10 import-extcommunity
#
isis 1
 is-level level-2
 network-entity 86.0001.0030.0300.3003.00
#
interface GE1/0/0
 undo shutdown
#
interface GE1/0/0.10 mode l2
 encapsulation dot1q vid 10
 bridge-domain 10010
#
interface GE1/0/1
 undo portswitch
 undo shutdown
 ip address 10.0.11.2 255.255.255.252
 isis enable 1
 isis circuit-type p2p
 isis circuit-level level-2
#
interface GE1/0/2
 undo portswitch
 undo shutdown
 ip address 10.0.21.2 255.255.255.252
 isis enable 1
 isis circuit-type p2p
 isis circuit-level level-2
#
interface LoopBack0
 ip address 3.3.3.3 255.255.255.255
 isis enable 1
#
interface Nve1
 source 3.3.3.3
 vni 10010 head-end peer-list protocol bgp
#
interface NULL0
#
bgp 100
 peer 1.1.1.1 as-number 100
 peer 1.1.1.1 connect-interface LoopBack0
 peer 2.2.2.2 as-number 100
 peer 2.2.2.2 connect-interface LoopBack0
 #
 ipv4-family unicast
  undo peer 1.1.1.1 enable
  undo peer 2.2.2.2 enable
 #
 l2vpn-family evpn
  policy vpn-target
  peer 1.1.1.1 enable
  peer 2.2.2.2 enable
#
return

实验现象：