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答：

配置思路：

underlay配置ospf互通，并配置CE3为RR，CE1,CE2为客户端，建立BGP EVPN邻居。

CE1,CE2创建创建实例A，分配vxlan vni，然后分别在CE1和CE2上绑定实例A，创建

BD，并绑定实例A。对应接口下创建二层子接口绑定BD和VLAN id。

CE1,CE2建立Vbdif接口分配网关地址，实现分布式网关。

    CE3上建立三层实例X，为实例配置去往外网的默认路由，并在bgp 实例下引入静态路

由和下发静态路由

关键配置：

CE1：

evpn-overlay enable

#

ip vpn-instance A

 ipv4-family

  route-distinguisher 100:1

  vpn-target 11:1 export-extcommunity evpn

  vpn-target 11:1 import-extcommunity evpn

 vxlan vni 100

#

bridge-domain 15

 vxlan vni 15

 evpn

  route-distinguisher 100:1

  vpn-target 100:100 export-extcommunity

  vpn-target 11:1 export-extcommunity

  vpn-target 100:100 import-extcommunity

#

bridge-domain 20

 vxlan vni 20

 evpn

  route-distinguisher 100:2

  vpn-target 200:200 export-extcommunity

  vpn-target 11:1 export-extcommunity

  vpn-target 200:200 import-extcommunity

#

interface Vbdif15

 ip binding vpn-instance A

 ip address 192.168.15.254 255.255.255.0

 mac-address 0000-005e-0115

 vxlan anycast-gateway enable

 arp collect host enable

#

interface Vbdif20

 ip binding vpn-instance A

 ip address 192.168.20.254 255.255.255.0

 mac-address 0000-005e-0120

 vxlan anycast-gateway enable

 arp collect host enable

#

interface GE1/0/1.15 mode l2

 encapsulation dot1q vid 15

 bridge-domain 15

#

interface GE1/0/1.20 mode l2

 encapsulation dot1q vid 20

 bridge-domain 20

#

#

interface Nve1

 source 1.1.1.1

 vni 15 head-end peer-list protocol bgp

 vni 20 head-end peer-list protocol bgp

#

bgp 100

 peer 3.3.3.3 as-number 100

 peer 3.3.3.3 connect-interface LoopBack0

 #

 ipv4-family unicast

  peer 3.3.3.3 enable

 #

 l2vpn-family evpn

  policy vpn-target

  peer 3.3.3.3 enable

  peer 3.3.3.3 advertise irb

#

ospf 1 router-id 1.1.1.1

 area 0.0.0.0

  network 1.1.1.1 0.0.0.0

  network 15.1.1.1 0.0.0.0

#

CE2配置类似

CE3:

#

evpn-overlay enable

#

ip vpn-instance X

 ipv4-family

  route-distinguisher 100:3

  vpn-target 11:1 export-extcommunity evpn

  vpn-target 11:1 import-extcommunity evpn

 vxlan vni 200

#

interface GE1/0/1

 undo portswitch

 undo shutdown

 ip binding vpn-instance X

 ip address 39.1.1.3 255.255.255.0

#

interface Nve1

 source 3.3.3.3

#

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

  peer 1.1.1.1 enable

  peer 2.2.2.2 enable

 #

 ipv4-family vpn-instance X

  default-route imported

  import-route direct

  import-route static

  advertise l2vpn evpn

 #

 l2vpn-family evpn

  undo policy vpn-target

  peer 1.1.1.1 enable

  peer 1.1.1.1 advertise irb

  peer 1.1.1.1 reflect-client

  peer 2.2.2.2 enable

  peer 2.2.2.2 advertise irb

  peer 2.2.2.2 reflect-client

#

ospf 1 router-id 3.3.3.3

 area 0.0.0.0

  network 3.3.3.3 0.0.0.0

  network 35.1.1.3 0.0.0.0

#

ip route-static vpn-instance X 0.0.0.0 0.0.0.0 39.1.1.9

最终实验效果截图：