我在 ASR1k 和 ASR9k 之间的 BGP 上设置 BFD。在 1k #show bfd 邻居详细信息不会产生任何输出。好像 BFD 没有运行。CPU 进程在 1k 上运行：BFD HW EVENT、BFD IPV6 ADDR、BFD 会话创建 BFD HA。

我们在子接口和 vrf 上使用双重标记。我错过了什么？根据 cisco 配置，应该很容易打开 bfd。

Please see below configuration:
router bgp 66000
 bgp router-id 10.10.10.1
 bgp log-neighbor-changes
 timers bgp 10 30
 !
 address-family ipv4 vrf 1001
  redistribute connected
  redistribute static
  neighbor x.x.x.0 remote-as 65000
  neighbor x.x.x.0 ttl-security hops 2
  neighbor x.x.x.0 fall-over bfd multi-hop
  neighbor x.x.x.0 activate
  neighbor x.x.x.0 soft-reconfiguration inbound
  neighbor y.y.y.0 remote-as 65000
  neighbor y.y.y.0 ttl-security hops 2
  neighbor y.y.y.0 fall-over bfd single-hop
  neighbor y.y.y.0 activate
  neighbor y.y.y.0 soft-reconfiguration inbound
  maximum-paths 2
  default-information originate
 exit-address-family
 !

ASR1K1#sh run int gi0/0/0.3999
interface GigabitEthernet0/0/0.3999
 description Ethernet Primary WAN
 encapsulation dot1Q 3999 second-dot1q 1
 vrf forwarding 1001
 ip address x.x.x.1 255.255.255.254
 bfd interval 500 min_rx 100 multiplier 3
end

ASR1K1#sh run int Gi0/0/1.3999
Building configuration...

Current configuration : 267 bytes
!
interface GigabitEthernet0/0/1.3999
 description Ethernet Secondary WAN
 encapsulation dot1Q 3999 second-dot1q 1
 vrf forwarding 1001
 ip address y.y.y.1 255.255.255.254
 bfd interval 500 min_rx 100 multiplier 3
end

命令 show bfd neighbors 不显示任何内容。

ASR1K1#sh bfd neighbors vrf 1001 details 
ASR1K1#

ASR9k 显示 bfd 会话目标 xxx 详细信息：

-------------------------------------ASR9k-1----------------------------------
RP/0/RSP0/CPU0:ASR9k1#sh bfd session destination x.x.x.1 detail 
Sun Sep 25 17:34:50.176 BST

Location: 0/2/CPU0
Dest: x.x.x.1
Src: x.x.x.0
VRF Name/ID: 1001/0x60000008
 State: DOWN for 0d:5h:32m:3s, number of times UP: 0
 Session type: SW/V4/MH
Received parameters:
 Version: 0, desired tx interval: 0 us, required rx interval: 0 us
 Multiplier: 0, diag: None
 My discr: 0, your discr: 0, H/D/F/P/C/A: 0/0/0/0/0/0
Transmitted parameters:
 Version: 1, desired tx interval: 2 s, required rx interval: 2 s
 Multiplier: 3, diag: None
 My discr: 25523, your discr: 0, state DOWN, D/F/P/C/A: 0/0/0/1/0
Timer Values:
 Local negotiated async tx interval: 2 s
 Remote negotiated async tx interval: 2 s
async detection time: 0 us
Local Stats:
 Intervals between async packets:
   Tx: Number of intervals=100, min=1665 ms, max=1998 ms, avg=1853 ms
       Last packet transmitted 338 ms ago
   Rx: Number of intervals=0, min=0 s, max=0 s, avg=0 s
       Last packet received 0 s ago
MP download state: BFD_MP_DOWNLOAD_ACK
State change time: Sep 25 12:02:46.886
Session owner information:
                            Desired               Adjusted
  Client               Interval   Multiplier Interval   Multiplier
  -------------------- --------------------- ---------------------
  bgp-default          500 ms     3          2 s        3         
  bgp-default          500 ms     3          2 s        3      

-------------------------------------ASR9k-2----------------------------------      

RP/0/RSP0/CPU0:ASR9k2#sh bfd session destination y.y.y.1 detail 
Sun Sep 25 17:34:05.477 BST
I/f: GigabitEthernet0/3/0/0.3999, Location: 0/3/CPU0
Dest: y.y.y.1
Src: y.y.y.0
 State: DOWN for 2d:1h:34m:36s, number of times UP: 0
 Session type: PR/V4/SH
Received parameters:
 Version: 0, desired tx interval: 0 us, required rx interval: 0 us
 Required echo rx interval: 0 us, multiplier: 0, diag: None
 My discr: 0, your discr: 0, H/D/F/P/C/A: 0/0/0/0/0/0
Transmitted parameters:
 Version: 1, desired tx interval: 2 s, required rx interval: 2 s
 Required echo rx interval: 1 ms, multiplier: 3, diag: None
 My discr: 456472645, your discr: 0, state DOWN, D/F/P/C/A: 0/0/0/1/0
Timer Values:
 Local negotiated async tx interval: 2 s
 Remote negotiated async tx interval: 2 s
 Desired echo tx interval: 500 ms, local negotiated echo tx interval: 0 us
 Echo detection time: 0 us, async detection time: 0 us
Local Stats:
 Intervals between async packets:
   Tx: Number of intervals=100, min=1664 ms, max=2 s, avg=1846 ms
       Last packet transmitted 1811 ms ago
   Rx: Number of intervals=0, min=0 s, max=0 s, avg=0 s
       Last packet received 0 s ago
 Intervals between echo packets:
   Tx: Number of intervals=0, min=0 s, max=0 s, avg=0 s
       Last packet transmitted 0 s ago
   Rx: Number of intervals=0, min=0 s, max=0 s, avg=0 s
       Last packet received 0 s ago
 Latency of echo packets (time between tx and rx):
   Number of packets: 0, min=0 us, max=0 us, avg=0 us
Session owner information:
                            Desired               Adjusted
  Client               Interval   Multiplier Interval   Multiplier
  -------------------- --------------------- ---------------------
  bgp-default          500 ms     3          2 s        3         
  bgp-default          500 ms     3          2 s        3