在Nexus 9000交換機上配置和驗證BFD

簡介

本文檔介紹如何在基於Cisco Nexus NXOS®的交換機上配置和驗證雙向轉發檢測(BFD)會話。

必要條件

需求

思科建議您瞭解以下主題：

• 雙向轉送偵測(BFD)
• Nexus NX-OS軟體。
• 路由協定：開放最短路徑優先(OSPF)、邊界網關協定(BGP)、增強型內部網關路由協定(EIGRP)。
  
  

採用元件

本文檔中的資訊基於Cisco Nexus 9000(NXOS版本10.3(4a)。M)。

本文中的資訊是根據特定實驗室環境內的裝置所建立。文中使用到的所有裝置皆從已清除（預設）的組態來啟動。如果您的網路運作中，請確保您瞭解任何指令可能造成的影響。

設定

網路圖表

設定

配置BFD的目的是檢測並瞭解各種路由協定配置之間的差異。

第1步：在介面和協定上配置BFD之前，必須啟用BFD功能。

SW1(config)# feature bfd

SW2(config)# feature bfd

第2步：配置全局BFD

SW1(config)# bfd interval 500 min_rx 500 multiplier 3

SW2(config)# bfd interval 500 min_rx 500 multiplier 3

注意： min_tx和msec範圍從50到999毫秒，預設值為50。倍數範圍是從1到50。預設乘數為3。

第3步：在介面上配置BFD

注意：可以為介面上的所有BFD會話配置BFD會話引數。

警告：確保在啟用BFD的介面上停用網際網路控制消息協定(ICMP)重定向消息。在介面上使用no ip redirects或no ipv6 redirects命令。

SW1(config)# interface vlan 20 
SW1(config-if)# bfd interval 500 min_rx 500 multiplier 3
SW1(config-if)# no ip redirects
SW1(config-if)# no ipv6 redirects

SW2(config)# interface vlan 20 
SW2(config-if)# bfd interval 500 min_rx 500 multiplier 3
SW2(config-if)# no ip redirects
SW2(config-if)# no ipv6 redirects

BFD非同步模式類似於兩台裝置之間的握手，以保持其連線的強度。您可以在兩台裝置上設定它，當它打開時，它們會在設定的時間開始互相傳送特殊消息。這些訊息有一些重要的設定，例如傳送頻率，以及一台裝置回應另一台裝置的速度。還有一個設定會決定一台裝置需要多少則遺漏訊息，才能意識到連線可能發生問題。

BFD回送功能會將測試封包傳送給鄰居，然後讓它們傳回以檢查問題，而不需要讓鄰居參與封包轉送。它可以使用較慢的計時器來減少控制資料包流量，並在鄰居系統上測試轉發路徑，而不會影響鄰居，從而加快檢測速度。如果兩個鄰居都使用回聲功能，則不存在不對稱。

系統日誌BFD關閉原因 

• Path Down：這表示兩個BFD鄰居之間的轉發路徑不再運行，這可能是由於網路擁塞、硬體故障或其他問題。
  

  2024 Apr 11 22:07:07 SW2 %BFD-5-SESSION_STATE_DOWN: BFD session 1090519062 to neighbor 172.16.1.1 on interface Vlan20 has gone down. Reason: Path Down.

• Echo函式失敗：Echo函式失敗，這是BFD的一個功能，用於傳送和接收回應資料包以驗證連線。如果這些資料包未能成功傳輸或接收，則表明存在問題。
  

  2024 Apr 11 22:17:45 SW2 %BFD-5-SESSION_STATE_DOWN: BFD session 1090519174 to neighbor 10.10.10.1 on interface Vlan10 has gone down. Reason: Echo Function Failed.

• 鄰居發訊號會話關閉：鄰居裝置發出BFD會話關閉的訊號，通常是因為檢測到連線結束時出現問題。
  

  2024 Apr 11 22:03:48 SW2 %BFD-5-SESSION_STATE_DOWN: BFD session 1090519058 to neighbor 172.16.1.1 on interface Vlan20 has gone down. Reason: Neighbor Signaled Session Down.

• Control Detection Time Expired：當控制檢測計時器在收到來自鄰居的預期響應（表示連線存在潛在問題）之前超時時會發生這種情況。
  

  2024 Apr 11 22:19:31 SW2 %BFD-5-SESSION_STATE_DOWN: BFD session 1090519061 to neighbor 192.168.2.1 on interface Lo30 has gone down. Reason: Control Detection Time Expired.

• 管理性關閉：BFD會話由管理員故意關閉，可能出於維護目的或由於配置更改而關閉。
  

  2024 Apr 11 22:13:15 SW2 %BFD-5-SESSION_STATE_DOWN: BFD session 1090519064 to neighbor 10.10.10.1 on interface Vlan10 has gone down. Reason: Administratively Down.

  
  


在路由協定上配置BFD




在OSPF上配置BFD

提示：當在OSPF下啟用BFD時，它對於使用OSPF的所有介面都變為活動狀態。介面採用全局配置值。如果需要對這些值進行調整，請參閱步驟3「介面上的BFD配置」。

SW1(config)# router ospf 1
SW1(config-router)# bfd

SW2(config)# router ospf 1
SW2(config-router)# bfd

它還可以使用命令在OSPF介面下啟用BFDip ospf bfd



SW1(config)# interface vlan 10 
SW1(config-if)# ip ospf bfd

SW2(config)# interface vlan 10 
SW2(config-if)# ip ospf bfd

OSPF上的BFD配置示例

SW1# show running-config ospf !Command: show running-config ospf !Running configuration last done at: Wed Apr 10 21:06:31 2024 !Time: Wed Apr 10 21:09:45 2024 version 10.3(4a) Bios:version 01.07 feature ospf router ospf 1 bfd interface Vlan10 ip router ospf 1 area 0.0.0.0 ip ospf bfd

在EIGRP上配置BFD

SW1(config)# interface vlan 20 SW1(config-if)# ip eigrp 2 bfd

提示：當在EIGRP下啟用BFD時，它對於使用EIGRP的所有介面都變為活動狀態。介面採用全局配置值。如果需要對這些值進行調整，請參閱步驟3「介面上的BFD配置」。

SW1(config)# router eigrp 2
SW1(config-router)# bfd

SW2(config)# router eigrp 2
SW2(config-router)# bfd

它還可以使用命令在EIGRP介面下啟用BFDip eigrp instance-tag bfd

SW1(config)# interface vlan 20 
SW1(config-if)# ip eigrp 2 bfd

SW2(config)# interface vlan 20 
SW2(config-if)# ip eigrp 2 bfd

EIGRP上的BFD配置示例

SW1# show running-config eigrp !Command: show running-config eigrp !Running configuration last done at: Wed Apr 10 21:24:29 2024 !Time: Wed Apr 10 21:53:08 2024 version 10.3(4a) Bios:version 01.07 feature eigrp router eigrp 2 address-family ipv4 unicast bfd interface Vlan20 ip router eigrp 2 ip eigrp 2 bfd

在BGP上配置BFD

注意：在與鄰居建立BGP會話期間，更新源功能有助於BGP會話利用指定介面的主IP地址作為本地地址。此外，它使BGP能夠註冊為BFD的客戶端。

注意：在裝置上配置BFD會話時，指定「multihop」或「singlehop」將確定會話型別。如果未提供關鍵字，則當對等體直接連線時，會話型別預設為「singlehop」。如果對等體未連線，則會話型別預設為「multihop」。

SW1(config)#  router bgp 65001
SW1(config-router)# address-family ipv4 unicast
SW1(config-router)# neighbor  192.168.3.1
SW1(config-router-neighbor)# bfd multihop
SW1(config-router-neighbor)# update-source loopback30

SW2(config)# router bgp 65002
SW2(config-router)# address-family ipv4 unicast
SW2(config-router)#  neighbor 192.168.2.1
SW2(config-router-neighbor)#  bfd multihop
SW2(config-router-neighbor)# update-source loopback30

BGP上的BFD配置示例

SW1# show running-config bgp !Command: show running-config bgp !Running configuration last done at: Thu Apr 11 04:47:53 2024 !Time: Thu Apr 11 06:48:43 2024 version 10.3(4a) Bios:version 01.07 feature bgp router bgp 65001 address-family ipv4 unicast neighbor 192.168.3.1 bfd multihop remote-as 65002 update-source loopback30 ebgp-multihop 5 address-family ipv4 unicast 


驗證

配置BFD並將其與協定（如OSPF、EIGRP或BGP）關聯後，必須自動辨識BFD鄰居。要確認這一點，請使用以下命令：

show bfd neighbors

在交換機1上

 SW1# show bfd neighbors OurAddr NeighAddr LD/RD RH/RS Holdown(mult) State Int Vrf Type BSID 172.16.1.1 172.16.1.2 1090519059/1090519058 Up 5219(3) Up Vlan20 default SH N/A 10.10.10.1 10.10.10.2 1090519060/1090519059 Up 5219(3) Up Vlan10 default SH N/A 192.168.2.1 192.168.3.1 1090519062/1090519061 Up 728(3) Up Lo30 default MH N/A SW1# 

在交換機2上

SW2# show bfd neighbors OurAddr NeighAddr LD/RD RH/RS Holdown(mult) State Int Vrf Type BSID 172.16.1.2 172.16.1.1 1090519058/1090519059 Up 5053(3) Up Vlan20 default SH N/A 10.10.10.2 10.10.10.1 1090519059/1090519060 Up 5053(3) Up Vlan10 default SH N/A 192.168.3.1 192.168.2.1 1090519061/1090519062 Up 745(3) Up Lo30 default MH N/A 

要確認此情況並獲取詳細輸出，請使用命令：

SW1# show bfd neighbors interface lo30 details OurAddr NeighAddr LD/RD RH/RS Holdown(mult) State Int Vrf Type BSID 192.168.2.1 192.168.3.1 1090519062/1090519061 Up 676(3) Up Lo30 default MH N/A Session state is Up and not using echo function Session type: Multihop Local Diag: 0, Demand mode: 0, Poll bit: 0, Authentication: None MinTxInt: 250000 us, MinRxInt: 250000 us, Multiplier: 3 Received MinRxInt: 250000 us, Received Multiplier: 3 Holdown (hits): 750 ms (0), Hello (hits): 250 ms (82590) Rx Count: 82588, Rx Interval (ms) min/max/avg: 207/1764/219 last: 73 ms ago Tx Count: 82590, Tx Interval (ms) min/max/avg: 219/219/219 last: 67 ms ago Registered protocols: bgp Uptime: 0 days 5 hrs 2 mins 2 secs, Upcount: 1 Last packet: Version: 1 - Diagnostic: 0 State bit: Up - Demand bit: 0 Poll bit: 0 - Final bit: 0 Multiplier: 3 - Length: 24 My Discr.: 1090519061 - Your Discr.: 1090519062 Min tx interval: 250000 - Min rx interval: 250000 Min Echo interval: 0 - Authentication bit: 0 Hosting LC: 1, Down reason: None, Reason not-hosted: None

SW2# show bfd neighbors interface vlan 20 details OurAddr NeighAddr LD/RD RH/RS Holdown(mult) State Int Vrf Type BSID 172.16.1.2 172.16.1.1 1090519058/1090519059 Up 4979(3) Up Vlan20 default SH N/A Session state is Up and using echo function with 500 ms interval Session type: Singlehop Local Diag: 0, Demand mode: 0, Poll bit: 0, Authentication: None MinTxInt: 500000 us, MinRxInt: 2000000 us, Multiplier: 3 Received MinRxInt: 2000000 us, Received Multiplier: 3 Holdown (hits): 6000 ms (0), Hello (hits): 2000 ms (12454) Rx Count: 12444, Rx Interval (ms) min/max/avg: 109/1919/1908 last: 1020 ms ago Tx Count: 12454, Tx Interval (ms) min/max/avg: 1906/1906/1906 last: 856 ms ago Registered protocols: eigrp Uptime: 0 days 6 hrs 35 mins 10 secs, Upcount: 2 Last packet: Version: 1 - Diagnostic: 0 State bit: Up - Demand bit: 0 Poll bit: 0 - Final bit: 0 Multiplier: 3 - Length: 24 My Discr.: 1090519059 - Your Discr.: 1090519058 Min tx interval: 500000 - Min rx interval: 2000000 Min Echo interval: 500000 - Authentication bit: 0 Hosting LC: 1, Down reason: None, Reason not-hosted: None

使用會話詳細資訊進行驗證

SW1# sh bfd clients Client : Number of sessions bgp : 1 ospf : 1 eigrp : 1 SW1# show system internal bfd sess-store interface vlan 10 No of sessions: 1 >>>>> Check Number of sessions 0x4100001b - 0x41000019 Hosting LC: 1 10.10.10.1 -> 10.10.10.2 bsid 0 >>>>> Check IP addresses BFD_SESS_ST_SESSION_UP for 0 days 0:6:22 594 >>>>> Check uptime Vlan10 [2 0x901000a:0x43 0:10 0x1000c 0x1000c] SMAC: 4464.3c81.ddd7 DMAC: 4464.3c81.cdb7 Local TX/RX/ST(ms): 500/500/2000000 Mult: 3 EchoRx: 50000 Ver:1 Flags(0x0): Echo Auth Interop (Disabled) Auth(0 0 0) Group id 0x0 Active TX/RX/ST(ms): 2000/2000/2000000 Mult: 3 State: 3 Diag: 0x0 Flags: 0xc 0000 Auth(0 0 0) Spray DIs: 0 Port-Lcs: Module 1 has 2 links - ACL not programmed Applications: (1) ospf [0x1:0x41000119 flags 0x0] App Data : [c0a80301000] Description: 10.10.10.2 MTS Dest 0xfe000001:0x140 No-Host reason: 0x0(SUCCESS) Counters: >>>>>>>> Check the counters below Retries: LC remove(0), ACL Inst/Rem(0/0), Redisc(0) No. of ACLs Added(1) Flap counters: Ctrl Detect timer expired(0), Echo failed(0), Neigh Signaled down(0), Admin d own(0), Forwarding plane reset(0), Path down(0), Concat path down(0), Rev Concat path down(0) Last ACL added time: 58781 usecs after Thu Apr 11 22:18:19 2024 Last ACL response time: 81830 usecs after Thu Apr 11 22:18:19 2024 Last session install time: 58285 usecs after Thu Apr 11 22:18:19 2024 Last session install response time: 58717 usecs after Thu Apr 11 22:18:19 2024 

使用訪問清單進行驗證

SW2# show system internal access-list vlan 10 input statistics slot 1 ======= INSTANCE 0x0 --------------- Tcam 12 resource usage: ---------------------- LBL M = 0x1 Bank 0 ------ IPv4 Class Policies: BFD() [Merged] Netflow profile: 0 Netflow deny profile: 0 Entries: [Index] Entry [Stats] --------------------- [0x0000:0x0003:0x0c0d] permit udp 0.0.0.0/0 0.0.0.0/0 range 3784 3785 encap 0x0 [205340] >>>>> This counter needs to increase SW2# show system internal access-list sup-redirect-stats | i i bfd 3085 BFD 12217 >>>>> This counter need to increase 3121 BFDC TCLASS PACKET 0 3146 BFDC v4 PACKET 15 3148 BFDC TCLASS V6 PACKET 0 3156 BFDC v6 PACKET 0 3158 BFDC v6 LL Ucast PACKET 0 3209 BFDC v4 multihop PACKET 383697 >>>>> This counter need to increase in multihop case 3121 BFDC TCLASS PACKET 0 3146 BFDC v4 PACKET 0 3148 BFDC TCLASS V6 PACKET 0 3156 BFDC v6 PACKET 0 3158 BFDC v6 LL Ucast PACKET 0 3209 BFDC v4 multihop PACKET 0

使用Ethanalyzer驗證 



另一種方法是執行資料包捕獲，特別是針對UDP埠3785進行過濾。

SW1# ethanalyzer local interface inband display-filter "udp.port==3785" limit-captured-frames 0 Capturing on 'ps-inb' 5 2024-04-11 05:26:37.294596186 10.10.10.1 → 10.10.10.1 BFD Echo 70 Originator specific content 6 2024-04-11 05:26:37.294623155 10.10.10.1 → 10.10.10.1 BFD Echo 70 Originator specific content 7 2024-04-11 05:26:37.294635837 172.16.1.1 → 172.16.1.1 BFD Echo 70 Originator specific content 8 2024-04-11 05:26:37.294653159 172.16.1.1 → 172.16.1.1 BFD Echo 70 Originator specific content 4 18 2024-04-11 05:26:37.780441619 10.10.10.1 → 10.10.10.1 BFD Echo 70 Originator specific content 19 2024-04-11 05:26:37.780461351 172.16.1.1 → 172.16.1.1 BFD Echo 70 Originator specific content 20 2024-04-11 05:26:37.780467533 10.10.10.1 → 10.10.10.1 BFD Echo 70 Originator specific content 21 2024-04-11 05:26:37.780481315 172.16.1.1 → 172.16.1.1 BFD Echo 70 Originator specific content 30 2024-04-11 05:26:38.266365493 10.10.10.1 → 10.10.10.1 BFD Echo 70 Originator specific content 31 2024-04-11 05:26:38.266392766 10.10.10.1 → 10.10.10.1 BFD Echo 70 Originator specific content

在從BFD回聲協定捕獲的資料包中，預期存在相同的源IP地址和目的IP地址，因為這些回聲資料包源自本地交換機本身。



注意：如果介面下沒有「no bfd echo」語句，捕獲將同時顯示具有本地源IP地址和相鄰目標IP地址的資料包，並觀察BFD控制

SW2# ethanalyzer local interface inband display-filter "ip.addr==192.168.2.1" limit-captured-frames 0 Capturing on 'ps-inb' 1 2024-04-11 05:38:21.155483591 192.168.2.1 → 192.168.3.1 BFD Control 66 Diag: No Diagnostic, State: Up, Flags: 0x00 2 2024-04-11 05:38:21.182606602 192.168.3.1 → 192.168.2.1 BFD Control 66 Diag: No Diagnostic, State: Up, Flags: 0x00 11 2024-04-11 05:38:21.375187034 192.168.2.1 → 192.168.3.1 BFD Control 66 Diag: No Diagnostic, State: Up, Flags: 0x00 12 2024-04-11 05:38:21.402295701 192.168.3.1 → 192.168.2.1 BFD Control 66 Diag: No Diagnostic, State: Up, Flags: 0x00 4 14 2024-04-11 05:38:21.594612491 192.168.2.1 → 192.168.3.1 BFD Control 66 Diag: No Diagnostic, State: Up, Flags: 0x00 15 2024-04-11 05:38:21.621742431 192.168.3.1 → 192.168.2.1 BFD Control 66 Diag: No Diagnostic, State: Up, Flags: 0x00 20 2024-04-11 05:38:21.813971234 192.168.2.1 → 192.168.3.1 BFD Control 66 Diag: No Diagnostic, State: Up, Flags: 0x00 8 21 2024-04-11 05:38:21.841086554 192.168.3.1 → 192.168.2.1 BFD Control 66 Diag: No Diagnostic, State: Up, Flags: 0x00 22 2024-04-11 05:38:22.033395440 192.168.2.1 → 192.168.3.1 BFD Control 66 Diag: No Diagnostic, State: Up, Flags: 0x00 23 2024-04-11 05:38:22.060526055 192.168.3.1 → 192.168.2.1 BFD Control 66 Diag: No Diagnostic, State: Up, Flags: 0x00 28 2024-04-11 05:38:22.252709432 192.168.2.1 → 192.168.3.1 BFD Control 66 Diag: No Diagnostic, State: Up, Flags: 0x00 29 2024-04-11 05:38:22.279810427 192.168.3.1 → 192.168.2.1 BFD Control 66 Diag: No Diagnostic, State: Up, Flags: 0x00