某局点S6805交换机对接虚拟机部分BFD会话无法UP的经验案例

S6805与很多虚拟机直连并建立BGP邻居，同时配置BFD检测。

部分BGP邻居的BFD会话无法UP

===============display bfd session verbose=============== 

 Total Session Num: 20     Up Session Num: 5     Init Mode: Active

 IPv4 session working in control packet mode:

       Local Discr: 1025                 Remote Discr: 0

         Source IP: 10.66.137.137      Destination IP: 10.66.137.138

     Session State: Down                    Interface: Vlan-interface999

      Min Tx Inter: 400ms                Act Tx Inter: 100ms

      Min Rx Inter: 400ms                Detect Inter: 5000ms

          Rx Count: 0                        Tx Count: 12845730

      Connect Type: Direct             Running Up for: 00:00:00

         Hold Time: 0ms                     Auth mode: None

       Detect Mode: Async                        Slot: 1

          Protocol: MAD            

           Version: 1              

         Diag Info: No Diagnostic

    Local Discr: 1069                 Remote Discr: 1363766235

         Source IP: 10.66.140.1        Destination IP: 10.66.140.2

     Session State: Up                      Interface: N/A

      Min Tx Inter: 400ms                Act Tx Inter: 400ms

      Min Rx Inter: 400ms                Detect Inter: 2000ms

          Rx Count: 310                      Tx Count: 291

      Connect Type: Indirect           Running Up for: 00:01:41

         Hold Time: 1823ms                  Auth mode: None

       Detect Mode: Async                        Slot: 2

          Protocol: BGP            

           Version: 1              

         Diag Info: No Diagnostic   

1、通过在设备侧采集BFD的debug信息，发现有很多BFD控制报文被丢弃，原因是无效的端口号

*Apr 28 18:27:23:618 2021 ***.***.cn6 BFD/7/DEBUG: -Slot=2; [K]Recv from OAM:Ctrl packet, Src:10.66.137.137, Dst:10.66.137.138, Ver:1, Diag:0, Sta:1 P/F/C/A/D/M:0/0/1/0/0/0, Mult:5 LD/RD:1025/0, Tx:100ms, Rx:100ms, EchoRx:0ms

*Apr 28 18:27:24:634 2021 ***.***.cn6 BFD/7/DEBUG: [K]Invalid UDP source port. Discard packet.

2、通过抓包发现无法UP的BFD会话，虚拟机发出的控制报文源端口大多是3w多

3、标准协议规定BFD的src port不能小于49152，我司设备也是按照标准协议实现的

虚拟机侧修改配置，保证发出的BFD报文源端口大于49152