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One-Arm BFD Sessions Fail to Be Established on an NE20E V800R008C10SPC500

Publication Date:  2019-04-19 Views:  108 Downloads:  0

Issue Description

Version information:

NE20E-S: V800R008C10SPC500

S12704: V2R10C00SPC600

Networking description:

The two egress routers on a campus network are NE20E-Ss, and the core router is S12704 stacking which is connected to the NE20E-Ss in dual uplink. The outbound interface traffic is load balanced to different carriers. NAT is enabled on the NE20E-Ss.

Configuration script:

The interfaces apply the EasyIP NAT mode.

nat instance unicom id 1
 service-instance-group 1
 nat address-group unicom group-id 0 unnumbered interface GigabitEthernet0/1/0
nat instance unicom id 2
 service-instance-group 1
 nat address-group 1 group-id 0
  section 0

BFD configuration:

bfd unicom bind peer-ip x.x.x.1 interface GigabitEthernet0/1/0 source-ip x.x.x.2 one-arm-echo
 discriminator local 1

Check information about the BFD session. It is found the BFD session fails to be set up.

[~NE20E-S8-1]dis bfd se all v
(w): State in WTR
(*): State is invalid
  (One Hop)   State : Down                  Name : unicom
  Local Discriminator    : 1                Remote Discriminator   : -
  Session Detect Mode    : Asynchronous One-arm-echo Mode
  BFD Bind Type          : Interface(GigabitEthernet0/1/0) 
  Bind Session Type      : Static 
  Bind Peer IP Address   : x.x.x.1     
  Bind Interface         : GigabitEthernet0/1/0                            
  Track Interface        : -
  Bind Source IP Address : x.x.x.2   
  FSM Board Id           : 9                TOS-EXP                : 7
  Echo Rx Interval (ms)  : 10
  Actual Tx Interval (ms): -                Actual Rx Interval (ms): -
  Local Detect Multi     : 3                Detect Interval (ms)   : -
  Echo Passive           : Disable          Acl Number             : -
  Destination Port       : 3784             TTL                    : 255
  Proc Interface Status  : Disable          Process PST            : Disable   
  WTR Interval (ms)      : -                Config PST             : Disable   
  Active Multi           : -                 
  Last Local Diagnostic  : Control Detection Time Expired
  Bind Application       : No Application Bind
  Session TX TmrID       : -                Session Detect TmrID   : -
  Session Init TmrID     : -                Session WTR TmrID      : -
  Session Echo Tx TmrID  : -  
  Session Not Up Reason  : In negotiation 
  Session Description    : -

Handling Process

Ping the peer device. The ping operation succeeds.

ping x.x.x.1
  PING x.x.x.2: 56  data bytes, press CTRL_C to break
    Reply from x.x.x.1: bytes=56 Sequence=1 ttl=254 time=3 ms
    Reply from x.x.x.1: bytes=56 Sequence=2 ttl=254 time=2 ms
    Reply from x.x.x.1: bytes=56 Sequence=3 ttl=254 time=8 ms
    Reply from x.x.x.1: bytes=56 Sequence=4 ttl=254 time=2 ms
    Reply from x.x.x.1: bytes=56 Sequence=5 ttl=254 time=2 ms

It is doubted that returned packets are filtered. After the NAT mode is changed to the address pool mode, the BFD session can be properly set up.

Root Cause

An interface configured with the EasyIP mode cannot function as the source end of a BFD session.